Predictive relationship between adolescent oral and vaginal sex: results from a prospective, longitudinal study.

OBJECTIVES To (1) identify the temporal order between oral and vaginal sex onset; (2) test whether oral sex or vaginal sex is a risk or protective factor for the other; and (3) determine whether the relationship between oral and vaginal sex varies across time. DESIGN Prospective, longitudinal study with 6-month assessments conducted between 2002 and 2005. SETTING Self-administered surveys completed during class time. PARTICIPANTS At baseline, 627 ninth grade high school students from 2 northern California schools were included in the study. MAIN OUTCOME MEASURE Oral and vaginal sex onset. RESULTS Among sexually active adolescents, most initiated vaginal sex after or within the same 6-month period of oral sex initiation. Adolescents who initiated oral sex at the end of ninth grade had a 50% chance of initiating vaginal sex by the end of 11th grade. In comparison, adolescents who delayed until the end of 11th grade had a 16% chance of initiating vaginal sex by the end of 11th grade. CONCLUSIONS The first 2 years of high school may be a critical age period for adolescents' vulnerability to vaginal sex initiation via oral sex behaviors. Comprehensive evidenced-based interventions and provision of preventive services aimed toward reducing sexual risk should be expanded to include the role oral sex plays in adolescent sex behavior.