Seems it can be used as a bargaining chip...the mother won't press so hard for charges if the rapist agrees not to seek parental rights.
From CNN:
Raped, pregnant and ordeal not overWhile a student in my final year of college, at age 21, I was raped. I have dissected that moment -- the horrifying moment that I became a "victim" -- from every possible angle. I have poked and prodded, examined and re-examined. Regrettably, I have even suspected myself in a desperate, ultimately futile attempt to understand how I became a victim.
...Eight years after my rape, I find myself on trial against ignorance again. Rep. Todd Akin's recent comments that "legitimate rape" rarely results in pregnancy not only flout scientific fact but, for me, cut deeper. Akin has de-legitimized my rape.
You see, nine months after my rape, I gave birth to a beautiful little girl. You could say she was conceived in rape; she was. But she is also so much more than her beginnings. I blissfully believed that after I finally had decided to give birth to and to raise my daughter, life would be all roses and endless days at the playground. I was wrong again.
It would not be long before I would learn firsthand that in the vast majority of states -- 31 -- men who father through rape are able to assert the same custody and visitation rights to their children that other fathers enjoy. When no law prohibits a rapist from exercising these rights, a woman may feel forced to bargain away her legal rights to a criminal trial in exchange for the rapist dropping the bid to have access to her child.
I was not aware of such laws, and my mind is reeling.