When your baby is ready to come, it's ready to come. And as we've seen on 'I Didn't Know I Was Pregnant,' it is sometimes a surprise to the expectant mother as well. In Sarah Michelle Gellar's case, as she detailed on 'Chelsea Lately' (Weeknights, 11PM ET on E!), her surprise came during a pilates class.

"I thought I was just really uncomfortable, but it turns out I was having a baby," she said.

Even afterward, she didn't believe she was really in labor when she went to the hospital. As it turns out, she was already in the process of delivering the baby.

"They said if you have another baby you better sit on the hospital steps at eight months and cross your legs," she said. Of course, we're not surprised that Buffy Summers slays at giving birth.