Pregnancy Tests: A Brief TutorialTo understand why you might get a false positive or a false negative pregnancy test, you must first understand how pregnancy tests work. Pregnancy tests measure levels of human chorionic gonadotropin (HCG). This is a hormone that the body begins secreting when an embryo implants in the lining of the uterus. Implantation is therefore the medical beginning of pregnancy. Women commonly have very low levels of HCG even when they’re not pregnant. So pregnancy tests detect HCG levels that are higher than usual, since higher HCG usually means a woman is pregnant. HCG levels at the moment of implantation are very low, but they quickly double, and then triple, and then rise exponentially thereafter. So whether or not a pregnancy test can detect pregnancy depends on how much HCG a woman is producing. More sensitive tests can detect lower levels of HCG, and will therefore give a positive result earlier in a woman’s pregnancy. A false negative pregnancy test is more common than false positive because a woman may get a negative test when HCG levels are too low. Very few things can mimic HCG, however, so as long as a pregnancy test is working correctly, the odds of a false positive test are virtually zero. It's a myth that a woman is pregnant at the moment of fertilization, or that a test can be positive as soon as the egg is fertilized. So testing a few days after having sex or ovulating will almost always produce a negative test result, even if the egg has been fertilized and the woman will soon test as pregnant.
False Negative Pregnancy Test: What Causes It?False negative tests are common. In fact, many women get false negative tests before they get a positive. This is because the body’s HCG levels have not yet risen sufficiently high to indicate that a woman is pregnant. In many cases, a woman will later get a positive test if she just waits a few days. The most common reasons for false negative pregnancy tests include:
- Not getting enough urine on the test.
- Not using urine that is sufficiently highly concentrated. Especially in the earliest days, it’s best to use the first morning’s urine. This urine tends to be more concentrated, and therefore has more easily detected HCG levels.
- Testing too early.
- HCG levels that are not rising rapidly enough. Sometimes a woman is pregnant, but her body does not have sufficiently high HCG levels to sustain the pregnancy.
- A test that is expired or otherwise defective.
- Not following the test instructions, such as by checking the test too early or late.
- Getting too much urine on the test stick, since this may affect the results and dilute a positive.
- Not correctly reading the test result. Even the faintest positive is still positive. If there is any line visible at all, read the test as positive.
- Testing at the wrong time. Some women chart their period only by counting days on a calendar. If your periods are irregular, you might have the dates wrong. Instead, it’s better to monitor your cycles, measure the day you likely ovulated on, and then test at least 10 days after this date.
- Using a pregnancy test that is not sufficiently sensitive. Some pregnancy tests can only detect HCG at very high levels -- levels that only occur several days into pregnancy. Read the test insert to determine how sensitive the test is. For the earliest possible positive result, pick the most sensitive test. This means selecting the test with the ability to detect very low levels of HCG.
False Positive Pregnancy Test: What Causes It?To get a positive pregnancy test, many factors have to come into play. Like a perfectly orchestrated symphony, it’s easy for one component to be out of tune. That’s why false negatives are much more common than false positives. Even when a woman is pregnant, she might not get a positive result. To get a positive test, a woman must:
- Use a sufficiently sensitive test.
- Test at the right time during her cycle.
- Test only after implantation.
- Have HCG levels that are rising.
- Correctly read the test, since even a faint positive is still a positive.
- Allowing a test to sit for too long. This can cause an evaporation line that may look like a faint positive.
- Using an expired test. This can cause a positive line to appear even if the test is not positive.
- Having a chemical pregnancy. When this happens, the woman is pregnant, but has an early miscarriage.
- A recent miscarriage. HCG levels take a while to drop following a miscarriage. A woman who has recently had a miscarriage may still test positive on a pregnancy test.
- Taking certain fertility medications. Fertility medications that raise HCG or that are chemically similar to HCG can cause a false positive. Talk to a doctor if you take fertility medications, since a home pregnancy test might be less accurate.
What if I Get Both a Positive and a Negative Pregnancy Test?Some women get a negative test, and then later test positive for pregnancy. If this happens, believe the positive test. That’s because HCG levels take a while to rise, and the positive test may be because they’re finally high enough for a test to register. If one test is positive and one test is negative, the best option is to wait a few days. Then take a third test. If that test is positive, you are probably pregnant. If the test is negative, or you continue to get a mix of positive and negative pregnancy tests, it could mean you are having a miscarriageor that your HCG levels are very low. Call your doctor. Your doctor can perform blood work to assess HCG levels and determine whether you are pregnant or not.
What if I get a Positive Test, and then Several Days Later it’s Negative?Sometimes a woman gets a positive test followed by a negative. This sometimes happens when one test is less sensitive than another. But if a positive test is followed by several negative tests, this could mean the woman is having a chemical pregnancy. You might read online that a chemical pregnancy is a pregnancy that never implants, or that it’s not a pregnancy at all. This is not true. Chemical pregnancies are shrouded in mystery and false information, especially online. A chemical pregnancy is in fact no different from any other pregnancy. The only distinction is that it ends with a miscarriage very early -- before an ultrasound can detect a heartbeat and before a doctor confirms pregnancy with an in-office test. A chemical pregnancy is not your fault. Like any other miscarriage, it usually cannot be prevented. In most cases, it happens because there is a genetic anomaly with the embryo that would have made it impossible for the embryo to survive outside of the uterus. That doesn’t make the experience any less painful. You can grieve a chemical pregnancy just like any other miscarriage, and there is no “right” way to feel. The good news is that most women get pregnant soon after having a chemical pregnancy. A single chemical pregnancy does not mean there is anything wrong with your body, or that you are infertile. Because a chemical pregnancy ends so early, many women do not develop other symptoms of pregnancy. But some do. Some signs that you might be having a miscarriage of a chemical pregnancy include:
- Pregnancy symptoms that suddenly go away.
- A pregnancy test that was strongly positive, followed by progressively fainter positives on the same brand of test.
- Bleeding that looks like a period. For some women, the bleeding is slightly heavier.
Ectopic Pregnancies and Pregnancy TestingSome online guides suggest that ectopic pregnancies may cause false negatives. This is partially true, but a bit misleading. An ectopic pregnancy is a pregnancy that grows outside of the uterus. It cannot grow into a healthy or normal baby, and can endanger the woman’s life. So this pregnancy must be removed as soon as possible. Ectopic pregnancies do not develop or implant normally. So HCG levels may not be as high. Some women might get a handful of positive tests as well as one or two negative tests. If a woman experiences other symptoms of an ectopic pregnancy, such as pain in her side, vomiting, dizziness, or intense nausea, it’s important to check for an ectopic pregnancy. Because any pregnancy can be ectopic, it’s important to see a doctor if you have a positive test and think you might be pregnant.
How Soon Should You Test for Pregnancy?The longer you wait to test after you ovulate, the more likely you are to get a positive result. Yet for most women, that two week wait is agonizing. So it’s best to balance the desire to test early with the knowledge that early tests are inherently less reliable. To get the most accurate result, wait until at least eight days past ovulation (DPO). Implantation is extremely unlikely before this point, and even if it happens, HCG levels will not be sufficiently high to produce a positive test. For the most accurate results, wait until 11 days after ovulation, when slightly more than half of women get a positive result. To increase the odds of an accurate result the first time:
- Use a highly sensitive early result pregnancy test. The most expensive tests are not necessarily the most reliable, so read the box to determine how sensitive the test is.
- Test with your first morning’s urine.
- Track your cycle so you know when you ovulated and can test on the right day.
- Precisely follow the test instructions, and do not read the test too early or too late.
When to See a Fertility SpecialistIf you’ve spent months or years dissecting pregnancy tests, googling for pregnancy symptoms, and getting nothing but negative tests, you already know all too well how painful fertility issues can be. The good news is that help is available, and the sooner you seek help, the greater your odds of a successful pregnancy will be. Consider seeking help if:
- You have had two or more chemical pregnancies, or have had two or more negative tests preceded by positive tests.
- You have been trying for longer than a year to get pregnant, and the woman is under 35.
- You have been trying for longer than six months to get pregnant, and the woman is over 35.
- Either partner has a condition that can cause infertility, or has a previous history of infertility.
- The woman does not ovulate, or has very irregular menstrual cycles.
- The woman has had two or more miscarriages in a row.
March 22, 2021 Written by:
When the Pregnancy Test Positive Line Shows up Later
After getting a negative result on a home pregnancy test, it's fair to conclude that you're not pregnant. However, if you happen to glance back at the test later in the day, you may be surprised to see that a positive line has magically appeared. Here are a few reasons why this can happen and what it means.
The instructions on most pregnancy tests will advise you to read the results within a certain window of time. This usually ranges between a couple of minutes up until 10 minutes later. If you see a positive result beyond this time frame, you may be left second-guessing the results.
However, the false-positive reading, in this case, is due to something called an evaporation line. Evaporation lines are not indicative of a true positive result.
Evaporation lines happen when the urine that was on the test area starts to dry. The chemical composition of the urine sample changes due to evaporation. As a result, the test may start to display a positive line. After the allotted time has passed, you should discard the pregnancy test to avoid confusion.
Faint Test Lines
If you follow all of the instructions correctly, you may notice a thin, faint test line that appears within a few minutes. It can seem at first that the line is too faint to count, but after 10 minutes, it darkens. There are several possible explanations for this faint line:
- Chemical pregnancy: When implantation of a fertilized egg happens, hCG is produced, even though that egg may not be viable. Chemical pregnancies are the most common cause of early miscarriage. Without taking a pregnancy test, the miscarriage may easily be mistaken for a regular period.
- Lower sensitivity test:You might need a test with higher sensitivity levels so that you can get accurate results earlier in the pregnancy. Look for "early results" indicated on the test label.
- Too early in your cycle: If you test earlier than 10 to 12 days past ovulation, the hCG hormone may not be high enough to produce more than a very faint line. The best time to test is after your period is late, or 2 weeks after you ovulated.
- Too much fluid: You can dilute your urine sample if you are urinating too frequently or drinking too many liquids—this is why first-morning urine samples are recommended for pregnancy testing.
If you are still unsure about pregnancy test results, try waiting a day or two to take another test. Always use a sample from your first-morning urine (which is more likely to have higher concentrations of the pregnancy hormone, hCG).
A Word From Verywell
It can very stressful to see conflicting results on a pregnancy test, such as faint lines or evaporation lines. If you're unsure about your results, retest in a couple of days or talk to your doctor about a follow-up blood test for confirmation. Following the directions on your pregnancy test helps avoid the confusion or disappointment of a false positive.
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No matter what, taking a pregnancy test can be an emotional roller coaster. When it comes to getting a false positive pregnancy test result, the experience can be deeply upsetting, particularly for anyone who has had a difficult time getting pregnant or is actively hoping to get pregnant (or both). The hope that comes with seeing that positive sign crashing down as you realize it was a false positive pregnancy test? It's a uniquely devastating emotion.
Of course, getting a false positive pregnancy test when you’re actively trying not to get pregnant can be just as horrible. Yup, you could probably do without the panicked verification trip to the ob-gyn, just to learn there was nothing to stress over.
Thankfully, experts note that false positive pregnancy tests are rare. Unfortunately, though, they can happen. Here are some of the most common causes of a false positive pregnancy test, along with some additional information that can help you put it all into context.
What is a pregnancy test? | How pregnancy tests work | False positive pregnancy test causes | Next steps after a false positive pregnancy test
First, what is a pregnancy test?
Let's start with the absolute basics just to make sure we're all on the same page. A pregnancy test tells you if you’re pregnant or not. That's simple enough to understand. But it's understandable if you're a little fuzzy on the details of what these devices actually look for to identify a pregnancy.
At-home pregnancy tests check for the hormone hCG. HCG is short for human chorionic gonadotropin, which the body creates during pregnancy. Right after a fertilized egg attaches to the uterine lining, the placenta then forms and starts producing hCG1. A blood test can detect hCG about nine days after conception, and a urine test can detect it 12 to 14 days after conception, according to the Cleveland Clinic, although it varies—some especially sensitive urine tests can detect a pregnancy even earlier. A person’s hCG level typically doubles every 72 hours through 8 to 11 weeks of pregnancy. Then it remains consistent and starts to go down after delivery.
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How does a pregnancy test work?
An at-home pregnancy test is designed to find hCG in pee2. If the hormone is present, it triggers a chemical reaction and the test signals that you're pregnant. If hCG is not present, the test will say you aren't pregnant. Many tests use two lines to mean you’re pregnant and one line to mean you’re not—but it depends on the test brand. Some tests use plus and minus signs. Some digital pregnancy tests have a screen that plainly reads "pregnant" or "not pregnant." Which can save you some “Is that one line or two?!” squinting, at least.
Seems simple, right? As Ina Garten would say, "How easy is that?" Typically, pretty easy. Most at-home pregnancy tests claim to be about 99% accurate3. Ultrasounds typically can't detect a pregnancy until a little later in your pregnancy and that's why at-home tests are so useful. But, sometimes, other elements can mess with a pregnancy test's results and tell you you’re pregnant when you’re really not.
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What can cause a false positive pregnancy test?
Here are the most likely reasons you may end up with a false positive pregnancy test:
1. You let the test sit too long before looking.
If you take a standard pregnancy test with line indicators, it's important to check the results according to the specific instruction of the test. If you let it sit too long before reading the results, urine on the test can evaporate and make it look like you have two lines instead of just one. "Oftentimes people will see evaporation lines as urine starts to evaporate off the test," Jamil Abdur-Rahman, M.D., board-certified ob-gyn, tells SELF. That might cause the test to look like it has a faint second line—making it positive—but it really only has one.
The best way to avoid this: Read the pregnancy test's directions and follow them exactly. The popular pregnancy test brand First Response, for example, instructs users to wait three minutes after taking the test, then read it as soon as possible4.
2. The pregnancy test is expired.
The second most common reason Dr. Abdur-Rahman's patients get false positives is because the test is expired, he says. When a test is past its expiration date, the chemical that detects hCG doesn't always work as it should, and you’re more likely to get a misread. "The test can expire and the chance of having a false positive increases," Dr. Abdur-Rahman says.
3. You’re on fertility medications that raise hCG levels.
If you take a pregnancy test too soon after taking a fertility drug that contains hCG—like some injections that are often part of in vitro fertilization—you could get a false positive.
7 Reasons Your Pregnancy Test Gave A False-Positive
Pregnancy tests hold a lot of weight. With one positive test, your entire life will change. But what about when a test comes back falsely-positive? A false-positive test result only happens less than 1% of the time, but when it does, it can make the following days or weeks confusing before you realize you’re not actually pregnant.
So what actually causes a false-positive test and how do you decrease the chances of it happening to you? We’ll cover the top reasons for false-positive pregnancy tests below, but if you’d like to learn more about how tests work, click here.
False Pregnancy Test Results
In some cases, tests offer a false result. But, in other cases, they detect the presence of an embryo, even if the pregnancy is not viable. For the first five points below, we’ll cover false results where the test detects elevated hCG (the pregnancy hormone) and indicates a pregnancy that does not exist. The final two points, we’ll cover instances when the test accurately detects hCGs in a pregnancy that is not viable.
1. You Had A Miscarriage or Abortion Recently
After an embryo implants , it begins to secrete human chorionic gonadotropin (hCG), the pregnancy hormone. HCG is produced by the cells surrounding a growing embryo. The presence of hCG triggers a positive test result.
After an abortion or miscarriage, hCG levels start to go down over the a period of 9-35 days. If you take a pregnancy test within this window, you can get a false-positive result because the test is still detecting the pregnancy hormone and can’t tell that the levels are decreasing.
2. Some Medications Can Trigger False-Positives
If a woman is having a hard time getting pregnant, her doctor may put her on fertility treatments. Some of those medicines include hCG which helps follicles release mature eggs within a woman’s ovary. If a pregnancy test is taken within 7-14 days after fertility treatments, a false-positive can occur. It is recommended to delay pregnancy testing until 1-2 weeks after the last injection or treatment.
Tell your doctor if you’re taking any medication because various medicines can trigger false-positives. Once your physician knows what you’re taking, he or she can help you with over-the-counter test results.
3. Medical Conditions Are Sometimes to Blame
Sometimes medical conditions can trigger a false-positive in urine tests. If you have any of the following, they might inflate your hCG levels and you might get a false-positive:
* Ovarian cysts
* Kidney disease
* Urinary tract infection
* Pituitary problems
* And in some cases, ovarian cancer and other serious diseases
If you get a false-positive test result and have ruled out other causes, consult a medical professional to test for these conditions. Your doctor may recommend a blood test to get a more accurate test result.
4. Confusing Evaporation Lines
If the pregnancy test instructions were not followed precisely, sometimes an evaporation line can be mistaken for a positive. Many tests show two lines when hCG is detected and one line when hCG isn’t detected, or a plus or minus sign.
For the line tests, sometimes, a faint-colored second line appears. This may represent an early pregnancy or may simply be an evaporation line.
If you read the test after the recommended time in the instructions, the results might be a false-positive since the evaporation line may show up more clearly. Avoid any confusion by following the test’s timing directions exactly as they’re written. Each test brand has specific instructions, so follow them closely.
5. User Error
Like most consumer goods, pregnancy tests expire and are sometimes used wrong. Using a test incorrectly or using an old one can lead to a false-positive result. Here are a few tips to avoid user error:
* Before using your test, check the use-by date and follow the instructions closely.
* Use the tests when your urine is concentrated like when you wake up in the morning. Diluted urine from excessive water-drinking can affect the accuracy of the test.
* Avoid using a test too early in your menstrual cycle.
* Leave the dip-stick in your urine stream for the exact amount of time required by the instructions. Set a timer to keep track.
* Set another timer to check your results in the correct time frame outlined in the instructions.
Technically-Positive Pregnancy Test Results
The next two points are unique in that they indicate the presence of BhCG in the body so they are technically accurate in giving a positive result. However, an ectopic or chemical pregnancy sadly is not viable.
6. An Ectopic Pregnancy
When an embryo implants itself outside the uterus , it’s known as an ectopic pregnancy. Almost all ectopic pregnancies—more than 90%—happen in a fallopian tube. As the pregnancy grows, it can cause the tube to burst (rupture). A rupture can cause major internal bleeding. This can be a life-threatening emergency that needs surgery.
Even though the embryo isn’t viable it will still produce hCG, triggering a positive pregnancy test.
If you think you have an ectopic pregnancy, or have a positive pregnancy test paired with severe pain on one side of the lower abdomen and spotting, seek immediate medical help as soon as possible.
7. A Chemical Pregnancy
A chemical pregnancy is a miscarriage that happens before week five of the pregnancy when an embryo implants in your uterus but it never takes hold. The loss happens so early that you may not even know you're pregnant. However, the embryo produces hCG and can cause a false-positive on a pregnancy test. This situation is known as a chemical pregnancy.
Chemical pregnancies aren’t a result of action or inaction by the woman but can occur because of:
* Scar tissue
* Low amounts of certain hormones like progesterone
* An irregular-shaped uterus
The emotional strain from false-positive results can be severe and mentally taxing for you and your family. We recommend waiting to use at-home pregnancy tests until one week after the expected start of your period.
We also recommend getting a confirmed diagnosis at a local clinic or with your healthcare provider. You can always book a 30-minute appointment for a free pregnancy test at The Source clinic nearest you. Click the button below to schedule a free appointment today.
Davina is a native of Grenada and a graduate of The University of Texas at Austin. She's a content specialist with a passion for empowering women to thrive and reach their full potential. In her free time, Davina is probably painting, reading, or baking something unnecessarily sweet.
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