It is possible for women to get pregnant even if she is bleeding from her vagina.

Sometimes ovulation may occur before your period is over and sometimes it happens soon after. In both cases, if there are sperms in the vagina, it is possible that the egg released during ovulation is fertilised and you get pregnant.

Also, in some cases, women experience slight bleeding during ovulation. Though this bleeding may look like menstruation, it is not. It is commonly known as mid cycle bleeding or spotting. If you have unprotected sex during this time, it is possible that you might get pregnant.

Illustration of a silhouette of a pregnant woman - Menstrupedia
  1. Can a girl get pregnant if she has sex during her period?, http://kidshealth.org