A long time ago I did a paper on teen pregnancy rates. One of the things I discovered was that in the 1950s teen pregnancy was huge. Just as huge as it was in the early '90s (which at the time was the most recent data). The rub? In the '50s those teen mothers were 19 and married instead of 16 and not.
I'm betting similar phenomenon is happening in the latest study of teen pregnancy rates in conservative and liberal areas Instapundit has brought up. In particular even if the age of the teenage moms is similar, the effect of abortion between the two is probably going to be very different.