There was a recent update that modified the random npc's "behavior" that should result in less frequent pregnancies. For the more important, named npc's, the player can also gift things like pills to prevent or remove pregnancy, and pepper spray to prevent attacks. One or both changes may still be in the testing versions, but the dev is gearing up for a public release very soon.
Part of it is also due to the story of the game. If you missed it, birth control in the Fixer is outlawed and can only be obtained illegally in the black market.