39. Declines in Pregnancies Among US Adolescents From 2007 to 2017: Behavioral Contributors to the Trend

Abstract

Pregnancies and births among adolescents in the United States have dramatically declined in recent decades. We aimed to estimate the contribution of three different proximal changes in behaviors to these declines among 14-18-year-olds over the period 2007-2017: delays in age at first sexual intercourse, declines in the frequency of sexual activity, and changes in contraceptive use, particularly the uptake of long-acting reversible contraception (LARC). We adopted an existing mathematical model that predicts number of sex acts per year per adolescent female by age, and the proportion of these that entail use of various types of contraception. We parameterized the model using predicted values from regressions based on six waves of the CDC’s Youth Risk Behavior Survey. We determined mean contraceptive failure rates from the literature. We calibrated our model to reported births using data from the National Vital Statistics System and the Guttmacher Institute. Pregnancy-related costs were calculated using both medical costs for all outcomes and costs to society for adolescent childbearing. Changes in the three behaviors (delays in age at first sexual intercourse, declines in subsequent frequency of sexual activity, and changes in contraceptive use) consistent with levels seen in our data resulted in reductions of 496,000, 78,000, and 56,000 pregnancies over the decade, respectively, with total medical and societal cost savings of $9.7 billion, $1.5 billion, and $1.1 billion. LARC adoption, particularly among 18-year-olds, explained much of the improvements from contraception use. The three measures together accounted for 38% of the observed decline in teen births over the decade. We conducted a sensitivity analysis on a fourth behavior—number of coital acts per partner—and found that a 50% reduction predicted births that closely matched observed data. Reported changes in sexual behavior among adolescents prevented an estimated 630,000 pregnancies and resulted in $12 billion cost savings over the decade. The LARC contribution was mainly seen among 18-year-olds. Comprehensive sex education should continue to build on existing strengths in terms of delaying age at first sexual intercourse, while further enhancing knowledge and access to contraception for all, and especially for those under 18.