Your menstrual period bleeding and menstruation is falsely believed to be a "safe" period of time in your monthly cycle when you can have unprotected intercourse and not get pregnant. This is a myth, and nothing is further from the truth.
The simple answer is that it is possible to get pregnant from having sex while you have your period.
Sperm have the amazing ability to live for up to 5 days inside of the female body, which is why you can get pregnant during your period. This amazing survival time means that you can actually get pregnant — that the egg gets fertilized — on a different day than when you had sexual intercourse. That sounds strange, but it is true!
Some women can ovulate within 5 days of their menstrual period bleeding and get pregnant from having intercourse during the menstrual bleeding. And if you make love within 5 days of ovulation, then it is possible to get pregnant.
Can you get your period once you are pregnant?
It is possible but highly unlikely to have a regular menstrual period once you are pregnant. When you're pregnant, you may have some spotting or bleeding, but it's rarely a regular menstrual period. A regular menstrual period is moderate to heavy bleeding, lasting 3-5 days. Up to 30% of pregnant women experience some small amount of spotting or vaginal bleeding early in pregnancy (and most go on to have a normal pregnancy).
Some even report intermittent bleeding that seems like a regular period to them. But vaginal bleeding during pregnancy is not the same thing as menstruation.
What's the difference?
Menstruation only happens when you're not pregnant in response to ovulation and the uterine lining shedding when the egg has not implanted: Each month, your uterus grows a thick blood-rich lining in preparation for an egg to embed there. If you don't get pregnant that month, you shed this tissue and blood — that's your menstrual period. But once an egg embeds in the uterine lining, hormones tell the blood-rich tissue to stay intact to support the fetus.
If you are on the birth control pill or a vaginal hormone ring that is removed during menstruation, you are still covered while on your menstrual period. The hormones do not leave your body in that period of time, as long as you use your method as directed.