Season 4, Episode 22 | March 26th, 2006
After a pregnancy scare, Peter reluctantly agrees to get a vasectomy to prevent further repeats. Before the surgery, he agrees to donate sperm, should Lois & he ever decide to have another baby. While in the sperm bank, Peter accidentally destroys all the existing samples, and decides to replace them with his own to prevent himself from getting in to trouble. Nine months later, a lesbian couple, who took away some of Peter's sperm in order to conceive a child. One of the lesbians gives birth to Bertram, Stewie's half-brother who first appeared in the episode "Emission Impossible."