American teens who pledge to remain virgins until marriage have the same rates of sexually transmitted diseases as those who don't pledge abstinence, according to a study that examined the sex lives of 12,000 adolescents.

Those who make a public pledge to abstain until marriage delay sex, have fewer sex partners and get married earlier, according to the data, gathered from adolescents aged 12 to 18 who were questioned again six years later. But the two groups' STD rates were statistically similar.

The problem, the study found, is that those virginity "pledgers" are much less likely to use condoms.

"It's difficult to simultaneously prepare for sex and say you're not going to have sex," said Peter Bearman, of Columbia University's department of sociology, who co-authored the study with Hannah Bruckner of Yale University.