Akin did not say that women cannot get pregnant from rape. What he said (paraphrased) is that in many cases (not all), the woman's body will either prevent conception from taking place, or a miscarriage will take place. That is a fact. When a person is threatened, adrenalin is produced for the fight or flight syndrome. Cortisol is also released into the bloodstream. Cortisol is the agent that will prevent conception, or cause miscarriage. Read the medical literature.
He did use an unfortunate phrase when he said "legitimate rape". I believe what he meant was actual forcible rape, not "OMG! I've been screwing a guy my parents don't like, now I'm pregnant. I was raped" rape, i..e. abortion to avoid responsibility for actions.