The Association of Maternal Age with Birthweight and Gestational Age: A Cross-Cohort Comparison

Background We examined the associations of maternal age with low birthweight (LBW) and preterm birth in four cohorts from a middle‐ and a high‐income country, where the patterning of maternal age by socio‐economic position (SEP) is likely to differ. Methods Population‐based birth cohort studies were carried out in the city of Pelotas, Brazil in 1982, 1993, and 2004, and in Avon, UK in 1991 [Avon Longitudinal Study of Parents and Children (ALSPAC)]. Adjustment for multiple indicators of SEP were applied. Results Low SEP was associated with younger age at childbearing in all cohorts, but the magnitudes of these associations were stronger in ALSPAC. Inverse associations of SEP with LBW and preterm birth were observed in all cohorts. U‐shaped associations were observed between maternal age and odds of LBW in all cohorts. After adjustment for SEP, increased odds of LBW for young mothers (