Young American women between the ages 15 to 19 who got pregnant went up by 3.4 percent, according to the National Center for Health Statistics. It is the second straight year that teen birthrates rose in 2006 to 2007, reversing 14 consecutive years of declines.

In 2005 to 2006, teen birthrates grew 1.4 percent.

Stephanie Ventura of the NCHS said in a statement, "We may have reached a tipping point. It's hard to know where it's going to go from here."

The center said the reasons behind the rise are still not clear. Experts said the hike may have been caused by complacency toward AIDS and teen pregnancy.

The rise in pregnancies is not limited to teenagers, but also across all age groups from women in their 20s up to their 40s, and even older unmarried ones.

Ventura added that while teen pregnancy is going up, teen births among unmarried women now comprise only 23 percent versus 50 percent in the 1970s. "That shows the increases are driven by adult women 20 and older," she said.

With the report out, it will likely fuel debates over federal funding for sex education programs, particularly those that focus on pushing for abstinence till marriage, which gets $176 million annually in federal funds. Valerie Huber of the National Abstinence Education Association told Washington Post, "This is certainly not the time to remove any strategy that is going to provide skills for teens to avoid sex."

However, some groups want the program expanded to include teaching the youth about contraceptives because the U.S. could no longer afford to pay for abstinence only programs, said James Wagoner of Advocates for Youth.