Fascinating! I'd only ever heard of one kind of prostaglandin and I didn't know there were others. The article doesn't mention this function of prostaglandins, but they help the cervix ripen in late pregnancy. They're found in semen--hence the advice that having sex will help you baby come faster--and doctors can also prescribe a gel with prostaglandins. They're often used if labor needs to be induced, but the cervix isn't soft and dilating yet.