Having sexual intercourse while menstruating could lead to pregnancy, because while the odds for pregnancy are lower on the days you are on your period, they aren’t zero, so it is unlikely but not impossible. Having sex during your period is not a 100% reliable way to prevent pregnancy.
Here are the reasons why you can get pregnant during your period;
First, some women may bleed when their ovaries release an egg each month, called ovulation, and this could easily be mistaken for a period. Since you are at your fertility peak when you are ovulating, if you have sex during this time, you stand a chance of getting pregnant.
Also, women who have a shorter cycle have a higher chance of getting pregnant if they have sex during their period. If your cycle is shorter, for example, every 21 to 24 days, this means you are ovulating earlier in the cycle. Sperm can live inside you for 2, 3 and up to 5 days. You could have sex towards the end of your bleeding and then actually conceive 4 or 5 days later with your early ovulation.
The probabilities of getting pregnant while on your period are low, but the possibilities are there, so if you are not sure of your cycle and do not want unplanned pregnancy, it is advisable to always use a condom or other form of birth control.