Contraception injection
From Memory Alpha, the free Star Trek reference.
The contraception injection was a form of birth control used in the Federation. The medicine had to be administered regularly, otherwise sexual intercourse could lead to fertilization and pregnancy.
In 2375, Benjamin Sisko, preoccupied by the latter stages of the Dominion War, forgot to renew his injection, despite repeated reminders from his CMO, Julian Bashir. As a result, his wife, Kasidy Yates, became pregnant with their child, the couple's first. (DS9: "The Dogs of War")
