Is it possible to become pregnant by having sex the day your period starts?

Unlikely but . . .: Conception can from several days before to after ovulation which occurs 2wks prior to menses. So if your menses occurred, it's unlikely that you ovulated at the time of unprotected sex. With that said, some women do spot during implantation. So the best way to determine if you're pregnant (or not) is to take a home pregnancy test. If negative, go see your doctor for contraception (if desired).