Repeat adolescent pregnancy and low birth weight: methods issues.

Longitudinal studies of the relationship between birth order and birth weight suggest that mean birth weight increases with parity among women of all ages. In contrast, national birth statistics and other cross-sectional studies of these relationships suggests a decrease in mean birth weight and an increased incidence of low-weight births with parity among adolescent mothers. We examine the potential reasons for these strikingly different conclusions. Our aim is to determine whether multiparity itself is a low-birth-weight risk factor among adolescent mothers or whether it is a marker for other adolescent maternal conditions that increase the risk of a low birth weight, independent of parity.