Maternal low birth weight and adverse perinatal outcomes: the 1982 Pelotas Birth Cohort Study, Brazil.

OBJECTIVE To explore the association between maternal low birth weight (LBW) and adverse perinatal outcomes and to discriminate between confounders and mediating factors of these associations in a population-based birth cohort of Southern Brazil. METHODS Data from 794 female members of the 1982 Pelotas Birth Cohort Study known to have delivered a live-born singleton offspring up to December 2004 were analyzed. Maternal birth weights were recorded in 1982. The associations between maternal and offspring characteristics were estimated by Poisson regression. Confounding was tested for socioeconomic, demographic, and psychosocial factors. Maternal anthropometric characteristics and hypertensive diseases during pregnancy were considered mediating factors. RESULTS An increase of 100 grams (g) in mothers' birth weight predicted a gain of 21 g in their infants' birth weight (95% confidence interval (CI) 13.0-29.0 g, P < 0.001). Maternal LBW was associated with offspring LBW (prevalence ratio (PR) 2.28 (95% CI 1.34-3.89), P = 0.002), preterm birth (PR 1.78 (95% CI 1.12-2.81), P = 0.01), and small for gestational age (SGA) (PR 1.93 (95% CI 1.14-3.26), P = 0.01). A causal chain linking maternal LBW and offspring SGA was mediated by maternal prepregnancy weight. CONCLUSION Offspring of young women born with LBW are more likely to be LBW, preterm, and SGA. Public health strategies aimed at decreasing the frequency of LBW are necessary to reduce the perpetuation of adverse perinatal outcomes in later generations. The intermediate role of prepregnancy weight among LBW women opens a promising window to decreasing the prevalence of SGA in similar populations.