S4E12 · The One With the Embryos

Complete story — includes the ending

Rachel and Monica demand that Chandler and Joey get rid of their pet birds when the rooster starts to crow incessantly every morning before sunrise. The four of them also have an argument about who knows whom better, which results in Ross designing a trivia quiz with high stakes: if the men lose, they give up their pets, but if the women lose, they switch apartments with the men. The result comes down to a tie breaker, which the girls lose, thereby forcing them to move. Meanwhile, the embryos from Frank Jr. and Alice have been successfully implanted into Phoebe's uterus, leading to a tense wait that ultimately results in Phoebe’s pregnancy albeit much pressure from knowing that the chance of pregnancy is quite slim, and the couple has invested all their life savings for the IVF. In 2009, TV Guide ranked this episode number 21 on its list of the 100 Greatest Episodes.