Can A Pregnancy Test Change Overnight? An OB-GYN Explains

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The time between when a woman suspects she might be pregnant and when it is confirmed for sure is the longest of her life. Regardless of whether you are hoping for a positive or a negative result, the odds are good that you are sweating bullets when the time to read the pregnancy test finally comes. And the wait isn't necessarily over upon seeing a result the first time; many women take the test several more times just to be certain. So what happens if you get a different result the next day? Can a pregnancy test change overnight? The answer is yes.

Not only can you get a negative pregnancy test result followed by a positive, but you can also get a positive test result and then a negative. If you take an at-home pregnancy test one morning to find a negative result, it could mean that you’re not pregnant, or it may be that you’re taking the test too early. But what about the reverse? Dr. Yvonne Bohn, an OB-GYN with Los Angeles Obstetricians and Gynecologists in Santa Monica, California, explains to Romper that this is likely a sign of a chemical pregnancy. "A chemical pregnancy is a very early pregnancy that usually ends about a week after the missed menstrual cycle," explains Dr. Bohn. "In a chemical pregnancy, the hormones of pregnancy are very low and the pregnancy doesn’t develop. The body recognizes and induces a very early miscarriage which is like a delayed menses.”

To wrap your head around this further, it’s helpful to know what pregnancy tests are even looking for. At-home pregnancy tests display results based on the level of human chorionic gonadotropin hormone (hCG), aka the pregnancy hormone, detected in your urine. If your numbers are elevated, the pregnancy test will show a positive result. If not, you’ll see a negative result. Most doctors recommend that you wait until after your missed period to take an at-home test, which can be difficult to do if you’ve been trying to conceive for some time. The reason why it helps to wait is because hCG increases throughout your first trimester, so the earlier you take the test, the higher the margin for error because you haven’t given your body enough time to hit the minimum amount of hCG needed to trigger a positive test result.

So the explanation for a negative test changing to positive overnight is pretty straightforward and simple. But what about a positive test changing to negative? What does it mean?

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In cases of chemical pregnancies, Dr. Bohn explains that the pregnancy test result will usually be a faint positive the first time but the follow-up tests will probably come out negative. Makes sense if the amount of the specific chemical the test is detecting in your urine drops when the pregnancy is not viable. Additionally, you will often know that the pregnancy is failing because of menstrual-like bleeding. She says that medical care is usually not necessary in such instances, as the bleeding should be like a heavy period and then end, but if you experience severe pain or heavier bleeding, you should be seen by a physician.

Let’s be clear: The miscarrying of a chemical pregnancy has nothing to do with what you did or didn’t do, and it is not your fault. Bohn explains that the pregnancy is not genetically normal so it simply does not continue to grow, and that’s why your body will induce a miscarriage on its own. Yet this can understandably be an emotionally distressing experience for any person to go through, especially if she was celebrating being pregnant only the day before. She also shares that the chance of miscarriage may be reduced by taking proactive measures if you are trying to conceive, such as taking prenatal vitamins or folic acid, avoiding high substance use, and controlling preexisting medical conditions effectively.

For many women, one at-home pregnancy test is not enough to confirm that they are pregnant (there’s a reason why test brands don’t advertise themselves as being 100% accurate, after all), let alone that the pregnancy is healthy and will be carried through. Sure, a subsequent pregnancy test (or more) a couple days later can confirm (or contradict) initial results, but the best way to get the most accurate reading is to call your medical provider to get a blood test, followed by an ultrasound. At-home tests are an advancement certainly convenient for the modern woman, but we have to remember that they should be backed up by a professional.

Experts: Dr. Yvonne Bohn, OB-GYN with Los Angeles Obstetricians and Gynecologists in Santa Monica, California

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