The percentage of U.S. teens having sex showed a "dramatic" drop between 1992 and 2002, while there was a similarly striking rise in the use of contraception by those who were sexually active, a new analysis of national U.S. data shows.

However, very recent increases in teen pregnancy — after a decline lasting more than a decade — show that more work needs to be done to help improve teens' reproductive health, according to Dr. Jennifer Manlove and colleagues from Child Trends in Washington, D.C.

"We need to continue to focus on this issue into the future to help reduce high rates of teen childbirth in the US, especially since things are trending in the opposite direction right now," Manlove told Reuters Health.

She and her colleagues looked at data from the 2002 National Survey of Family Growth for 1992, 1997 and 2002 to investigate the role of family environment, individual characteristics, and relationship types in teen sexual behavior. They report their findings in the Journal of Adolescent Health.

The positive trends Manlove and her team saw — for example, about 56 percent of girls and 61 percent of boys 15 to 19 years old had had sex in 1992, compared to 47 percent of girls and 46 percent of boys in 2002 — were directly linked to increasing levels of education among parents and a reduction in the percentage of teens who had been born to teen mothers, according to their analysis.

In 1992, 62 percent of girls and 65 percent of boys reported using contraceptives the first time they had sex, while that percentage rose to 72 percent for girls and 78 percent for boys in 2002.

Shifts in the nature of teen sexual relationships also were linked to these positive trends, including an increasing age at first sex.

Manlove and her colleagues found no evidence to back up media stories claiming that "hooking up" among teens is on the rise. "Based on these data we did not see any increases in casual sex," the researcher said.

It's not yet clear why the percentage of teen births has begun to climb again, Manlove said, although she agrees that massive coverage of celebrity teen moms like Bristol Palin and Jamie Lynn Spears could be one factor. "There has been a lot of media attention given to pregnant teens. You can't underestimate the power of the media."

Manlove said the evidence is clear as to what parents can do to help their teens delay having sex and avoid getting pregnant, or getting someone else pregnant. Having the "sex talk" is important, she commented, but overall good communication is also essential; even regular family activities like eating dinner together have also been shown to help teens put off sexual activity.

Parents should also talk with their children about what they expect from them, and encourage them to have goals and aspirations for the future, Manlove added. Studies have shown that adolescents who are looking forward to the future — for example, planning for college and anticipating a career — are less likely to have sex early and become teen parents, she said. "I think there's a lot parents can do."