Quote from Chandler in The Last One (Part One)
Doctor: I can't believe you didn't know it's twins. This has never happened before. Chandler: Well, gosh. That makes me feel so special and good. Monica: Wait, did you know it was twins? Doctor: Yeah, it's here in the paperwork we got from the clinic in Ohio. Monica: Anybody tell you? Erica: I don't think so. Although, they did mention something about two heartbeats. But I thought that was just mine and the baby's. They kept saying both heartbeats are really strong and I thought well, that's good 'cause I'm having a baby. Monica: This is unbelievable. Erica: Twins actually run in my family. Chandler: Interesting!