Association of prenatal perchlorate, thiocyanate, and nitrate exposure with neonatal size and gestational age

•We related maternal urinary NIS inhibitor levels to fetal growth measurements.•Prenatal exposure to NIS inhibitors was not associated with fetal weight or length.•Maternal perchlorate levels were associated with smaller fetal head circumference.•Other NIS inhibitors were associated with greater head circumference.•Prenatal exposure to these anions may have developmental effects beyond fetal size. Perchlorate and similar anions compete with iodine for uptake into the thyroid by the sodium iodide symporter (NIS). This may restrict fetal growth via impaired thyroid hormone production. We collected urine samples from 107 pregnant women and used linear regression to estimate differences in newborn size and gestational age associated with increases in perchlorate, thiocyanate, nitrate, and perchlorate equivalence concentrations (PEC; measure of total NIS inhibitor exposure). NIS inhibitor concentrations were not associated with newborn weight, length, or gestational age. Each 2.62ng/μg creatinine increase in perchlorate was associated with smaller head circumference (0.32cm; 95% CI: −0.66, 0.01), but each 3.38ng/μg increase in PEC was associated with larger head circumference (0.48cm; −0.01, 0.97). These anions may have effects on fetal development (e.g. neurocognitive) that are not reflected in gross measures. Future research should focus on other abnormalities in neonates exposed to NIS inhibitors.