Actually, I did a quick search for studies/scientific info on the subject of pregnancy from rape, I was astounded to find only two studies (hopefully there are more, locked up in the academic vault available for a price to fund the professors retirement). Most articles that bothered to quote any evidence cited one study...which if you've passed high school general science, is not conclusive evidence to prove anything more than you've conducted a study.
It is problematic to study pregnancies as a result of rape: first you have to have a definition of rape, then qualify cases that fit that definition. Where rape is alleged, did in fact a rape occur? How do we know?