Why did the pregnancy test show a positive, but I got my period anyway?
There are, essentially two reasons that a pregnancy test could show a positive, but you get your period anyway. The first is that the pregnancy test produced what is called a “false positive” result.
Home pregnancy tests are usually around 97% accurate when used correctly. However, there are several things that can cause a home pregnancy test to show a positive when you are not actually pregnant. They include:
Chemical pregnancy – this is, essentially, a very early miscarriage. Some studies have suggested that as many as half of all first pregnancies end in miscarriage, and this often happens in the first few weeks of pregnancy. In this situation, without a home pregnancy test, the mom-to-be would never have known she was pregnant to begin with.
Evaporation lines – Some pregnancy tests will leave a faint line of evaporation as the urine crosses the test. The line is most often gray in color and can sometimes be interpreted as a positive result. Certain brands of home pregnancy tests are known to very seldom leave evaporation lines.
Drug Interference – some medications have the pregnancy hormone hCG (Human Chorionic Gonadotropin). This is the hormone measured by a home pregnancy test. This is especially likely with certain medications used to treat infertility.
The other possibility is that you have not started your period, but are experiencing vaginal bleeding. Vaginal bleeding is relatively common in the first trimester, and occurs in about 10% of women. Some amount of vaginal bleeding may be normal; however, If you believe you are pregnant but have vaginal bleeding, it may be indicative of a larger problem and you should contact your physician.