Getting pregnant on your period is very unlikely, but it’s not entirely impossible. If it’s really important to you to avoid pregnancy, don’t assume that you’re “safe” during your period, and if you do have intercourse while on your period, always use birth control.
To understand why it is possible for you to get pregnant on your period, you should understand how your menstrual cycle works. Once a month, around the middle of your menstrual cycle, a mature egg is released by one of your ovaries into the abdomen. From the abdomen, the egg reaches one of your fallopian tubes, where it can survive for about 24 hours and up to 48 hours.
The egg is basically hanging out, waiting to be fertilized. You can only get pregnant if during those 24-48 hours sperm are present in your fallopian tube. If there is no sperm, and the egg is not fertilized, your body has no need for it, and will shed it along with the uterine lining. This is the bleeding you experience every month on your period.
Chances are you won’t get pregnant on your period because by the time you start bleeding, the egg that was released during your last cycle can no longer be fertilized, and a new egg hasn’t yet been released.
However, if your menstrual cycles are very short – say, 21 days, your body could ovulate, or release a new egg, just a few days after you started your period. A typical scenario: you have intercourse while you’re still bleeding. The sperm that entered your body during intercourse survives 4 days in your body. The new egg is released 3 days after having intercourse, which means you still have viable sperm in your body that is now able to fertilize the new egg. As I said, it’s an unlikely scenario – but it’s possible.
Another reason why you should avoid relying on bleeding to pinpoint a “safe period” in your cycle is that you could be mistaking spotting between your periods, which typically occurs right at the time of ovulation – when you are the most fertile – as your period.
So, can you get pregnant on your period? The short answer is “yes,” which means that if avoiding pregnancy is a priority, you should always use birth control, regardless of the timing of intercourse.