Imagine millions of swimmers carrying sperm in search of an egg, making their way through the anus to the uterus in the hopes of fertilizing the egg but wait what! A dead-end! There’s no connection between the anus and the uterus and that’s anal sex for you.
One cannot get pregnant through anal sex. So a bigger concern must be the STIs which can very well be transmitted through it. So even though pregnancy is not possible, using a condom is still in your best interest.