Originally Posted by Shikra

I heard, and I forgot from whom but I think from my gynecologist friend, but the male sperm has prostaglandins (or something) in it that helps soften the cervix, which helps with the delivery. I believe that's what the doctors suggest the couple to have sexual intercourse when the girl has been in labor in a long time and sex at that time can help a bit more.

Edit: Found a reference online - How to induce labor