Prenatal fluoride exposure and pregnancy outcomes in two US pregnancy cohorts.

BACKGROUND: Our goal was to evaluate the relationship between prenatal fluoride exposure and pregnancy outcomes. METHODS: We measured urinary fluoride collected during the second trimester among pregnant people recruited from California and Illinois from 2014 to 2020 (N = 949). We evaluated risk differences (RDs) of preterm birth (PTB), small-for-gestational age (SGA), large-for-gestational age (LGA), gestational diabetes, and differences in birthweight, birthweight-for-gestational age z-scores, and gestational age associated with a 0.1 mg/l increase in fluoride using linear regression to estimate effects on the additive scale. We also used modified treatment policies with machine learning to estimate the effects of hypothetical interventions to reduce urinary fluoride by 0.1 and 0.5 mg/l on pregnancy outcomes. In the Illinois cohort, we estimated effects by trimester. RESULTS: In our main analyses, we found no associations between urinary fluoride levels and pregnancy outcomes. For instance, for a 0.1 mg/l increase in fluoride, we saw no change in the risk of PTB, SGA, or gestational diabetes. We also found no differences associated with hypothetical reductions of prenatal fluoride by 0.1 mg/l or 0.5 mg/l for any outcomes. In the trimester-specific analyses for Illinois participants, we found increased LGA risk during the first (RD = 0.004, 95% CI -0.001, 0.009) and third trimesters (RD = 0.007, 95% CI 0.001, 0.012), and reduced LGA risk during the second trimester (RD = -0.006, 95% CI -0.011, 0.000), associated with 0.1 mg/l higher urinary fluoride. CONCLUSIONS: Prenatal fluoride exposure does not appear to affect pregnancy outcomes, but preliminary evidence suggests that higher fluoride levels may affect the risk of LGA depending on timing of exposure during pregnancy.