Prenatal phthalate biomarker concentrations and performance on the Bayley Scales of Infant Development-II in a population of young urban children

Introduction: Evidence suggests prenatal phthalate exposures may have neurodevelopmental consequences. Our objective was to investigate prenatal exposure to phthalates and cognitive development in a cohort of young urban children. Materials and methods: We recruited pregnant women in New York City from 1998 to 2002 and measured concentrations of nine phthalate metabolites in urine collected in late pregnancy. We administered a neurodevelopmental screening instrument, the Bayley Scales of Infant Development II (BSID-II), to children who returned for follow-up at approximately 24 months (n=276). We estimated associations between phthalate metabolite concentrations in maternal urine and BSID-II indices (Mental Development Index (MDI), Psychomotor Development Index (PDI)). Results: We observed no associations between phthalate metabolite concentrations and performance on the MDI or PDI in boys and girls combined. We did, however, observe evidence of effect measure modification by sex. We observed several negative associations between metabolite concentrations and both MDI and PDI scores among girls, suggesting poorer performance across multiple metabolites, with estimates equal to a 2-3 point decrease in score per In-unit increase in creatinine-standardized metabolite concentration. Conversely, we observed multiple weakly positive associations among boys, equal to a 1-2 point increase in score per In-unit increase in metabolite concentration. The strongest associations were for the metabolites mono-n-butyl phthalate, mono-isobutyl phthalate, monobenzyl phthalate, and mono(3-carboxylpropyl) phthalate (MCPP). Conclusions: Girls of mothers with higher urinary concentrations of MCPP and metabolites of dibutyl phthalates had lower MDI scores on the BSID-II. These same biomarker concentrations were often associated with improved scores among boys. We observed similar results for MnBP, MCPP, and MBzP on the PDI. Given the prevalence of phthalate exposures in reproductive aged women, the implications of potential neurotoxicity warrant further investigation.