Background: Pregnancy in adolescence is associated with an excess risk of poor outcomes, including low birth weight and prematurity. Whether this association simply reflects the deleterious sociodemographic environment of most pregnant teenagers or whether biologic immaturity is also causally implicated is not known.
Methods: To determine whether a young age confers an intrinsic risk of adverse outcomes of pregnancy, we performed stratified analyses of 134,088 white girls and women, 13 to 24 years old, in Utah who delivered singleton, first-born children between 1970 and 1990. Relative risk for subgroups of this study population was examined to eliminate the confounding influence of marital status, educational level, and the adequacy of prenatal care. The adjusted relative risk for the entire study group was calculated as the weighted average of the stratum-specific risks.
Results: Among white married mothers with educational levels appropriate for their ages who received adequate prenatal care, younger teenage mothers (13 to 17 years of age) had a significantly higher risk (P < 0.001) than mothers who were 20 to 24 years of age of delivering an infant who had low birth weight (relative risk, 1.7; 95 percent confidence interval, 1.5 to 2.0), who was delivered prematurely (relative risk, 1.9; 95 percent confidence interval, 1.7 to 2.1), or who was small for gestational age (relative risk, 1.3; 95 percent confidence interval, 1.2 to 1.4). Older teenage mothers (18 or 19 years of age) also had a significant increase in these risks. Even though sociodemographic variables associated with teenage pregnancy increase the risk of adverse outcomes, the relative risk remained significantly elevated for both younger and older teenage mothers after adjustment for marital status, level of education, and adequacy of prenatal care.
Conclusions: In a study of mothers 13 to 24 years old who had the characteristics of most white, middle-class Americans, a younger age conferred an increased risk of adverse pregnancy outcomes that was independent of important confounding sociodemographic factors.