Elsewhere on the site, James Hamblin applies some disinfectant to the notion that the female body can magically "shut that whole thing down":

In light of the pervasiveness of the abortion conversation, it's worth reviewing what we know about this aspect of reproductive physiology. 

From a holistic perspective, one might hypothesize that a woman's body could respond to the extreme stress and trauma of enduring rape in such a way that she would be physiologically more likely to miscarry (or not to conceive at all). There is a multi-million dollar alternative reproductive health market aimed at optimizing an environment for conception -- sexual positions, foods, colors, aromas, feng shui -- so there could be something to a theory that the other, much darker end of that spectrum functions analogously. 

But that doesn't hold, to any relevant degree. A widely-cited 1996 study from the American Journal of Obstetrics and Gynecology sampled over 4,000 women and found that the rape-related pregnancy rate was 5.0 percent. That is, after being raped once, a woman had a 5.0 percent chance of pregnancy. That number includes rapes in which condoms were used. Small studies from other countries have reported the percentage to be much greater.

RESULTS: The national rape-related pregnancy rate is 5.0% per rape among victims of reproductive age (aged 12 to 45); among adult women an estimated 32,101 pregnancies result from rape each year. Among 34 cases of rape-related pregnancy, the majority occurred among adolescents and resulted from assault by a known, often related perpetrator. Only 11.7% of these victims received immediate medical attention after the assault, and 47.1% received no medical attention related to the rape. A total 32.4% of these victims did not discover they were pregnant until they had already entered the second trimester; 32.2% opted to keep the infant whereas 50% underwent abortion and 5.9% placed the infant for adoption; an additional 11.8% had spontaneous abortion. 

CONCLUSIONS: Rape-related pregnancy occurs with significant frequency. It is a cause of many unwanted pregnancies and is closely linked with family and domestic violence. As we address the epidemic of unintended pregnancies in the United States, greater attention and effort should be aimed at preventing and identifying unwanted pregnancies that result from sexual victimization.