A common false positive pregnancy test scenario goes like this. You have taken a pregnancy test and it says that you are pregnant. Soon, your period comes and you realize you are not pregnant. Why did the test say you were?
All pregnancy tests test for a pregnancy hormone call hCG or human chorionic gonadotropin. This hormone is released after the egg is fertilized and is implanted in the uterus (can take up to 12 days after fertilization to be implanted.) When this happens, hCG is released by the embryo and in a few days makes its way into your urine. hCG is important to your pregnancy because it helps other body parts (specifically the corpus luteum) function properly which is critical for pregnancy in humans.
When a pregnancy test tests your urine to see if you are pregnant it is only looking for this hormone that is in your urine, because this hormone is specifically made during pregnancy. However, there are statistics that say up to half of pregnancies are lost very early on. These miscarriages are commonly called “chemical pregnancies”. In most cases of “chemical pregnancies” the woman does conceive, and the embryo is implanted for a very short time before dying. During the miscarriage, the woman might bleed a few days after her expected period, and it may look like she has had her period, just like any other month. This is the reason for a false positive pregnancy test.
There are also cases of bleeding and still be pregnant, although this spotting is usually very light. The reason for this bleeding is because of the implantation process and the embryo attaching to your uterus. I hope this entry answered why a false positive pregnancy sometimes occur. Again, a visit to your doctor might help set your mind at ease! That is what they are there for!