While many states have aggressively restricted access to abortion, most of those laws were adopted in the past two years and are not believed to have played a role in the decline.
In fact, it’s access to birth control that accounts for the numbers.
Some experts cite a government study released earlier this year suggesting that about 60 percent of teenage girls who have sex use the most effective kinds of contraception, including the pill and patch. That’s up from the mid-1990s, when fewer than half were using the best kinds.
Experts also pointed to the growing use of IUDs, or intrauterine devices, T-shaped plastic sperm-killers that a doctor inserts into the uterus. A study released earlier this year by the Guttmacher Institute, a nonprofit organization that does research on reproductive health, showed that IUD use among sexually active women on birth control rose from less than 3 percent in 2002 to more than 8 percent in 2009.