Before birth control, prostitutes must have been pregnant like 24/7, so what happened to all these enormous amounts of kids? Or did they use some other method than what we are using now? Or did they figure out abortions back then already?
The Hyppocratic Oath, written in 5th century BC, mentions some kind of medicine which kills the fetus. Although it bans its use by physicians, it means that ancient Greeks, at least, knew how to do abortions. There are some plants that act as natural abortifacients, one of them was silphium, extinct nowadays.
Also, there's an opinion based on some archaeological evidence, that the Roman prostitutes killed their infants just after birth. However, there are also arguments again this notion, one of them the aforementioned knowledge of abortifacients. You can read about this here:
http://archive.archaeology.org/9703/newsbriefs/ashkelon.html