We know that rape is less likely to result in conception than consensual sex, if for no other reason than that people who engage in consensual sex are more likely to actually be trying to concieve, and therefore are targetting for the woman's ovulation time, whereas rape is more or less "random" and therefore the chance of it occurring during a woman's ovulation cycle is smaller.
During the monthly ovulation cycle, the egg has a life span of only 2-3 days for fertilization possibilities and the sperm in vagina can only live 2-4 days. So there are only a few days during the monthly cycle when conception can occur.
But that changes nothing how the sperm was introduced...by a loving husband or by force by a rapist. Both incidents have equal chance of conception. Conception has better chance with willing partners simply because they engage in sex more than once during the cycle, as opposed to only once by a rapist.
Todd Akin’s comments are offensive because when he says legitimate rapes has little chance of conception is that implies rape is no big deal, conception is unlikely and therefore abortion is a non-issue in a rape situation. My guess is 90% of women are seriously offended. It was easily the dumbest statement of 2012 by any politician.