First Trimester Phthalate Exposure and Infant Birth Weight in the Infant Development and Environment Study.

Phthalate exposure is widespread among pregnant women but whether it is related to fetal growth and birth weight remains to be determined. We examined whether first trimester prenatal phthalate exposure was associated with birth weight in a pregnancy cohort study. We recruited first trimester pregnant women from 2010-2012 from four centers and analyzed mother/infant dyads who had complete urinary phthalate and birth record data (N = 753). We conducted multiple linear regression to examine if prenatal log specific gravity adjusted urinary phthalate exposure was related to birthweight in term and preterm (≤37 weeks) infants, stratified by sex. We observed a significant association between mono carboxy-isononyl phthalate (MCOP) exposure and increased birthweight in term males, 0.13 kg (95% CI 0.03, 0.23). In preterm infants, we observed a 0.49 kg (95% CI 0.09, 0.89) increase in birthweight in relation to a one log unit change in the sum of di-ethylhexyl phthalate (DEHP) metabolite concentrations in females (N = 33). In summary, we observed few associations between prenatal phthalate exposure and birthweight. Positive associations may be attributable to unresolved confounding in term infants and limited sample size in preterm infants.