The U.S. teen birth rate fell again in 2012, reaching a new historic low, according to a new report from the Centers for Disease Control and Prevention.

In 2012, the birth rate for teens ages 15 to 19 was 29.4 births per 1,000 teens — a 6 percent decline from the 2011 rate, and the lowest since the U.S. officially began tracking teen births in the 1940s.

Between 2011 and 2012, there were 305,420 births to teens ages 15 to 19, the fewest since World War II, the report said. [11 Big Fat Pregnancy Myths]

The U.S. teen birth rate has fallen nearly continuously over the last two decades, and has been in "historic low" territory for the last few years. The 2012 teen birth rate was less than half of the 1991 rate, when a spike in births occurred.

"The fact that the teen birth rate in the U.S. has been cut in half over the past 20 years is a stunning turn-around," said Bill Albert, chief program officer at the National Campaign to Prevent Teen and Unplanned Pregnancy, a nonprofit organization in Washington, D.C. "It is really remarkable progress," Albert said.

The drop is likely due to fewer teens having sex, and more teens using contraception, Albert said. Recent research suggest sexual activity among teens is on the decline. For instance, between 2006 and 2010, 57 percent of girls ages 15 to 19 said they had never had sex, an increase from 49 percent in 1995.

There are also more contraception options available to teens today, including highly effective IUDs, Albert said.

However, Albert said there is still work to be done to prevent teen pregnancy. "Despite this truly extraordinary progress, U.S. rates of teen childbearing remain far higher than in other countries," Albert said. The U.S. should not be "lulled into complacency by good news," he said.

The CDC report also found a drop between 2011 and 2012 in the birth rate for women in their early 20s, from 85.3 births to 83.1 births per 1,000 women, another record low.

The birth rate for women ages 30 to 34 increased slightly, from 96.5 births per 1,000 women in 2011 to 97.3 births per 1,000 women in 2012. Birth rates for women ages 35 to 39 also increased 2 percent from 2011 to 2012.

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Overall, the total number of U.S. births was about the same in 2012 as 2011, around 3.95 million. The fertility rate also held steady at 63 births per 1,000 women ages 15 to 44.

The rate of cesarean section deliveries remained unchanged, at 32.8 percent in 2012. The preterm birth rate fell for the sixth straight year, to 11.54 percent, down 2 percent from 2011, and down 10 percent since 2006.

The continuous reduction in preterm birth rates is "a trend in the right direction," said Dr. Diane Ashton, deputy medical director at the March of Dimes. "It means that there will be more babies born at term, and healthier," Ashton said.

One reason for the decline in the preterm birth rate may be a reduction in the rate of elective early deliveries, she said.

The report was released today (Sept. 6) by the CDC's National Center for Health Statistics.

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