After 14 years of steady decline, the rate of teen births rose 3% last year, according to a federal study released Wednesday.
Health officials were uncertain why the number was increasing and whether it represented the beginning of a trend.
But Mary-Jane Wagle, president of Planned Parenthood Los Angeles, said she believed the increase was due to the failure of abstinence-only education programs, which can make teens less aware of contraceptive options.
"Every study shows that abstinence-only funding does not work to reduce teen pregnancy," said Wagle, who was not involved in the research. "What Planned Parenthood would have hoped for would be money spent instead on comprehensive sex- education programs."
Bill Albert, deputy director of the National Campaign to Prevent Teen and Unplanned Pregnancy, a nonprofit and nonpartisan research group in Washington, added that after years of declining teen birthrates, "perhaps complacency has become the enemy of progress here."
He doubted that the abstinence-only program was to blame, largely because studies have shown that its impact has been negligible. "It really has not moved the behavior needle one way or another," said Albert, who was not involved in the study.
The new numbers were compiled by the national Centers for Disease Control and Prevention using 2006 birth records covering 99.9% of the United States. They calculated about 435,000 births to girls between 15 and 19, or 41.9 births per 1,000 teenage girls.
The largest increase was among black teens, whose birthrate increased 5% to 63.7 births per 1,000 girls. The rate grew by 3% for whites to 26.6 births per 1,000, and 2% for Latinas to 83 births per 1,000.
Only Asian teens saw a decline, dropping about 2% to 16.7 births per 1,000.
The teen birthrate in California also saw a 1.6% increase in 2006 to 37.8 births per 1,000 teenage girls, according to state figures. Dr. Bonnie Sorensen of the California Department of Public Health said the state accepts no federal money for abstinence-only education.
The last national increase in teen birthrates started in the late 1980s and peaked in 1991, when there were 61.8 births per 1,000 teenage girls, the CDC data showed.
Researchers said the declines that followed were the result of intense educational campaigns that discussed a range of issues, including abstinence, contraception and the risks of sexually transmitted diseases. Abstinence-only programs became more prevalent starting in 1996 due to significant increases in federal funding, Albert said.
The teen birthrate hit an all-time low of 40.5 births per 1,000 teenage girls in 2005, the data show. The declines in the teen birthrate had slowed in the years before 2005, said Stephanie Ventura, chief of the Reproductive Statistics Branch at the CDC and a co-author of the report.
While the increase from 2005 to 2006 is worrisome, the rate is still dramatically lower than the middle of the century, when women got married younger and had babies earlier in their lives, Ventura said. In 1957, for instance, there were about 96 births per 1,000 teenage girls.
"We shouldn't lose sight of the remarkable progress on an issue that traditionally was seen as a problem that couldn't be solved," said Claire Brindis, co-director of the Center for Reproductive Health Research and Policy at UC San Francisco, who was not involved in the study.
"The challenge is: We may have reached the first wave of young people . . . but each year there is a new group of teens," she said. "We need to regroup and recommit ourselves."
The CDC group also studied the birthrate for all unmarried women and found the rate has climbed about 20% since 2002. In 2006, there were 50.6 births per 1,000 unmarried women.
Women in their 20s, rather than teenagers, have been the main contributors to the increase, Ventura said. About 40% of these women are living with partners, so they do not appear to be single parents, she said.