Is having your period while pregnant hereditary?

My mom had her period until she was 5 months pregnant with me. Her period stopped with her first child, I am her second. The urine and blood tests kept coming back negative. In fact, she had to let the doctors know she was pregnant! I just got another period and just had one two weeks ago. Between that time I could have gotten preggo. I got off the IUD three months ago and my period HAVE BEEN regular until now. I was just wondering could this be hereditary? AND I am not one of those young teens that shouldn't be having so PLEASE don't talk to me that way. I am VERY grown and have 1 child already. Thanks.