If you didnt use protecion YES!!!!! What did you think theres Always a possibility when you dont use protection
If you are having sex when she has her period and you know for sure she was really having a period, the likelihood is that she will not get pregnant from that time. However, that said, there is always the odd time where it wasn't really a period just a little blood, or the "period" suddenly stops an hour later, or was just a light, unusual period with a late or early ovulation right near the period date, and if it is one of these things she would not be protected from pregnancy. In your position, I would use barrier birth control all the time, apparent periods or no.