How effective is anal sex against pregnancy?

I have read on many websites that pregnancy, though unlikely, is still possible if semen dripped from the anus to the vaginal area, but I cannot seem to find any actual percentages of how often pregnancy occurs among women who have anal sex as a form of birth control. Please list your sources so that I can read up on this. Thanks!|||very low chances...just be careful you don't get sperm near the vagina...and also, urinary tract infections are very common with anal sex because there is bacteria in the intestinal tract and if it gets near the vagina/urethra it will cause a urinary tract infection, so NEVER go directly from anal to vaginal sex without cleaning up first...|||You don't need a percentage. What you've read is perfectly legit. If you have anal sex, pregnancy won't occur. If semen gets in her vagina, however, that's the only way she can get pregnant. Like the last guy said, that's why they make condoms, so that things like that don't happen.|||very effective.|||Well....it doesn't get you pregnant. But this is why we have condoms and birth control pills|||Wow I'm sorry, but the answers before me are just terrible. You have very near the same chance of pregnancy with anal sex. This is because the anus and vagina are in such close proximity to one another. Often when a male pulls out from anal sex this will bring semen out and only and inch or two at the most away from the vaginal opening. All I can say is that anal sex is usually not as enjoyable for the man or woman, so it's much better to have sex using proper birth control than having anal sex.