- What types of pregnancy tests are available?
- 4. You’ve had an extremely early miscarriage.
- 5. You have residual hCG in your system after a delivery or miscarriage.
- 6. You had an ectopic pregnancy.
- If you get a positive pregnancy test, the best thing to do is consult your doctor.
- Am I Really Pregnant? 9 Possible Reasons for a False-Positive Test
- Why You Might Get a False Negative or False Positive Pregnancy Test Result
- What is a False-Positive Pregnancy Test?
- Learn the reasons for a false-positive test result
- 4 Causes of a False Positive Pregnancy Test
- How to Avoid a False-Positive Pregnancy Test
- The truth about getting a false positive on your pregnancy test
- What can cause a false positive?
- What is a chemical pregnancy?
- What is an ectopic pregnancy?
- What is a molar pregnancy?
- Can I get a positive result after a recent pregnancy, miscarriage, or termination?
- What medical conditions could give me a false positive?
- Is It Possible to Get a False Positive Pregnancy Test Result?
- 1. Expired pregnancy test
- 2. Fertility medication
- 3. Miscarriage
- 4. Medication
- 5. Chemical pregnancy
- 6. Ectopic pregnancy
- 7. You’ve left the test sitting too long before looking
- 8. Medical conditions
- Houston Fertility Journal
- The most common causes The Most Common Causes of a False Positive Pregnancy Test
- An expired pregnancy test can yield a false positive
- Don’t let the test sit too long after completion before checking the results
- Having a miscarriage or “chemical pregnancy” can lead to a false positive
- Certain medications can distort pregnancy test results
- Having a molar or ectopic pregnancy
- Other medical conditions that can cause a false positive include:
- Your pregnancy test unit was faulty
- Your urine sample was contaminated
- Is There Such Thing As a False Negative Pregnancy Test?
- How can you know for sure whether or not you are actually pregnant?
- Want to learn more about pregnancy, infertility, and other things related to these subjects?
- How do pregnancy tests work?
- How accurate are pregnancy tests?
- How soon can I take a pregnancy test?
- Where can I get a pregnancy test?
- What should I do if my pregnancy test is positive?
- More questions from patients:
- False Negative Pregnancy Test: How to Identify the Hook Effect
- How does a home pregnancy test work?
- Why can I get a positive pregnancy test then negative?
- How can you tell if you’re experiencing the hook effect?
- Home pregnancy tests are very accurate if you use them correctly
- Home pregnancy tests can be 99% accurate
- Common causes of false results
- What to do next
- Related stories about pregnancy:
What types of pregnancy tests are available?
Two main types of pregnancy tests are blood tests and urine tests.
You get these at your doctor’s office, but they’re not used as often as urine tests. These tests can detect pregnancy earlier than a home pregnancy test, about 6 to 8 days after ovulation. It takes longer to get the results than with a home pregnancy test.
The two types of blood pregnancy tests are:
A qualitative hCG test simply checks for hCG. It gives a “yes” or “no” answer to the question, “Are you pregnant?” Doctors often order these tests to confirm pregnancy as early as 10 days after conception. Some can detect hCG much earlier.
A quantitative hCG test (beta hCG) measures the exact amount of hCG in your blood. It can find even very low levels of hCG. These tests may help track problems during pregnancy. Your doctor may use them along with other tests to rule out an ectopic pregnancy, when the fertilized egg implants outside your uterus, or after a miscarriage, when hCG levels fall quickly.
You can take these at home or in a doctor’s office.
Along with being private and convenient, home pregnancy tests are quick and easy to use. They’re also very accurate if you follow the directions. These pregnancy tests all work in a similar way. You test your pee in one of these ways:
- Hold the test stick in your urine stream
- Collect pee in a cup and dip the test stick into it
- Collect pee in a cup and use a dropper to put it into another container
You’ll need to wait a few minutes before seeing the results.
After you take this test, you can confirm your results by seeing your doctor, who can do even more sensitive pregnancy tests.
” women who are very motivated and trying to conceive, and they will often do the pregnancy test early and see a positive result, which is obviously very exciting for them initially,” Zev Williams, M.D., ob/gyn and assistant professor in the department of obstetrics and gynecology and women’s health at Albert Einstein College of Medicine, tells SELF. “But it just might be the result of the fertility medication that they took. It’s something we caution patients about so they don’t get false hope when they see that test is positive.”
4. You’ve had an extremely early miscarriage.
You might get your period a few days after a positive pregnancy test and assume you had a false-positive result. However, it could be that you were pregnant but miscarried very early on. “It’s not that the test is wrong—it was completely accurate at picking up the hormone ,” Dr. Williams says. “Unfortunately, this wasn’t a healthy pregnancy.” Doctors refer to this early pregnancy loss as a chemical pregnancy.
Most miscarriages occur in the first 13 weeks of pregnancy, and, although there are no real statistics, it’s estimated that many miscarriages occur before a woman even knows she’s pregnant. A chemical pregnancy occurs when a pregnancy is lost shortly after implantation, according to the American Pregnancy Association. Typically, it happens due to chromosomal abnormalities in the fertilized egg. Chemical pregnancies account for 50 to 75 percent of all miscarriages.
People who have a chemical pregnancy often experience bleeding (when they miscarry) right around the time of their expected period, which is why it’s easy to assume you just had a false-positive test result.
5. You have residual hCG in your system after a delivery or miscarriage.
After you give birth or miscarry, hCG can persist in your body for months, Dr. Williams says. The American Pregnancy Association estimates it takes four to six weeks for hCG levels to return to normal after a woman suffers a miscarriage. This is because some of the placenta can be left behind in the body, and it can continue to produce hCG for a short period of time. “As long as there are viable growing placenta cells inside the woman, those tests can be positive,” Dr. Williams says.
6. You had an ectopic pregnancy.
An ectopic pregnancy happens when a fertilized egg ends up growing outside the uterus—usually in a fallopian tube—instead of inside the uterus, according to the Mayo Clinic. That said, an ectopic pregnancy can also happen in other reproductive areas like the ovary or cervix. An ectopic pregnancy isn’t viable since the embryo isn’t inside the uterus where it can grow and thrive. But the embryo will still produce hCG, which can lead to a false-positive pregnancy test.
According to the Mayo Clinic, an ectopic pregnancy can be life-threatening. Call your doctor right away if you experience any of the following symptoms:
- Severe pain in your abdomen or pelvis while pregnant
- Vaginal bleeding (that’s out of the ordinary)
- Severe dizziness or lightheadedness
- Any other symptoms that are making you feel worried
If you get a positive pregnancy test, the best thing to do is consult your doctor.
Your ob/gyn can perform a blood test to further examine hCG levels and clear up any potential pregnancy test errors. Dr. Abdur-Rahman says he views at-home pregnancy tests more as “screening tests”—a blood test is a diagnostic test that can actually confirm you’re pregnant. If a blood test confirms you’re pregnant, your ob/gyn can continue to monitor hCG levels in your blood to make sure the pregnancy is developing properly before an ultrasound can reveal more details.
And if you get a negative pregnancy test, know that a false negative is possible, too. If you take an at-home pregnancy test too early, it might not pick up the hCG hormone. But, as we explained above, those hormones should double every 72 hours with a healthy pregnancy. “The longer you wait, the more likely you are to detect the pregnancy,” Dr. Williams says. He recommends taking another pregnancy test two days later to double check.
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Am I Really Pregnant? 9 Possible Reasons for a False-Positive Test
So what kinds of things can confuse your pregnancy test and cause it to erroneously give you some life-changing news?
Here’s a look at the most common causes:
You took the test too early
Pregnancy tests are most accurate when you follow the manufacturer’s directions exactly.
Though it can be tempting to take one the second you suspect you might be pregnant, it’s better to wait until a full week after your missed period. (Feels like an eternity, WE KNOW.) Tests are less accurate when taken before that, which means you could be more likely to get a false positive or false negative.
You had a chemical pregnancy
Chemical pregnancies happen when a fertilized egg is unable to implant or grow. The pregnancy is lost super early, and most women never even realize they happened.
But they can cause the body to start producing hCG, which could get picked up on a pregnancy test and cause a false-positive reading.
Chemical pregnancies are common and often occur for no reason. But they’re an important reason why it’s worth waiting at least a week after your missed period to take a pregnancy test: Holding off that long will reduce the chances that you get a false positive from any hCG that’s still in your system.
You have an ectopic pregnancy
Ectopic pregnancies are pregnancies that occur when a fertilized egg implants itself somewhere outside of the uterus — like one of the fallopian tubes, the cervix, the abdomen, or the ovaries.
These pregnancies aren’t viable because an egg can’t thrive and grow outside of the uterus. But early on, they can still cause the body to produce hCG and lead to a false-positive reading.
You might have an ectopic pregnancy if your test reads positive but you’re experiencing sharp waves of abdominal or pelvic pain, sharp pain on one side of your abdomen, spotting or bleeding, dizziness or fainting, or pressure in your rectum.
If you notice any of these symptoms, seek medical help ASAP. Ectopic pregnancies are health emergencies and they can damage your reproductive system if untreated.
You recently had a miscarriage
The body’s hCG levels start to drop back to pre-pregnancy levels after a miscarriage, but it doesn’t happen overnight. HCG can be detected in a woman’s blood for up to 6 weeks after a pregnancy loss.
So, if you were to try again to conceive shortly after a miscarriage, it’s possible for a test to pick up hCG from your previous pregnancy and give you a false-positive result.
You recently had an abortion
Abortions can cause subsequent false positives for the same reason that miscarriages can.
It can take up to 6 weeks for the hCG from your previous pregnancy to clear out of your system. So if you were to try again to conceive shortly after having an abortion, your test might read positive by mistake.
Your test showed an evaporation line
Some pregnancy tests use two lines to show a positive result (and just one line to show a negative one). The lines are usually bright blue or bright pink, but the second line can occasionally be faint.
Sometimes a faint second line can mean that you’re pregnant. But it can also just be an evaporation line — a meaningless line that forms after your urine has evaporated completely. Especially if the line is totally colorless.
Following the test’s directions to the letter can help you avoid evaporation lines. But if you really want to steer clear of this potential debacle, just pick a different pregnancy test.
Some digital tests use readouts like “Pregnant” or “Not Pregnant” instead of lines, which research shows are less likely to get misinterpreted.
You’re on fertility meds
If you’re undergoing fertility treatments, your doctor might prescribe a synthetic hCG trigger shot like Novarel, Pregnyl, Ovidrel, or Profasi. These shots prompt the follicles in your ovaries to release an egg, but they can also cause an OTC pregnancy test to give you a false positive.
This is especially likely to be the case if you take the test too early. Again, it’s another really good reason to hold off testing for a full week after your missed period.
You’re on other meds
Fertility meds aren’t the only drugs that could potentially mess with your test results. Other meds, too, can affect your hormone levels and potentially cause a pregnancy test to read positive by mistake.
Some common culprits include:
- anti-anxiety medications, like diazepam (Valium) or alprazolam (Xanax)
- antipsychotics, such as clozapine or chlorpromazine
- anticonvulsants, like phenobarbital or other barbiturates
- Parkinson’s disease medications, including bromocriptine (Parlodel)
- diuretics, like furosemide (Lasix, Diuscreen)
- methadone (Dolophine)
If you’re on one or more of these drugs and are trying to get pregnant, talk with your doctor. They can help you figure out the best steps to take to help you get an accurate test result, a safe pregnancy, and a healthy baby.
You have a medical condition
In addition to certain drugs, some medical conditions can also affect your hormone levels and potentially mess with your pregnancy test.
- urinary tract infections
- ovarian cysts
- kidney diseases
In rare cases, ovarian cancer or pituitary problems can also affect pregnancy test results.
Why You Might Get a False Negative or False Positive Pregnancy Test Result
Zave Smith/Getty Images
For roughly 10 percent of women in the U.S., getting pregnant is hard work—so you can only imagine the sadness and despair if they learn that their positive pregnancy test was actually a false alarm.
While rare, false positive pregnancy test and false negative pregnancy test results are entirely possible. Read on to find out what can cause them.
First, let’s talk about the science behind pregnancy tests: At-home pregnancy tests work by detecting human chorionic gonadotropin (HCG), a hormone created by placenta cells after an egg is fertilized, says Mary Jane Minkin, M.D., clinical professor of obstetrics, gynecology and reproductive sciences at Yale University School of Medicine. That hormone is excreted in your urine, which is how most tests determine whether or not you’re pregnant. For a pregnancy test to fail, it’s usually not because the test itself is faulty, but because of abnormal levels of HCG hormones in your urine, says Dr. Minkin.
Possible Causes of a False Positive Pregnancy Test
As mentioned, false pregnancy test results are rare, since the tests are generally considered 99-percent accurate—but certain factors can alter their results. (If you’re trying to get pregnant, also check out these Best Sex Positions to Get Pregnant.)
1. You had a miscarriage.
If you recently had a miscarriage, because you were pregnant, there may be leftover HCG in your system that could trigger a false positive result. When a pregnancy isn’t developing properly and results in a miscarriage, your body won’t release HCG as it normally would, says Dr. Minkin. But traces of the hormone could still be in your system afterward, which can lead to a positive pregnancy test. “It takes a while for the HCG to be cleared from the body,” says Dr. Minkin. In fact, HCG can linger for up to six weeks post-miscarriage, according to the American Pregnancy Association. (Related: How I Learned to Trust My Body Again After a Miscarriage)
2. It’s a side effect of medication.
Certain medications, like antidepressants and those that treat seizures, could interfere with your pregnancy test results. “Particular medications bind to the marker in the test as HCG would, making it look positive,” says Dr. Minkin. Again, this is unusual, but if you’re trying to get pregnant and are on medication, it’s important to talk to your doctor about its potential side effects and inferences.
3. You’re doing fertility treatments.
Ironically, fertility treatments can also mess with your test. “Some women receive an injection of the HCG hormone to help release the egg,” explains Dr. Minkin. In this case, the HCG triggering the positive result is likely coming from the injection, and not from an actual pregnancy. If you are on fertility treatments and get a positive result, your doctor should conduct a blood test to confirm whether or not you are indeed pregnant. (Learn more about What Ob-Gyns Wish Women Knew About Their Fertility.)
3. It’s a chemical pregnancy.
In a chemical pregnancy (the clinical term for a very early miscarriage), the sperm fertilizes the egg and your body starts making HCG, but soon the embryo stops developing and never turning into a fetus, explains Dr. Minkin. The evidence of fertilization, however—that small amount of HCG—could cause a false positive pregnancy test.
“Basically, the sperm and egg got together and started making some of the HCG, but then the embryo didn’t implant properly,” says Dr. Minkin. However, the HCG levels can be high enough that a pregnancy test can pick them up. (Related: Should You Eat Based On Your Menstrual Cycle?)
Possible Causes of a False Negative Pregnancy Test
1. You took the test too early.
False negative pregnancy test results do happen as well; however, in this case, it’s mostly due to human error, says Dr. Minkin. “Taking a test too early can result in a false negative because the embryo doesn’t start making detectable levels of HCG right away,” she says.
Typically, women ovulate on the fourteenth day of their menstrual cycles, but depending on the length of your cycle, you could ovulate a few days earlier or later. (Here are a few reasons your period could be irregular.) When you ovulate, your body releases an egg for fertilization to occur. It takes about eight to nine days after fertilization for the egg to develop into an embryo, implant onto the uterine wall, and be producing enough HCG to be detectable, says Dr. Minkin.
However, if you ovulated a little later in your cycle then you estimated, your HCG levels may still be low at the time of the test, says Dr. Minkin. A good rule of thumb is to take a test if you notice your period is late; if it’s negative, try again two or three days later or wait to see if your period shows up, she says. If it’s been a week and still no period, re-test or go to a doctor and ask for a blood test.
2. It’s an ectopic pregnancy.
An ectopic pregnancy is indeed a pregnancy, but the embryo develops in areas like the Fallopian tubes or cervix instead of the uterus. “With ectopic pregnancies, the HCG level is lower than in a pregnancy that is developing normally,” says Dr. Minkin, so you may actually be pregnant even though a test can turn up negative.
While they’re a rare occurrence, ectopic pregnancies could be dangerous. Common symptoms of an ectopic pregnancy can be abdominal pain and a missed period but, according to Dr. Minkin, the only way to be certain is through an ultrasound. If you think you could be having an ectopic pregnancy consult your doctor.
What to Do If You Think You Had a False Pregnancy Test Result
If you’re unsure whether or not you’re pregnant, you can always contact your healthcare provider and ask for a blood test—especially if you get a positive test result.
“A major advantage of blood tests is that they can measure how much of the HCG is present,” says Dr. Minkin. But rest assured: Pregnancy tests do live up to their 99-percent accuracy claims.
For the most accurate result, take the test right when you wake up, because that’s when your urine is most concentrated, suggests Dr. Minkin. If you’re unsure about the result, it’s a good idea to wait a couple of days and take another one (or go see your doctor).
Dr. Minkin also suggests taking a test such as First Response because they can detect around the same amount of HCG hormones as a blood test would. (Research published in 2011 supports First Response’s 99-percent accuracy claim for both the manual and digital test.) “But as long as you stick to the directions on the package, you should do OK,” says Dr. Minkin.
- By Bianca Mendez
What is a False-Positive Pregnancy Test?
Learn the reasons for a false-positive test result
Is the stick always right? Usually yes, but sometimes no. Learn about the rare reasons for a false-positive pregnancy test.
A home pregnancy test has confirmed what you suspected — you’re pregnant. Home pregnancy tests work by detecting the presence of the pregnancy hormone hCG in your urine. Their results are considered reliable, especially when you wait for at least a week after you miss your period to use one.
They’re not foolproof, however. It is possible to get a positive result when you’re not actually pregnant, which is called a false-positive. If you’ve been looking forward to a positive pregnancy test result, a false-positive is disappointing. The good news is they’re rare. The best thing to do when you’ve gotten a positive result is to contact your doctor. A blood test will confirm that you’re pregnant.
4 Causes of a False Positive Pregnancy Test
The four main causes that may lead to a false positive pregnancy test include a chemical pregnancy, a recent miscarriage, medication or a defective test. Read below to learn more about each of these scenarios.
A chemical pregnancy is a pregnancy, but an unhealthy one that results in an early miscarriage. A chemical pregnancy occurs when an egg has fertilized but doesn’t attach to the uterus. Usually, you will have a heavy period soon after your period is normally due. It’s estimated that 25-40 percent of pregnancies end as undetected miscarriages.
Recent miscarriage or birth
If you’ve had a baby recently or a miscarriage, you may test positive for pregnancy. When you’re pregnant, hCG levels rise quickly and peak at about 10 weeks. When a pregnancy ends, the levels go down, but slowly. The hormone can remain in your blood and urine for up to six weeks after a pregnancy ends.
If you’re undergoing fertility treatments to become pregnant, you may be getting hCG injections to stimulate ovulation. The medication can cause a false-positive result if you take the test too soon after a missed period.
Medications that may cause a false positive pregnancy:
- Antianxiety medications
- Parkinson’s disease medications
Defective pregnancy test or user error
Before buying a home pregnancy test, check to make sure it hasn’t expired. If it has, the chemical used to detect hCG may not work. It’s important to read and follow the test instructions carefully. For instance, some tests require leaving the dipstick in the urine stream for a specific amount of time. Taking the test too early can also result in a false-positive.
How to Avoid a False-Positive Pregnancy Test
The best way to avoid a false-positive pregnancy test is to wait at least a week after you’ve missed your period to take the test. The level of hCG hormone will be higher and easier to detect. Detecting a chemical pregnancy before it miscarries can be emotionally hard.
Many home pregnancy test kits include two tests. If you get a positive result, you can wait a couple of days and use the second test. Then contact your doctor for a blood test to confirm the good news!
Looking for an OB/GYN? We can help!
Topics: Family, Conditions & Care
Categories: Pregnancy, Women’s Health
Series: Birth of a Mom
When you get a positive pregnancy test result when you’re not expecting one, it can come as a huge shock. In this situation, it’s natural to wish that the results aren’t real. Many women who come to our center ask us if it’s possible they got a “false positive” on their home pregnancy test or the free test from our clinic. Learn more about how pregnancy tests work and the chances of getting a false positive, then contact Pregnancy Care Center of Grants Pass today by calling (541) 479-6264 to schedule a free appointment.
How Pregnancy Tests Work
Before talking about how a false positive can happen, it’s important to understand how a pregnancy test actually works.
When you become pregnant, your body starts going through a huge number of rapid changes to prepare for the pregnancy. Most of these changes are triggered by hormones that affect different parts of your body. Hormonal changes are also the reason many women experience symptoms during early pregnancy such as nausea, lightheadedness, cramping, and body aches.
A pregnancy test works by detecting these hormone levels in your urine – specifically, the hormone hCG, or human chorionic gonadotropin. This hormone is produced by your body when you are pregnant, from cells produced in the placenta. When a pregnancy test detects its presence in your urine, it almost always means you are pregnant.
However, it takes time for hCG levels to build up in your body. hCG levels roughly double in your bloodstream every three days, but they are too low to detect until about 12 days after conception. If you take a pregnancy test before this, you could still get a negative result, even if you are actually pregnant. These “false negatives” are very common in early pregnancy. Pregnancy Care Center of Grants Pass offers free, professional-grade pregnancy tests. Call us at (541) 479-6264 or visit our website to schedule an appointment if you are experiencing pregnancy symptoms but have received a negative pregnancy test result. For a list of possible pregnancy symptoms, visit our page on this topic here.
The Trouble with False Positives
While false negatives are very common, a false positive – where a pregnancy test tells you you’re pregnant when you aren’t – is extremely rare. That’s because there are very few circumstances when your body would produce hCG without being pregnant.
The most common cause of false positives is when you experience a “chemical pregnancy.” This term is slightly misleading, as a chemical pregnancy is actually a pregnancy, but it ends in very early miscarriage. Most chemical pregnancies spontaneously miscarry by about the fifth week. This is late enough that pregnancy tests can detect hCG in your body but too early for an ultrasound or other procedure. Contact your healthcare provider if you think you have experienced a miscarriage.
You can also get a positive pregnancy test result from an ectopic pregnancy, which is a pregnancy that implants outside the uterus. Ectopic pregnancies are relatively rare, but they are also extremely dangerous for the mother. If an ectopic pregnancy isn’t caught early, it could cause your fallopian tubes to rupture, causing massive internal injuries. A doctor or clinic can diagnose an ectopic pregnancy through an ultrasound examination. Contact your healthcare provider or go to the emergency room if you think you may have an ectopic pregnancy.
Medical Conditions and Medications
There are also some medical conditions that can cause false pregnancy positives. These conditions can vary, but some of the more common ones include urinary tract infections, ovarian cysts, and kidney diseases. Additionally, you can get a false pregnancy positive after taking certain medications, including anxiety medications like Xanax or Valium, medications containing promethazine, and certain antipsychotic and anticonvulsant medications.
Mistakes When Taking the Test
Finally, the most common cause of a false positive is simply not following instructions when taking a pregnancy test. You should always check to make sure the pregnancy test you are using isn’t expired, and you should carefully time how long the test is in your urine stream to get an accurate result.
How to Get an Accurate Pregnancy Test
The best way to make sure you get an accurate pregnancy diagnosis is to visit a doctor, clinic, or pregnancy center. These places all have trained and helpful staff who can ensure you take the test correctly and get an accurate result. If you do get a positive test, you can also follow up with an ultrasound to ensure your pregnancy is healthy and viable.
At Pregnancy Care Center of Grants Pass, we offer free pregnancy testing and free limited OB ultrasound examinations to provide accurate pregnancy test results in a simple, safe and convenient way. We also offer free educational resources and information on parenting, adoption, and abortion, as well as our Pathways class, which helps prepare men and women for successfully navigating pregnancy and early parenthood. Call us today at (541) 479-6264 or visit our website to schedule an appointment at our center and get your questions answered.
The truth about getting a false positive on your pregnancy test
You’ve taken a pregnancy test and you see a positive result, but you’re having doubts: Can the test be wrong? Most home pregnancy tests are reliable, for example Clearblue’s tests have an accuracy of over 99% from the day you expect your period, and while it’s possible a test showing a negative result is wrong, particularly if you’re testing early, getting a false positive is extremely rare. Saying that, there are exceptions when your test may come out positive and you are not pregnant, read on to learn about the truth behind false positives.
- A pregnancy test works by detecting the hCG hormone, which is usually only present in your body if you’re pregnant.
- A positive pregnancy test result will mean you are almost certainly pregnant.
- Getting a true false positive – when you were never pregnant in the first place – is incredibly rare.
- A test will only show a false positive if you have hCG in your system for another reason such as you were recently pregnant, are taking fertility medications containing hCG, or if you have a medical condition, like some rare ovarian cysts.
- If you are testing before the date of your expected period, you may be pregnant but your hCG levels are too low for the test to detect.
- A test may show positive if you have a chemical pregnancy (early pregnancy loss), an ectopic pregnancy, or a molar pregnancy, but this is not a false positive.
What can cause a false positive?
Getting a true false positive – one where you were never pregnant in the first place – is incredibly rare. Pregnancy tests detect the hCG (human Chorionic Gonadotrophin) hormone in your body, which is only present when you’re pregnant. This is why a positive pregnancy test result will mean you are almost certainly pregnant.
However, in rare instances, you can get a false positive from:
- a recent pregnancy (e.g. after miscarriage, recent birth or termination)
- some rare ovarian cysts
- certain medications containing the hCG hormone, like some fertility treatments
However, there are cases when you may get a positive result and then find out later you are no longer pregnant – but you were. This can happen if you had a chemical pregnancy or early loss, or an ectopic pregnancy. These are not false positives – they are true positive pregnancy results even though the pregnancy doesn’t continue.
What is a chemical pregnancy?
A chemical pregnancy is a very early pregnancy loss that happens just after the embryo implants. An ultrasound wouldn’t detect a fetus, but your body produces the hCG hormone so the result would be positive. Unless you took a pregnancy test, you wouldn’t know you had been pregnant, as a chemical pregnancy will show very few symptoms, and you wouldn’t experience pregnancy-related signs like morning sickness. Many experts think that chemical pregnancies occur for similar reasons as many other miscarriages – due to chromosomal problems with the developing baby.
Watch our video to learn about what is a chemical pregnancy and why it shows up positive on your test. Early pregnancy loss is common – it occurs for around 1 in 4 women – but most women who lose a baby can still go onto have a healthy pregnancy.
What is an ectopic pregnancy?
An ectopic pregnancy is a relatively rare condition (affecting around 1 in 90 pregnancies) where a fertilized egg implants outside the uterus, such as in the fallopian tube. It can be risky to your health if the pregnancy continues and it’s not possible to save the pregnancy. Symptoms of an ectopic pregnancy include:
- a missed period
- pain low down on your tummy to one side
- pain in the tip of your shoulder
- vaginal bleeding or brown, watery discharge
- discomfort on the toilet
These symptoms can be caused by other things such as tummy upset, but if you are pregnant and have any of these symptoms you should seek urgent medical advice as a precaution.
What is a molar pregnancy?
You may test positive if you have a molar pregnancy. A molar pregnancy is a very rare complication that occurs during the very early stages of fertilization that causes the fetus to develop abnormally. In a full molar pregnancy – when all the genetic material from the mother is lost during fertilization – there is no baby. Instead, a mole, a cluster of abnormal cells that grow into cysts, form. You can read about a molar pregnancy in more detail here. A molar pregnancy will also show up as a positive result since your body is producing hCG and is not a false positive result.
Can I get a positive result after a recent pregnancy, miscarriage, or termination?
Yes, but only some. Taking antibiotics won’t make your pregnancy test positive, but if you’re on fertility medications, containing hCG (these are given by injection) you may get a false positive result. These drugs include:
- Novarel® (Ferring B.V.)
- Pregnyl® (Merck)
- Ovidrel® (Merck)
- Profasi® is a registered trade mark of Ares Trading S.A
Most medications you have in your medicine cabinet, such as painkillers, antacids, etc. will not affect the result of a home pregnancy test.
What medical conditions could give me a false positive?
In some rare instances, certain medical conditions can cause a rise in hCG levels, even when you’re not pregnant. These include:
- ovarian cysts
- kidney disease
- certain cancers
- disorders that affect hormone levels, particularly in menopausal or peri-menopausal women
- tumors of the cells that would make up the placenta
Is It Possible to Get a False Positive Pregnancy Test Result?
Home pregnancy tests are pretty reliable — in fact, most of them can detect a pregnancy with 97 percent accuracy as early as the day after you miss your menstrual period. The tests work by indicating whether or not there’s a pregnancy hormone called human chorionic gonadotropin (hCG) in your urine. If you’ve got a measurable level of hCG, congratulations! You’re pregnant — with these few, rare exceptions.
The most common explanation for a “false positive” is that you really were pregnant when you took the test. “Some women can get a positive pregnancy test and then three days after their period is due, they have a really heavy period,” says Lanalee Araba Sam, M.D., an ob-gyn in Fort Lauderdale. “Really what they’ve had is an early miscarriage called a chemical pregnancy, and a lot of people call that a false positive. They don’t recognize it as a positive pregnancy test that ultimately results in miscarriage.” Dr. Sam explains that as many as 25 to 40 percent of pregnancies may end as an early often-undetected miscarriage. Some women don’t even know they’re pregnant in the first place.
- Wondering if you’re pregnant? Take our quiz!
Once you get your positive pregnancy test result, call your doctor and make an appointment. It may be many weeks away, and it can be stressful to wait for acknowledgment that everything’s okay with your pregnancy. But, Dr. Sam explains, an ultrasound can’t help your doctor see the gestational sac until about 6 weeks, and can’t detect a fetus with a heartbeat until around 6 or 7 weeks. Once you see that heartbeat, your chance of miscarriage plummets to less than 5 percent.
In the meantime, look out for heavy bleeding or intense cramping, and call your doctor right away if you experience either of them.
- Shop for at-home pregnancy tests
If you’ve had a miscarriage, hCG can stay in your bloodstream for several weeks afterward, or until your period returns, says Dr. Sam.
Pregnancy test errors
Check your pregnancy test kit to make sure it hasn’t expired, and follow the instructions carefully. Making a mistake can affect the reliability of the test results.
As part of infertility treatments, some women receive hCG injections to cause them to ovulate. If you’re one of them, your doctor will advise you on how to accurately test for pregnancy.
Other medications, such as methadone, could also interfere with pregnancy test accuracy, says Sean Daneshmand, M.D., an ob-gyn based in San Diego and founder of the nonprofit organization Miracle Babies.
In some instances, tumors in the body can produce hCG. This is the case for certain ovarian germ cell tumors and gestational trophoblastic disease, a rare condition in which the cells that normally form the placenta develop tumors instead, says Dr. Daneshmand.
The bottom line is this: If you had a positive pregnancy test, it’s 97 percent certain that you’re pregnant.
Copyright © 2015 Meredith Corporation.
All content on this Web site, including medical opinion and any other health-related information, is for informational purposes only and should not be considered to be a specific diagnosis or treatment plan for any individual situation. Use of this site and the information contained herein does not create a doctor-patient relationship. Always seek the direct advice of your own doctor in connection with any questions or issues you may have regarding your own health or the health of others.
- By Elena Donovan Mauer
At-home pregnancy tests are pretty damn accurate. If you get a positive result you can almost certainly assume you are pregnant, at which point you should visit your GP to confirm the news, and then you can spend the next nine or so months cooking your human child.
But on some rare, and we mean very rare occasions, your test might display a false result. This could either be in the form of a ‘false positive’ – a test that says you’re pregnant when you don’t actually have a viable pregnancy, or it could be in the form of a ‘false negative’ – a negative result when you are, in fact, pregnant. We asked Dr Preethi Daniel, Medical Director at London Doctors Clinic to talk us through all the ways either of these eventualities could happen:
1. Expired pregnancy test
“Pregnancy tests expire, which can result in a false-negative test. Heat or moisture can cause damage to the test window on a pregnancy test and this can also result in inaccurate results. If you want to buy a pregnancy test, go to the pharmacy so you can guarantee it’s within date.”
2. Fertility medication
“HCG (or if you want to get technical, human chorionic gonadotrophin) is a hormone released by the placenta after the embryo has been implanted into the womb. This hormone can be detected in the woman’s urine or blood even before a missed period. But if you’ve been going through fertility treatment, like IVF for example, and you are given fertility medication, this can cause a false positive reading on a pregnancy test. Fertility treatments are hormones which may mimic or even contain HCG, which is why this may happen.”
“If you have had a recent miscarriage, the HCG level can stay in your bloodstream for a number of days. This can result in a false positive test result.”
“Some medications can alter the level of HCG in the blood. These include benzodiazepines taken for anxiety (diazepam, alprazolam), diuretics taken for excess water retention (furosemide) and even antihistamines such as promethazine.
“These medications could theoretically lead to a false positive result if a woman has experienced either a chemical pregnancy (more on that below) or a miscarriage, both of which would leave a small, undetectable level of HCG in the woman’s bloodstream. The medication could increase this level slightly, bringing it into a detectable range, hence the possibility of a false positive result emerging from the test.”
5. Chemical pregnancy
“This is where a sperm and an egg meet but the fertilised egg – known as an embryo – is unable to implant in the womb. This can still cause a rise in HCG levels despite there being no viable pregnancy. For some woman, this false positive result can be emotionally draining. It’s for this reason it is always recommended you wait a week or so after you miss your period to take a pregnancy test.”
6. Ectopic pregnancy
“An ectopic pregnancy can result in a positive reading on a pregnancy test, and this does indeed mean you are pregnant. Sadly, though, this pregnancy is not in the right place. The foetus is most likely in one of your fallopian tubes (the tubes that carry the egg to the womb) and this is a medical emergency. If you have a positive test result at home and start experiencing abdominal pain, bleeding or are feeling unwell, it’s vital you see a doctor as soon as possible.”
An ectopic pregnancy is where the pregnancy occurs in the fallopian tube instead of the womb. Getty Images
7. You’ve left the test sitting too long before looking
“You’ve urinated on the stick, and are now eagerly awaiting. You might want to take your mind off the nervous wait, but don’t wander off and forget; leaving the test ‘cooking’ for too long can give a false positive result. The reason for this is due to the urine evaporating if left for too long; it can leave a faint line which can be mistaken as a positive test. Its recommended to not read a pregnancy test after the recommended time frame (10 minutes) as most brands have a possibility of evaporation lines.”
8. Medical conditions
“There are certain medical conditions that can impact the outcome of a pregnancy test. If you’re suffering from a urinary tract infection, kidney disease or have ovarian cysts, this may alter the result of your test:
- Urinary tract infection or kidney disease may result in a contaminated sample (with red or white blood cells in your urine) which may result in a false positive result. It does depend on the method used by individual brands but in general any impurity or even blood can cause a false reading.
- Ovarian cysts/cancer or disorders of the pituitary gland (in the brain) can either produce HCG leading to a false result or produce hormones mimicking HCG, once again leading to a false positive. These cancers often produce small amounts of the hormone, but home pregnancy tests can be sensitive enough to pick this up.”
Dr Preethi was keen to reiterate that “home pregnancy tests have advanced considerably in the technology they use and, with rigorous testing, have increased in accuracy over the years.” But she does suggest that if you want to make sure you’ve got the absolute best chance of accuracy, do the test in the morning. “Catching your first urine of the day ensures HCG levels are at their highest,” she said.
Related Story Catriona Harvey-Jenner Digital Features Editor Cat is Cosmopolitan UK’s features editor covering women’s issues, health and current affairs.
Houston Fertility Journal
You tried and tried, and finally achieved what you’ve been working towards and hoping for. A positive pregnancy test. You go to the doctor overjoyed, but cautious. You want to be sure this is really happening. Just one little problem. You’re not actually pregnant. What really happened was you had a false positive pregnancy test.
When you’re already struggling to achieve pregnancy, few things can be as devastating as a false positive. You might be wondering what causes a false pregnancy test to happen.
Today we’ll explore:
- All the things that can lead to a false positive
- What to look for if you think you might be pregnant
- How to know for sure whether or not you are actually pregnant
- And more…
The most common causes The Most Common Causes of a False Positive Pregnancy Test
For something that seems so black and white, people often wonder what can cause a false positive pregnancy test. Some of the most common causes are:
- The pregnancy test being expired
- Letting the test sit too long before checking it
- Having a miscarriage or “chemical pregnancy”
- Being on certain medications
- Having an ectopic or molar pregnancy
- Other medical conditions
- A faulty pregnancy test unit and/or
- Contaminated samples
An expired pregnancy test can yield a false positive
The way that over-the-counter pregnancy tests (also called home pregnancy tests) work, is that they indicate whether or not your urine contains the human chorionic gonadotropin (hCG), or pregnancy hormone. When a pregnancy test is past its expiration date, the chemicals that are inside it don’t work the way that they’re supposed to.
Therefore, an expired pregnancy test can misread whether or not your urine contains hCG. Your best bet to avoid this false positive, is to ensure that the test you are taking is not expired. Regardless of where you get it, be sure to check the expiration date that is listed on the packaging before use.
And as a side note, don’t assume that the test you are taking is better or worse than any other based on its price or brand. For example, according to momjunction.com, the tests that you can purchase at dollar stores like Dollar General, were just as effective in indicating whether or not a pregnancy existed, as those of the higher-priced brands found at most big-box stores (Walmart or Target), and convenience stores (Walgreens, CVS, or Rite-Aid).
What they found: “This test kit is 99% accurate but is not ultra-sensitive in detecting hCG. So, it will not detect low levels of the hormone that are present in your body after fertilization occurs. This is the reason you should wait a few days after missing your period before using the kit. Most experts agree that you get the most accurate results when your period is a week late.”
Don’t let the test sit too long after completion before checking the results
The directions on the box are there for a reason. When you allow a test to sit by itself for too long after you’ve completed it, the urine that is on the test can evaporate. As this urine evaporates the test results can be distorted. In fact, one line can suddenly appear as two, or a negative can look like a positive depending on the test you’re taking.
Read all instructions carefully and follow them to the letter. If it says leave the dipstick in the urine for two minutes, for example, take it out at the two minute mark. If the results are available in 10 minutes, don’t wait 20 to check them. You get the idea. Failure to follow the instructions explicitly is one thing can result in a false positive pregnancy test.
Having a miscarriage or “chemical pregnancy” can lead to a false positive
For an otherwise healthy woman, she is most susceptible to a miscarriage within the first 12 weeks. A miscarriage is the term used to describe a pregnancy that ends within the first 20 weeks of gestation. However, most miscarriages actually occur in the first 13 weeks, and many women who have a miscarriage never knew they were pregnant in the first place.
What is a chemical pregnancy? According to the American Pregnancy Association, “Chemical pregnancies may account for 50-75% of all miscarriages. This occurs when a pregnancy is lost shortly after implantation, resulting in bleeding that occurs around the time of her expected period. The woman may not realize that she conceived when she experiences a chemical pregnancy.”
What causes the false positive in this case is that you still had some hCG in your system when you took the pregnancy test. This is one of the reasons that many experts advise against early detection tests. While chemically speaking the tests are not necessarily wrong in detecting hCG, you may no longer be pregnant when you take the test, unfortunately.
Certain medications can distort pregnancy test results
Taking a drug containing hCG can cause a false positive pregnancy test. It takes between one and two weeks for an injection of it to clear your system, depending on the number of units you are prescribed. Therefore, if you are taking injections of hCG as part of your fertility treatments, you would be better off waiting until that period has expired prior to attempting a pregnancy test.
Other medications that have been found to cause a false positive pregnancy test include:
- Psychiatric medications such as anti-anxiety (like Xanax and Valium), and antipsychotic prescriptions (like clozapine or chlorpromazine)
- Medications prescribed for Parkinson’s disease
- Phenergan and other anti-nausea medications
Effectively, any medication that messes with your body’s chemical makeup, or leaves traces in your urine, could potentially distort a urine test.
Having a molar or ectopic pregnancy
In an ectopic pregnancy, a fertilized egg will implant itself somewhere other than the uterus. The most common place is in the fallopian tube, but it can also occur in the ovary, abdominal cavity or the cervix. Because there is a fertilized egg, hCG will be present in the system, resulting in the false positive pregnancy test.
When an ectopic pregnancy occurs, swift treatment is required to halt the implanted egg’s development. Not doing so can cause significant complications for a woman including loss of reproductive organs, and/or extreme blood loss.
The symptoms of ectopic pregnancy are:
- Pressure on the rectum
- Dizziness, and feeling faint, or even fainting
- Severe pain on just one side of your abdomen, or in your pelvis, neck and/or shoulders
- Tender breasts and nausea
It’s important to note that many of these symptoms can be a sign of a regular pregnancy. On the other hand, if you experience one or more along with the other symptoms, it could be cause for concern. If you even remotely suspect you could be suffering from ectopic pregnancy, do not hesitate. Seek medical attention at once because an ectopic pregnancy is a medical emergency that will only worsen, and can not be managed on its own.
A molar pregnancy occurs when the fertilization process leads to the growth of abnormal tissue within the uterus. Molar pregnancies rarely involve a developing embryo, but they often entail the commonly known symptoms of pregnancy including a missed period, and severe nausea. With molar pregnancies, hCG is also present in the body, and can therefore lead to a false positive as well.
Other medical conditions that can cause a false positive include:
- Urinary tract infection (or UTI)
- Ovarian cysts and/or ovarian cancer
- Cancer in the bladder, kidney, lung, colon, breast, liver or stomach
- Pituitary gland problems, or disorders affecting your hormone levels (although these are rare, they do occur)
- Blood or white blood cells in the urine stream as a result of kidney diseases or infections
- Residual hCG in your system from a previous birth, miscarriage, abortion, diet injection programs, or fertility treatments
- Tumors that produce hCG (again, this is rare, but could happen with things like ovarian germ cell tumors and gestational trophoblastic disease)
Your pregnancy test unit was faulty
It’s no secret that pregnancy test units, and their packaging, are mass-produced in factories. Therefore, it stands to reason that one in hundred, or a thousand or even a million could be faulty. While there is no way to guarantee that your test is in perfect condition, that random chance of a faulty test can cause an inaccurate result. It’s one of the reasons that experts agree you should not rely on a single test to determine whether or not you’re pregnant.
Your urine sample was contaminated
In some cases, albeit rare ones, a contaminated urine sample can lead to a false positive pregnancy test. Some experts believe that soap, detergents and/or blood in the urine can lead to distorted results. The best best for avoiding this false positive is to use a clean sample and sterile conditions.
For example, if you have to urinate into a cup and then pour it onto the test, you must ensure the cup is sterile, and has no soap/detergents in it. Or, as mentioned above, if you have a kidney disease or an infection such as a urinary tract infection, it can cause blood to be present in your urine which can also affect the test results.
Is There Such Thing As a False Negative Pregnancy Test?
If there can be a false positive pregnancy test, you may be wondering if there is such a thing as a false negative pregnancy test as well. Yes. Believe it or not, false negatives can and do occur. Here’s a breakdown of what results can come from a pregnancy test:
- In the event that you have a false negative pregnancy test, what that means is your test was negative, however you are in fact pregnant.
- A false positive indicates that you’re pregnant even when you are not.
- A true positive pregnancy test indicates that your pregnant and your results on the test show up as positive.
- A true negative pregnancy test, just like it sounds, indicates that you are not pregnant, and the test results were also negative.
How can you know for sure whether or not you are actually pregnant?
Whether you’ve experienced a false positive pregnancy test or are just curious, at some point you will likely want confirmation as to whether or not you are pregnant. Here are a few symptoms to look for that may help you determine your status:
- Missed period – perhaps the most common symptom of all pregnancy symptoms
- A sudden aversion to or craving for certain foods and/or all food
- A heightened sense of smell
- Sudden onset fatigue, or increased fatigue compared with previous levels
- More frequent than usual urination
- Tender, swollen, or sore breasts (some women even experience tingling, and say their breasts feel heavier or more full)
- Nausea and upset stomach
- Dizziness and feeling faint or even fainting
- Mood swings
- Higher than normal body temperature
- Headaches and lower back pains
All symptoms and assumptions aside, however, you’ll ultimately need to visit your doctor for unequivocal proof of pregnancy.
When you’re ready to visit a doctor, let them know you would like a pregnancy test. They can do one of four things at this point:
- A urine test
- A blood test (considered more reliable than a urine test, and can detect a pregnancy earlier than a urine test will)
- An internal examination (your doctor can perform an internal examination to look for changes to the cervix and uterus. For example, your cervix can change color and become softer, and your uterus can expand even in the first few weeks of pregnancy.)
- All of the above
When should you take a test?
Most doctors and experts agree that you should wait until one full week after your first missed period to take a pregnancy test. Then again, this is the earliest point at which you should test.
Remember, most miscarriages can occur within the first 13 weeks. It’s important to keep in mind that even if you visit with your doctor and learn you are pregnant, this is not a medical guarantee you will be able to bring the pregnancy to term.
In many cases, reading an article like this can leave people with more questions than answers. We understand that every medical case is different, and you may want to learn more about topics like how best to go about achieving pregnancy, what can lead to miscarriage, causes of infertility, and a variety of other subjects. Check out our blog to answer many of our frequently asked questions.
How do pregnancy tests work?
Pregnancy tests are an easy and accurate way to find out if you’re pregnant — you just pee on a stick. They’re inexpensive and available at most drug and grocery stores.
How accurate are pregnancy tests?
Pregnancy tests are super accurate when you use them correctly. The pregnancy tests you get at the drugstore work 99 out of 100 times. They’re just as accurate as a urine pregnancy test that you’d get at a doctor’s office.
Pregnancy tests work by checking your urine (pee) for a hormone called human chorionic gonadotropin (HCG). Your body only makes this hormone if you’re pregnant. HCG is released when a fertilized egg attaches to the lining of your uterus — when pregnancy begins. If your pregnancy test results are positive, it means you’re pregnant. If they’re negative, it means you’re not pregnant.
Pregnancy tests are most accurate when you take them after you’ve already missed your period.
A pregnancy test will be less accurate if it’s expired or if you don’t use it the right way. So always check the expiration date on the package, and carefully read the directions that come with your pregnancy test.
How soon can I take a pregnancy test?
You can take a pregnancy test anytime after your period is late — that’s when they work the best. It’s a good idea to take a pregnancy test as soon as possible if you miss your period or think you might be pregnant.
The earlier you know you’re pregnant, the sooner you can start thinking about your options and get whatever care you need to stay healthy.
Many pregnancy tests say they work a few days before a missed period, but the results are usually less accurate then. Read the label on your pregnancy test to find out when to take a pregnancy test and how accurate it’ll be.
Sometimes a pregnancy test is able to find pregnancy hormones in your urine as early as 10 days after unprotected sex. But these results aren’t super reliable, and you may get a false positive or false negative test result.
If your periods are very irregular, or you don’t get periods at all for one reason or another, your best bet for accurate results is to take a pregnancy test 3 weeks after sex.
Where can I get a pregnancy test?
You can buy a pregnancy test at your local pharmacy, drugstore, grocery store, and some convenience or dollar stores. Pregnancy tests are usually inexpensive — they can cost as little as a dollar. Sometimes you can get a free pregnancy test at certain health centers.
You can also get a pregnancy test from your nurse or doctor, community clinic, or local Planned Parenthood Health Center. Most health centers use the same urine pregnancy tests that you can buy in stores. Sometimes they use a blood test to test for pregnancy, but that’s usually only under special circumstances.
But be careful when looking for a reliable health center, because there are fake clinics out there called Crisis Pregnancy Centers. Crisis Pregnancy Centers give free pregnancy tests and claim to offer information and help. But they’re run by people who may not be medical professionals, and don’t believe in giving you honest facts about pregnancy and all of your options. Crisis pregnancy centers are often located very close to Planned Parenthood health centers or other real medical centers, and have similar names — they do this to confuse people and trick them into visiting their center instead.
Your nearest Planned Parenthood health center can help you find a safe place to get a pregnancy test in your area.
What should I do if my pregnancy test is positive?
If you take a pregnancy test after you miss your period and the result is positive, that means you’re pregnant. You can always take another test to be sure, if you want.
You may want to go to a nurse or doctor, family planning clinic, or local Planned Parenthood Health Center to get a follow-up test. They’ll talk with you about your pregnancy options, and help get you the care you need. Be careful not to visit a Crisis Pregnancy Center, because they might not give you real medical care or truthful information about your pregnancy and all of your options.
More questions from patients:
What’s a false positive pregnancy test?
A false positive pregnancy test is when you get a positive result from a home pregnancy test but you’re not really pregnant.
A false positive result means that the pregnancy test detected the hormone hCG in your pee. For this to happen, either the test didn’t work right or you had hCG in your body for another reason. These could include:
taking the test too soon after taking fertility drugs that contain the hormone hCG
having an ectopic pregnancy or miscarriage
If you have a positive pregnancy test, visit your doctor, midwife, or local Planned Parenthood health center. They can determine if you’re really pregnant and help you with next steps.
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False Negative Pregnancy Test: How to Identify the Hook Effect
False negative results can be stressful part of your initial steps in pregnancy. You’re sure that you’re pregnant because you recently had a positive pregnancy test, but now a few weeks later, you see a faint pregnancy test line or no line at all. Should you worry?
If you take a pregnancy test after about week five of pregnancy, you might experience a type of false negative called the hook effect. To explain why this happens, this post will cover how a pregnancy test works, what the hook effect is, and what you can do.
How does a home pregnancy test work?
A home pregnancy test measures amount of hCG in your urine. This type of a test is a sandwich enzyme immunoassay. It sounds complicated, and the chemistry of it is, but if you’ve made a peanut butter and jelly sandwich before, then you’ll understand how this test works.
HCG is a really big molecule that is made of two parts: the alpha part and the beta part. Let’s call the alpha unit of hCG “the peanut butter” and the beta unit “the grape jelly”. To detect both parts of hCG, a pregnancy test loads the stick with two different antibodies—let’s call them “the bread slices”. The first antibody gloms on to the alpha unit (“peanut butter”) and the second antibody gloms on to the beta unit (“the grape jelly”), which forms a chemical sandwich.
Once hCG is successfully sandwiched, when you take a pregnancy test this triggers release of a dye—that’s the dark line on a pregnancy test that means you’re pregnant! The first line on a pregnancy test is a control test that simply makes sure the antibodies and dye are working.
Why can I get a positive pregnancy test then negative?
There are two reasons why you would get a positive pregnancy test and then a negative:
- Miscarriage/chemical pregnancy: With a miscarriage, hCG levels rise and then drop back down. As hCG levels decrease, you will notice the second line on a pregnancy tests getting lighter or disappearing completely.
- The hook effect: As your pregnancy progresses, changes in the type of hCG can cause false negative pregnancy test results. Read on to understand how and why this occurs.
You might expect that because the further along in pregnancy, the darker the line on your pregnancy test. But this is not the case, and it’s because of the antibodies loaded in the pregnancy test.
Just as you can have other variations of peanut butter and jelly sandwiches besides the one with classic grape jelly—say, with strawberry jam—there are also variations of hCG. Why does this matter? The relative amounts of these different variations change over the course of pregnancy, and this messes with the antibodies in your pregnancy test.
Pregnancy tests are good at measuring intact hCG—or when there’s peanut butter AND grape jelly—which is great during the first few weeks of pregnancy. However, around week five, the dominant form of hCG in your urine is hCG-βCF, which is a version of hCG that is all beta unit and no alpha, or all strawberry jam and no peanut butter.
That’s a problem for a pregnancy test. The test gets overwhelmed with all the beta fragments (or strawberry jam), which interferes with test’s ability to find intact hCG (or peanut butter and grape jelly).
Instead of a linear relationship where the line gets darker the more pregnant you are, the pattern actually looks more like a hook or curve, with a darkening line from weeks three to five of pregnancy, then a fading line thereafter.
This means it’s possible to get a positive pregnancy test, and then a few weeks later get a negative one—even though you’re still pregnant! Scientists have even tested this by taking a positive urine sample, immediately adding pure hCG-βCF, and then observing a negative result.
How can you tell if you’re experiencing the hook effect?
The hook effect can cause someone who has a healthy, normal pregnancy to get a negative pregnancy test. If you get a negative pregnancy test after a positive, how can you tell if it’s the hook effect?
There’s a simple test: all you have to do is dilute your urine, which prevents hCG-βCF excess. Here’s how:
- Collect your urine in a cup
- Dilute your urine with an equal quantity of water
- Re-take a pregnancy test using the diluted urine
- If you are experiencing the hook effect, the pregnancy test using diluted urine will be darker
Read more about pregnancy tests:
Should you take a pregnancy test?
Period late, but negative pregnancy test?
What’s the best pregnancy test?
By Aarthi Gobinath, PhD | Mar 9, 2018 Tags: early pregnancy, early pregnancy symptoms, hormones, pregnancy
Aarthi Gobinath, PhD
Aarthi Gobinath earned her PhD in neuroscience from the University of British Columbia. Her research covers the ways that stress affects the male and female brain differently.
Home pregnancy tests are very accurate if you use them correctly
- There are two types of at-home pregnancy tests. Both are 99% accurate if you take them in a lab setting, like at your doctor’s office. If you take the test at home, the accuracy can be lower than 99%.
- Interpreting the results of a home pregnancy test can be tricky. One way to overcome any confusion is to use a digital test in which the results are displayed as “pregnant” or “not pregnant.”
- There are many ways where you can get an inaccurate reading from a home pregnancy test like if you use an expired test or you wait too long to read the results.
- This article was reviewed by Karen Duncan, MD, who is an assistant professor with the Department of Obstetrics and Gynecology at NYU Langone.
- Visit Insider’s homepage for more stories.
There are dozens of home pregnancy tests on the market, which can make it confusing to determine which is best.
Here’s what you need to know about the accuracy of home pregnancy tests — and how to deal with an inaccurate result.
Home pregnancy tests can be 99% accurate
There are two basic types of home pregnancy tests. Both test for the presence of the pregnancy hormone hCG (human chorionic gonadotropin). The difference is that one uses a test strip or dipstick that you hold in the urine stream and the other uses a urine collection cup with a test device.
When you take either of these tests in a lab setting, like at your doctor’s office, both are close to 99% accurate. But when you perform them at home, the accuracy drops because people fail to follow instructions or they take the test too soon, according to Dr. Jane van Dis, MD, FACOG, an OB-GYN and medical director at the Maven Clinic.
Even when the instructions are followed correctly, interpreting the results can be tricky. One way to overcome any confusion is to use a digital test in which the results are displayed as “pregnant” or “not pregnant.” Though these tests can be more expensive — often costing $8 per test compared to $3 for your standard dipstick or cup test, depending on the brand.
Another important caveat is whether the test is expired. Many people don’t realize that pregnancy tests can expire, so check the expiration date before using it. The chemical that detects hCG levels won’t work as well after the expiration date, making it less accurate and more likely to give you a false-negative result.
Common causes of false results
A false-negative result occurs when the test result is negative but you are indeed pregnant. This often happens when the test is taken too early or incorrectly and your hCG levels aren’t yet high enough to be detected in a urine sample, says Kenneth Ward, a lab director, scientific adviser, and a medical geneticist at Predictive Laboratories.
Waiting until the day of your missed period or later will result in a more accurate reading. Moreover, take the test first thing in the morning, since that’s when your urine is likely to have more concentrated levels of hCG, because you’re more dehydrated.
A false-positive, on the other hand, occurs when the test says you are pregnant but you are not. One rare cause of a false-positive is ovarian tumors, but a more common culprit is an abnormal pregnancy that results in an early loss.
Chemical pregnancies, for example, can result in a false-positive because the pregnancy can produce a detectable level of hCG, but then the embryo is lost or miscarried.
Most foods or common drugs will not affect test results, but fertility medications that include the hCG hormone to induce ovulation can also result in a false-positive, Ward says.
Another cause of a false-positive or false-negative is not reading the results within the designated time frame.
“If you wait too long, you can have a positive turn negative, or vice versa,” Ward says.
What to do next
If you get a negative test result, take another test in a few days. If you’re early on in your pregnancy, your hCG levels should double every 48 hours, increasing your chances of an accurate reading. If you suspect you’re pregnant but tests keep saying you’re not, talk to your doctor.
If you get a positive test result, contact your doctor, and consider the home test a first step in the process of determining pregnancy.
“You need to make sure your test is followed up by a continuing rise in hormone levels, and will want to have an early pregnancy ultrasound to confirm,” Ward says. “Within a few weeks, you’ll see the heartbeat, which is the true confirmation.”
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