Cumming In Me While I'm On My Period

Hey ladies so I just need some of you guys to tell me the likely hood of my getting pregnant from my bf cumming in me while I'm on my period. We do have sex when I'm on my period and we don't use protection ever, weather its that time of the month or not. And I'm not on bc but I want to know what the chances or if it's even possible for me to get pregnant from him cumming inside me while I'm on my period. He hasn't came in me while I'm on it before but if he does I just want to know what would happen..