Almost 630 participants completed an initial sexual behavior questionnaire at the start of ninth grade, when they were 14 years old. Nearly 75 percent continued to respond to subsequent surveys every sixth months thereafter, up until the end of 11th grade.
Approximately 40 percent were white, 16 percent Latino, 22 percent Asian or Pacific Islander, 3 percent black, and 20 percent multi-ethnic or other ethnicity.
Of the initial survey group, about one-fifth had initiated oral sex and 71 students had had vaginal intercourse before the start of ninth grade.
But for all ages, oral sex was twice as likely to precede the initiation of intercourse rather than the other way around.
Teens who had engaged in oral sex by the end of ninth grade were at the highest risk of engaging in vaginal intercourse during high school, with a quarter going on to have intercourse by the end of ninth grade and half doing so by the end of 11th grade. Only about 9 percent of those teens abstained from vaginal intercourse through 11th grade. Most paired the two activities within the same six-month period.
By contrast, teens who delayed having oral sex until the end of 11th grade had a 57 percent change of avoiding vaginal intercourse through 11th grade. This could mean that teens who delay oral sex are more likely to delay vaginal sex as well, the authors said.
With the caveat that blacks were not well-represented, the authors said neither ethnicity, gender nor socio-economic background affected the results.
The authors said teens need to be better educated about the implications of oral sex.
"First, we simply need to talk to teens about sex more," Halpern-Felsher said. "And second, when we talk to teens we need to be more explici
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