So sayeth: http://www.pinke.biz/news/518/Lesbian-Teens-More-Likely-to-get-Pregnant-than-Straight-Teens/
The obvious problem here that I see is that they do not appear to have controlled for sexually active teens or not. The study itself may have, but this article does not mention it. I would not be surprised to find out (although I have no evidence one way or the other) that many GBLT folks start having sex earlier than their straight brethren.
Now, however, I feel that I may be stating assumptions not in evidence and falling for the classic "teh gheyz are horny" stereotype.