I personally have never heard of miscarriage from sex. I know my bf & I had sex & he was a bit eager to get "it" in, I ended up having a bit of spotting since it had been over a week & my cervix is sensitive. So spotting is posdible after rough sex but I think, imo, that he wouldn't be able to pierce the cervix to get to the womb. If he cant get to the womb, I don't see how.he could harm the baby.