For those who don't want to read the rest of this column, the answer is: NO,
you can't get pregnant from anal sex.
What you have to understand is that the urogenital system is completely separated
from the gastrointestinal one. You can't get pregnant from anal sex for the same
reason you can't get pregnant from oral sex: the two tracts are entirely
unrelated, even if they are close to each other.
I know many have written me about unusual situations, so let's walk through a
worst case scenario. First, the man would have to ejaculate (and he should be
wearing a condom anyway, so this shouldn't be an issue). Next, the semen would
need to dribble out of the anus. The semen would need to contain a sufficient
number of sperm that were still viable (and not destroyed by time or the
inhospitable environment of the rectum). Those sperm would then have to
somehow migrate into the vagina. Sperm are not like flopping fish; they need
the environment of semen to survive. So, the semen -- with sperm intact --
would need to dribble into the vagina. Even if all this occurred (highly
unlikely), the sperm would then need to work their way up to the fallopian
tubes and hope to meet an egg at just the right time.
So, while I am not saying it is impossible I think you should spend
your time worrying about far more likely things that could happen, like a
giant cow crashing through your ceiling :)
