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.

If you take an at-home pregnancy test one morning to find a negative result, it may be too early to assume you're definitely not pregnant. Many such tests claim a certain percentage of accuracy several days before you've even missed your period, but the earlier you take it the higher the margin for error. Most doctors recommend that you wait until the first day after your missed period to take an at-home test, but ultimately the choice is yours.

Pregnancy tests display results based on the level of human chorionic gonadotropin hormone (hCG) detected in your urine. According to the American Pregnancy Association, "hCG is produced by the placenta shortly after the embryo attaches to the uterine lining and builds up rapidly in your body in the first few days of pregnancy." Because the hormone's levels multiply so quickly, it may be detected one day when it wasn't the day before.

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Because of that, the explanation for a negative test changing to positive overnight is pretty straightforward and simple. But what about a positive test changing to negative? Can that happen and if so, what does it mean?

Dr. Yvonne Bohn, an OB-GYN in Santa Monica, explains 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," Bohn says. "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.

In cases of chemical pregnancies, Bohn says the pregnancy test result will usually be a faint positive the first time but the follow-up tests will probably come out negative. Additionally, a woman will often know that the pregnancy is failing because of menstrual-like bleeding. The OB-GYN says that medical care is usually not necessary in such instances, as the bleeding should be like a heavy period and then end. If the woman experiences severe pain or heavier bleeding, Bohn advises she be seen by a physician.

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The miscarrying of a chemical pregnancy is not a woman's fault. Bohn explains that the pregnancy is not genetically normal so it simply does not continue to grow. Yet this can understandably be a emotionally distressing experience for a woman 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 alcohol or drug use, and controlling preexisting medical conditions effectively.

For many women, one at-home pregnancy test is not enough to confirm the growth of a healthy pregnancy (or to confirm that there is none). It is agreed to be best practice to take a second test a few days later, or to call your medical provider to get a blood test. At-home tests are an advancement certainly convenient for the modern woman, but we have to remember that they always need to be backed up.

Check out Romper's new video series, Bearing The Motherload, where disagreeing parents from different sides of an issue sit down with a mediator and talk about how to support (and not judge) each other’s parenting perspectives. New episodes air Mondays on Facebook.