Sibling Rivalry

S4, E22: After a pregnancy scare, Peter reluctantly agrees to get a vasectomy. However, after the operation, Peter's sex drive becomes non-existent, and when Lois packs on some extra pounds, Peter's interest is renewed and things heat back up in the bedroom. Meanwhile, Stewie's half-brother and rival Bertram confronts him, and they declare an all-out war for control over the playground.