There are theories that when woman cum during the male ejaculation, it helps the uterus contract and “suck up” the semen and sperm. On first thought it makes sense, but when you look at the anatomy of the Uterus and Vagina, the Uterus neck (Cervix) is actually about 90 degrees rotated off the top of the vagina, so if, say, it’s missionary style, the vagina would be lying horizontal and the Cervix and uterus would be vertical, on the top of the deep end of the vagina. But the pool of semen would be lying on the bottom of the deep end of the vagina when you shoot inside, so the uterus contraction during female orgasm wouldn’t actually be “sucking” on the pool of sperm and semen. Btw, thats why it hurts the girl when you are too long, coz you are slamming against the deep end of her vagina, which is a “dead end” with no opening lol.
Maybe during doggy style, the sperm will be in contact with the cervix more, and the sucking action will help. Either way, the sperm still needs to swim through the rest of the female reproductive system to reach the egg and inpregnat it at the fallopian tube.
So far, it seems there is no concrete scientific evidence to show that female orgasm will directly enhance chance of pregnancy on a physical per-cumshot basis. But girls are so sexy and a huge turnon when they orgasm, it makes you wanna fuck them many more times, which in the end can increase chances I guess!! Lol.