Well, according to some politicians, woman have ways of preventing pregnancy by sheer willpower even now!
Mr. Laser Beam wrote:
Although in the ST III novelization, it is implied that birth control is a simple matter of will (David and Saavik are talking about it and David says something about "I passed all my exams in bio-control").
The first brings to mind Aeryn Sun from Farscape, the Sebacean women had the biological ability to not conceive and to "pause" (or reject) a pregnancy at it's earliest stages, and then months or years later deliberately continue the child's development at a more advantageous time.
The second sound like the Fremen in the novel Dune. Boys would taught in their teen years how have sex without ejaculating, an adult male who never learned the method would be unable to find a partner or wife, and to a minor degree be considered a danger to the group.