As Monica's biological clock ticks away like a time bomb, Carol goes into labour. When Ross and Susan can't stop bickering over who gets to help Carol more, Phoebe drags both of them into a closet to settle their differences - but all three end up getting locked in just as Carol's about to give birth to the baby. And Rachel flirts with an OB/GYN who has a love-hate relationship with women's private parts.
Sometimes with shows, they have a really good episode before the final episode.
This is what this is. The reason why this episode was not the final is because the writers were looking for a Rachel cliffhanger which they could not do on this episode.