What is the World State's way of controlling overpopulation in Aldous Huxley's Brave New World?
After the chaos of the Nine Year's War, people opted for a top-down, controlled society. To help achieve this, the World State carefully controls the population. First, all children are "decanted" in hatcheries using a cloning process. This allows exact calibration of births:
“Eighty-eight cubic metres of card-index,” said Mr. Foster with relish, as they entered.
“Containing all the relevant information,” added the Director.
“Brought up to date every morning.” “And co-ordinated every afternoon.”
“On the basis of which they make their calculations.”
“So many individuals, of such and such quality,” said Mr. Foster. “Distributed in such and such quantities.”
“The optimum Decanting Rate at any given moment.”
“Unforeseen wastages promptly made good.”
As we see, the World State adjusts births on a daily basis to achieve the "optimum Decanting Rate at any given moment."
Second, only as many as 30 percent of the women, at most, are allowed to be fertile. The rest are given male hormones that make them freemartins: this can lead sometimes to them growing beards, but otherwise they are normal, but non-fertile, women.
Finally, euthanasia is an accepted part of the social order. Nobody is allowed to get old or infirm. Children are conditioned early to the idea that euthanasia is normal and good by being taken on happy field trips to euthanasia centers where they are given many treats. In fact, the Savage's reaction to his mother Linda's death disrupts the conditioning of a group of children who happen to be visiting the euthanasia center at the moment.
We might mention too that people are conditioned to find the idea of biological motherhood or fatherhood obscene and disgusting, leaving everyone perfectly happy to let the state control the test-tube births.
Since there is no natural procreation allowed (children are conditioned early in life to think natural motherhood as repulsive) in "Brave New World," babies are produced in the Hatchery and Conditioning Centre. There a controlled number of Alphas, Betas, Deltas, Gammas, and Epislons are manufactured by the Bokanovsky's Process in which one fertilized egg produces from 8 to 96 "buds" that grow into identical human beings.
Another precaution against overpopulation is in the manufacture of freemartins, women who are rendered infertile by having hormones from a male twin mixed with them. Thus, only 30% women are physically capable of reproducing; even they are given drugs to keep them infertile. Even so, the reproductive act is presented as only a recreational activity; promiscuity is encouraged so that the act will have no meaning other than physical pleasure: "Everyone belongs to everyone."