Can you have your period while pregnat?

It is very rare, but yes, you can have your period while pregnant. When you are pregnant, the lining of your uterus (womb) swells with new blood vessels and other tissue. This is what causes your period. However, sometimes the lining of your uterus can shed all or part of its lining even if you are pregnant. This is called a "decidual cast" and it can look exactly like a period, complete with cramps and bleeding. Usually, a decidual cast is just a little bit of tissue and blood, but it can be as heavy as a regular period. If you think you might be pregnant and you have bleeding or spotting, it is important to see your doctor to make sure that everything is okay.