Births are a recurring theme on Friends.
In "The One With The Sonogram At The End", Ross learns that his ex-wife, Carol, is pregnant with his child. Throughout the first season, Ross becomes involved and tries to help as much as possible like going to Lamaze class with her and her lover Susan. In "The One With The Birth", a baby boy whom they name Ben is born.
Frank Jr. Jr., Leslie, & Chandler Buffay
In "The One With Phoebe's Uterus", Phoebe's brother Frank Jr. and his new wife Alice ask Phoebe to be a surrogate mother and she agrees. Phoebe gives birth to Frank and Alice's triplets in "The One Hundredth".
The Season 8 finale deals with Rachel's birth to her and Ross' daughter, Emma. Emma's conception was unintended/accidental from a one-night stand, while Ross and Rachel weren't dating at the time and didn't want to be together.
Jack & Erica Bing
In part one of the series finale, Erica is rushed to the hospital to give birth to Monica and Chandler's child. After a baby boy is delivered, the doctor notifies them that "the next one will be on its way soon". Monica, Chandler, and Erica (and the rest of the gang) were unaware of this. However, Monica didn't care how many babies there were; She would keep them all. Then, Erica delivers a baby girl. They name them Jack (after Monica's father) and Erica (after her birth mother) respectively.