Teens who pledge to remain virgins until marriage are more likely to take chances with other kinds of sex that increase the risk of sexually transmitted diseases, a study of 12,000 adolescents suggests.

The report by Yale and Columbia University researchers could help explain their earlier findings that teens who pledged abstinence are just as likely to have STDs (search) as their peers.

The latest study, published in the April issue of the Journal of Adolescent Health, found that teens pledging virginity until marriage are more likely to have oral and anal sex than other teens who have not had intercourse. That behavior, however, "puts you at risk," said Hannah Brueckner, assistant professor of sociology at Yale and one of the study's authors.

Among virgins, boys who have pledged abstinence were four times more likely to have had anal sex, according to the study. Overall, pledgers were six times more likely to have oral sex than teens who have remained abstinent but not as part of a pledge.

The pledging group was also less likely to use condoms during their first sexual experience or get tested for STDs, the researchers found.

Data for the study was taken from the National Longitudinal Study of Adolescent Health (search). An in-school questionnaire was given to a nationally representative sample of students in grades 7-12 and followed up with a series of in-home interviews roughly one, two, and six years later. It was funded in part by the National Institute of Child Health and Human Development and the Centers for Disease Control and Prevention (search).

Leslee Unruh, president of the National Abstinence Clearinghouse in Sioux Falls, S.D., called the study "bogus," disputing that those involved had pledged true "abstinence."

"Kids who pledge abstinence are taught that any word that has 'sex' in it is considered a sexual activity," Unruh said. "Therefore oral sex is sex, and they are staying away."

Millions of teens have signed written pledges or verbally promised to abstain from sex, part of a church-led effort to discourage premarital sex and the spread of disease. President Bush has boosted funding for abstinence-only education in schools.

Critics say that education needs to be coupled with safe-sex education to be effective.

"If adolescents only had sex in monogamous, married relationships, by definition there would be no STDs," Brueckner said, echoing President Bush's remarks in last year's State of the Union address. "But the majority of adolescents don't live like that. They do have sex."

Last year, the same research team found that 88 percent of teens who pledge abstinence end up having sex before marriage, compared with 99 percent of teens who do not make a pledge.