ATLANTA -- In a troubling reversal, the nation's teen birth rate rose for the first time in 15 years, surprising government health officials and reviving the bitter debate about abstinence-only sex education.

The birth rate had been dropping since its peak in 1991, although the decline had slowed in recent years. On Wednesday, government statisticians said it rose 3 percent from 2005 to 2006.

The reason for the increase is not clear, and federal health officials said it might be a one-year statistical blip, not the beginning of a new upward trend.

However, some experts said they have been expecting a jump. They blamed it on increased federal funding for abstinence-only health education that doesn't teach teens how to use condoms and other contraception.

Some key sexually transmitted disease rates have been rising, including syphilis, gonorrhea and chlamydia. The rising teen pregnancy rate is part of the same phenomenon, said Dr. Carol Hogue, an Emory University professor of maternal and child health.

"It's not rocket science," she said.

At the same time, some research suggests teens are using condoms far more often than they did 15 years ago.

The new teen birth numbers are based on the 15 to 19 age group of women, which accounted for most of the 440,000 births to teens in 2006. The rate rose to nearly 42 births per 1,000 in that group, up from 40.5 in 2005. That translates to an extra 20,000 births to teen mothers.

In 1991, the peak year for teen births, there were nearly 62 births per 1,000.

The new report is based on a review of more than 99 percent of the birth certificates from last year by the U.S. Centers for Disease Control and Prevention.