Originally posted by
It is extreamly rare and there has to be a fisure between the rectal tubes and the vaginal canal. There have been reported cases of women who had a hole between the vaginal wall and the rectal wall and were able to concive through anal sex.
Yep, I was about to mention this. Sometimes women can have a congenital fistula and they do not even know it because it is relatively small and has not yet caused them any problems.
There are some documented instances of pregnancy via anal intercourse because the woman had a fistula. These cases may be (considerably) rare, but it can happen. I remember reading about a case describing a woman who had no outer genitalia (i.e., no vulva or vaginal opening), so she and her husband always had anal intercourse. Yet she was able to conceive and bear several children this way due to a fistula connecting her anal canal to her internal vaginal canal. Interestingly enough, the flow from her menstrual cycle had always found its way out anally since she had no vaginal opening. But women who have small fistulae and who have a normal vaginal opening usually don't know about the fistula because the menstrual flow exits via the vaginal opening.
Also, even in women without a fistula, any semen that makes it to the vulva (by dripping down from the anal canal to the vulva when she is on her stomach or in the doggie position) could conceivably (pun intended) travel through the vaginal canal, resulting in pregnancy. Of course, if you were actively trying to have a baby, this (ejaculating on the outer vulva) is not the means I'd recommend trying as it is not nearly as likely to result in pregnancy, but it can (and does) happen to some women who had avoided vaginal penetration, but had allowed their partner to ejaculate externally on the vulva after manual stimulation and dry humping (though I maintain that the guy would have to ejaculate directly onto the naked vulva, which has become very wet with natural lubrication for this to ever successful happen . . . and even then it is probably a long shot -- though not an impossibility).
Moral of the story: don't use anal intercourse as a means of birth control. Any time you engage in anal or vaginal sex, make sure you are protected, be it with condoms, birth control pills, or what-have-you. Or have oral sex and be careful not to get any semen transferred to the vulva via fingers, lips, tongues, etc.
I didn't vote. I would have, had there been an option stating, "Not likely, though far from impossible."