Can changes in sexual behaviors among high school students explain the decline in teen pregnancy rates in the 1990s?

Purpose: To explore the utility of using national data from high school students to explain changes in national declines in pregnancy rates. Although declines in teen pregnancy and birthrates in the 1990s have been welcome news to those interested in adolescent health and welfare, the reasons for these declines are not readily apparent. Previous attempts to explain these declines focused on the period before 1995 and did not directly calculate the impact of improved contraceptive use.

Methods: The national Youth Risk Behavior Survey provided estimates for sexual activity and contraceptive use among teens aged 15-17 years between 1991 and 2001 (n = 31,058). These data were combined with method-specific contraceptive failure rates (CFRs) derived from the 1988 and 1995 National Survey of Family Growth and pregnancy rates from the National Vital Statistics System. We calculated weighted-average CFRs (WACFR) and used the annual rate of change in the WACFR and sexual activity to estimate their relative contributions to the annual change in risk of pregnancy. Weighted least-squares regression in SUDAAN was used to test change over time.

Results: Between 1991 and 2001, annual rates of change in sexual behaviors were -1.7% for sexual experience and -1.6% for the WACFR. Improvements in WACFR resulted primarily from a decline in use of withdrawal (from 20% to 13%) and use of no method (from 17% to 13%) and an increase in condom use (40% to 51%). Recent sexual intercourse (i.e., intercourse during the past 3 months among teens who had ever had intercourse) did not change over time. The change in the estimated risk of pregnancy closely approximated the annual decline in the pregnancy rates for blacks and Hispanics but underestimated the actual decline for whites. Overall, 53% of the decline in pregnancy rates can be attributed to decreased sexual experience (95%CI 26% to 79%) and 47% to improved contraceptive use (95%CI 21% to 74%).

Conclusions: Use of school-based behavior data reflects well the pregnancy experience for school-age black and Hispanic adolescents, but does not track well with the pregnancy risk of white adolescents. Care should be taken in attributing changes in pregnancy rates to changes in behavior, given broad confidence intervals around these estimates. These data suggest that both delayed initiation of sexual intercourse and improved contraceptive practice contributed equally to declines in pregnancy rates among high school-aged teens during the 1990s; however, estimates varied among racial and ethnic groups.