The teenage birth rate declined 9 percent between 2009 and 2010, hitting an all-time low, according to new data released by the National Center for Health Statistics.

In 2010, there were about 34.3 births per 1,000 teenagers—or about one birth for every 29 teen girls—aged 15-19, a 44-percent decline from 1991 numbers and 64 percent lower than in 1957. Fewer babies were born to teenagers in 2010 than in any year since the peak of World War II. Laura Lindberg, of the Guttmacher Institute, which studies reproductive health, says better sex education and more widespread contraceptive use have contributed to the decline.

"It's always hard to draw conclusions from any individual year, but the use of hormonal [birth control] increased significantly," she says. Teenagers "doubling up" on birth control—using both a condom and hormonal birth control—may have also contributed to the decline.

Lindberg says the recent war on contraceptive use from conservatives in Congress and Republican presidential candidates threaten to roll back advancements.

"If we're going to stand up and applaud these declines in the teen birth rate as a positive social outcome, we need to provide teenagers and young adults with contraceptives," she says. "Any effort to roll back access to contraception for teenagers might result in a reversal of these numbers."

Between 2005 and 2007, there was a slight uptick in the teen birth rate. At the time, Stephanie Ventura, of the NCHS, told The Washington Post that the U.S. "may have reached a tipping point. It's hard to know where it's going to go from here." Since then, the birth rate has been in steady decline, reaching historic lows among all racial and ethnic groups.

Black and Hispanic teens are still having children at the greatest rate, but are quickly closing the gap between other groups. The number of black teens having children declined from 1-in-16 in 2007 to 1-in-20 in 2010, while the Hispanic birth rate declined from 1-in-13 to 1-in-18 over the same period. Just 1-in-100 Asian teens and 1-in-43 white teens gave birth in 2010.

On a state-by-state basis, there is a wide gap in the number of births—the south has many more births per 1,000 teen females than New England.

More than 1-in-20 teens had a child in Oklahoma, Texas, Arkansas, New Mexico and Mississippi. In Connecticut, Vermont, Massachusetts and New Hampshire, that number was less than 1-in-50. The birth rate is higher in typically more socially conservative states where it may be harder to obtain hormonal birth control, but Linberg says economics and educational attainment plays a role in those states as well.