It is not possible to have a period during pregnancy, but there are some things that will cause a woman to bleed during pregnancy. Implantation bleeding, decidual bleeding, and miscarriage are all things that could make a women believe she is having her period during pregnancy when in fact she is not. Most types of bleeding that occur during pregnancy, other than bleeding from miscarriage, are typically not a major concern and may not be any threat to the health of the mother or the fetus. Any period-like bleeding that does occur during pregnancy should be promptly reported to a doctor so the possibility of miscarriage can be either confirmed or ruled out.
The reason that it is not possible for a woman to have a period during pregnancy is because the body releases hormones that cause the menstrual period to stop. When a woman has her menstrual period, her uterine lining thickens and sheds. During pregnancy, this lining protects and helps to nourish the fetus rather than thickening and coming out in the form of a period. Some bleeding during the first trimester is fairly common, and it can occasionally be perceived as a period when it is not. This often causes many women to be unaware of their pregnancies until they are two or three months along.
Implantation bleeding, while typically light, is often perceived as a period during pregnancy. This bleeding is usually one of the first signs to alert a woman to the fact she is pregnant, but because it typically occurs right around the time a woman would expect her period to arrive, it is often mistaken for a menstrual period. Implantation bleeding is usually better described as spotting, and it is usually light pink or brownish in color. This bleeding normally occurs about a week after conception, and it is the result of the embryo implanting itself into the uterine wall. Implantation bleeding is normal and not dangerous in any way, but it could cause a woman to miscalculate her due date if she believed it was a period.
Decidual bleeding is another type of bleeding that often occurs during early pregnancy. This type of bleeding is typically the result of parts of the uterine lining shedding before fully attaching to the placenta. Not all women have decidual bleeding, but it almost always happens in the first trimester when it does occur. A woman who experiences decidual bleeding should visit her doctor, but in most cases it is not cause for concern.
Miscarriage is another cause of bleeding during pregnancy. If a woman does not know she is pregnant, she may believe that a miscarriage is actually her period at first. A woman who is aware of her pregnancy will likely be concerned that something is wrong because a miscarriage typically causes painful cramps along with the heavy bleeding. When a miscarriage occurs, it is most often during the first three months of pregnancy, although it can happen later as well. A woman who believes she may be having a miscarriage should immediately seek medical attention.