The rate at which U.S. women are having babies continued to fall between 2008 and 2009, federal officials reported Tuesday, pushing the teen birthrate to a record low and prompting a debate about whether the drop was caused by the recession, an increased focus on encouraging abstinence, more adolescents using birth control or a combination of those factors.

The birthrate among U.S. girls ages 15 to 19 fell from 41.5 to 39.1 births per 1,000 teens - a 6 percent drop to the lowest rate in the nearly 70 years the federal government has been collecting reliable data, according to a preliminary analysis of the latest statistics.

"The decline in teen births is really quite amazing," said Brady E. Hamilton of the National Center for Health Statistics, who helped perform the analysis.

The decrease marked the second year in a row that the birthrate among teens fell, meaning it has dropped for 16 out of the past 18 years. The 8 percent two-year decline strengthens hopes that an alarming 5 percent increase over the preceding two years was a aberration.

"Just in time for the holidays, a steep decline in teen birth has been announced," said Sarah Brown of the Campaign to Prevent Teen and Unplanned Pregnancies. "We now are, thankfully, back on track."

The reason for the record low remains unclear, but some experts attributed it to the recession, noting that the overall fertility rate as well as the total number of births in the United States fell a second straight year in 2009 as well.

"I would not have guessed that teenagers would be most responsive to the economic downturn, but maybe we need to revise our stereotypes," said Samuel Preston, a professor of demography at the University of Pennsylvania.

Brown and others agreed:

"When money is very tight, all of us think harder about taking risks, expanding our families, taking on new responsibilities," Brown said. "Now, I know that teens may not be as savvy about money as those in their 20s and 30s - they probably don't stress over 401 (k)s like the rest of us - but many teens live with financially stressed adults, and they see neighbors and older friends losing jobs and even losing houses. So they, too, feel the squeeze and may be reacting to it by being more prudent. . . . Maybe part of tightening our belts includes keeping our zippers closed, too!"

That fits with research released in the spring by the Pew Research Center, which found that states hit hardest by the recession experienced the biggest drops in births.

"Our evidence definitely suggested there was a link between the economic circumstances and what was going on with fertility," said Gretchen Livingston, a Pew senior researcher. "I suspect that's what we're seeing with these lower numbers. This fits with the historical picture as well."

Others suggested that the intense concern about the 2005 to 2007 increases and the attention it generated--including Bristol Palin's campaign against teen pregnancy, MTV's "16 and Pregnant" series and Washington's birth control-vs-abstinence debate - may have gotten through to teens. Some data, for example, indicate that use of birth-control pills and other forms of contraception among teen girls is increasing.

"Although the data are preliminary, it looks like improved contraceptive use is again driving the decline in teen birthrates," said John Santelli of Columbia University's Mailman School of Public Health.

The general fertility rate fell from 68.6 births per 1,000 females ages 15 to 44 to 66.7 in 2009, and the total number of births fell from 4,247,694 to 4,131,019, That direction appears to be continuing into 2010, according to early statistics collected between January and June. The overall drop pushed the fertility rate to about 2.01, a 4 percent decrease from 2008.

That is the largest decline since 1973, and it put the total fertility rate below the level needed to sustain the size of the population for the second year after being above the replacement rate in 2006 and 2007 for the first time in 35 years.

The birthrate for women in their early 20s fell 7 percent, which is the largest decline for this age group since 1973, according to the report. The rates also fell for women in their late 20s and 30s, although it continued to increase for women in their early 40s.

The rise in teen pregnancies had triggered an intense debate about whether increased funding for sex-education programs that focus on encouraging abstinence may be playing a role. As a result, proponents of abstinence education welcomed the new data, saying they exonerated their approach.

"These trends show that the risk-avoidance message of abstinence has 'sticking power' for young people," said Valerie Huber of the National Abstinence Education Association. "This latest evidence shows that teen behaviors increasingly mirror the skills they are taught in a successful abstinence education program."

Huber and others noted that the Obama administration has significantly reduced funding for abstinence-focused programs.

"With a change in policy away from abstinence education, we may expect to see a reversal of the teen pregnancy birthrate in the years to come," said Jeanne Monahan of the Family Research Council.

But critics of abstinence programs, who argue that the approach does not work, attributed the drop to the recession.

"We certainly don't want recession to be the most effective form of birth control in the U.S.," said James Wagoner of Advocates for Youth. "We still need structural reforms in sex education, contraceptive access and pragmatic public policies to ensure a long-term decline in the teen birthrate - during good economic times as well as bad."

The Obama administration has launched a $110 million teen pregnancy prevention effort that will support a range of programs, including those that teach about the risks of specific sexual activities and the benefits of contraception and others that focus primarily on encouraging teens to delay sex.