female, pregnancyIt is quite clear that a male ejaculation (often accompanied by an orgasm) is required to cause pregnancy as that is the source of the sperm which fertilizes the egg. It is also clear that a female orgasm is not required in causing pregnancy as well, but does a female orgasm have a significant effect on the chance of getting pregnant?
There are a few theories as to the purpose of the female orgasm. The only theory of which I am aware that involves pregnancy is the "upsuck theory" which is largely debunked.
In the early 1900’s, it was widely believed that the female orgasm was necessary for fertilization, according to the popular up suck theory. In the 1950’s William Masters and Virginia Johnson tested this hypothesis—which postulated that orgasmic contractions sucked semen into the uterus—by applying artificial semen mixed with a radio-opaque substance, which showed on an X-ray, to a cervical cap and had the women orgasm. They found no evidence of up suck.
Source: The Biology of the Orgasm.
Other resources appear to corroborate the assertion made in that article: while it sounds plausible, medical evidence shows that this theory is debunked. Furthermore, I have not been able to find any other notable claim that the female orgasm has a significant effect in starting pregnancy.
As Snowman said, there is no credible evidence that the female orgasm increases the chance of conception. There have also been several studies that have looked for correlations and have found none. E.g., "No direct relationship between human female orgasm rate and number of offspring," Animal Behaviour, Volume 86, Issue 2, August 2013, Pages 253–255, which studied over 8000 female twins and siblings and concluded that "It is unlikely that female orgasm functions to enhance fertility." (Sorry for the paywall.)
There's also a good evolutionary argument that it doesn't. Quite simply, anything that directly improves the chance of conception tends to be strongly selected, and the hit-or-miss nature of the female orgasm, and the very high numbers of women who seldom or never have orgasms during vaginal sex, would both argue that no such evolutionary advantage exists. If the female orgasm made a significant difference to conception rates, it would be at least as common and reliable as the male orgasm.
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