More U.S. Women Having Kids in Their 30s and 40s
Meanwhile, births among teens and women in early 20s fall to historic lows
"Last year there was some discussion that more teenagers are using birth control, and more were using more than one form of birth control," he said. "People were attributing that message getting out to teenagers as being important in this decrease."
Births among women in their 20s also continued to decline, a trend that has been occurring since 2008. The birth rate for women in their early 20s reached a new record low of about 83 births per 1,000 women.
McCabe chalked up the improvement in preterm births to the message getting out to women that they should have natural childbirth if possible and delay labor until it begins on its own.
"Certainly some women need to deliver early for their health and their baby's health, but otherwise they really should wait until 39 weeks," he said. "We now know that even in early term -- 37 and 38 weeks -- the outcome is very different than full term at 39 and 40 weeks. The mortality rate is higher."
The rate of births by cesarean section remained unchanged in 2012, however. A third of all births occurred via cesarean delivery.
"If you consider that the rate had been going up steadily prior to the last couple of years, then this is an improvement if you're looking for a decline in cesarean delivery," said report co-author Joyce Martin, a statistician at the CDC's National Center for Health Statistics.