Actually, I'd beg to differ; I do remember reading an article about this.

From what I remember, a lot of girls that get knocked up tend to be poor, unfortunate and most likely trafficked underage teenagers that didn't really know what they were doing or were forced into doing, rather than professional, adult prostitutes. Many hookers will often choose to always use contraception; after all a disease ridden or baby stretched vag can greatly damage future earning potential.