Subfecundity: a prenatal risk factor for adults but not for adolescents.

Young maternal age is associated with an increased incidence of low birth weight and prematurity; controlling for sociodemographic factors reduces the significance of this relationship. We hypothesized that this is partly because in a sociodemographically homogeneous population the adverse effects of maternal subfecundity on fetal growth confound the relationship between maternal age and infant outcome. To test this hypothesis, we studied the reproductive histories of 90 adolescent (less than 20 years old) and 35 adult lower socioeconomic, black prenatal patients. We found a strong, positive relationship between maternal age at conception and duration of unprotected intercourse prior to conception (r = 0.40; p less than 0.0001). Adults reporting 2 or more years of unprotected intercourse prior to conception were at highest risk for low birth weight (p = 0.02). Our findings demonstrate that it is important that adult controls for adolescent pregnancy studies have voluntarily postponed conception.