I had asked this question some time ago. The current premise is similar, but without the fantastical elements such as magic and demons. In this scenario, women have the innate birth control and the ability to control their reproductive functions. This ability developed early in human history and has helped lead to a matriarchal system developing. Pregnancy is an active process, and gestation rate can be controlled or pause to some limited extent. All drawbacks from pregnancy have been removed, such as morning sickness, cramps, etc. birth is a relatively painless process, which can be held off until the mother is ready in a convenient time.
The question is: would taking the randomness out of human reproduction by adding limit genetic diversity. If a natural form of birth control was present early in evolution, would it lead to homogeneity in the human species?