Maternal age and the size of White, Black, Hispanic, and mixed infants

To clarify the interaction between maternal age and race in the prediction of infant size at birth.

Birth certificate data was used to study the relationship between maternal age, race/ethnicity, and the size of term, singleton infants born to 91,061 healthy, non-smoking, non-substance using, primigravidas.

Maternal race/ethnicity (Black race: OR: 1.95, 95% CI: 1.49-2.56; Hispanic ethnicity: OR: 1.38, 95% CI: 1.19-1.61) and the interaction term, maternal age x race/ethnicity (OR: 1.06, 95% CI: 1.01-1.11) predicted small-for-gestational age (SGA) birth. The strength of the association between Black race and SGA delivery increased and the strength of the association between Hispanic ethnicity and SGA delivery decreased with age (P < 0.001 for trend). Thus, Black and Hispanic teenagers were more likely to have SGA babies than White teenagers (1.7% and 1.6%, respectively compared to 1.2%; P = 0.003). However, Black women who postponed childbearing until their mid-twenties were more likely to have SGA babies than their Hispanic and White counterparts (2.6% compared to 1.2%, and 1.0%, respectively; P < 0.0001).

The findings suggest that acquired maternal characteristic(s) cause the reproductive health of Black primigravidas to deteriorate and Hispanic primigravidas to improve with age.