Maternal urinary fluoride during pregnancy and birth weight and length: Results from ELEMENT cohort study

Epidemiological studies assessing prenatal fluoride exposure and anthropometry at birth are scarce, inconsistent and with methodological limitations. The aim of this study was to evaluate associations between maternal urinary fluoride (MUF) at each trimester of pregnancy and birth weight and length in 536 mother-child pairs in the Early Life Exposures in Mexico to Environmental Toxicants (ELEMENT) cohort study. MUF (mg/L) was measured using microdiffusion/fluoride-specific electrode from at least one trimester of pregnancy. Non-linear associations were assessed through segmented regression models (MUF and birth weight Z-score) and we used linear regression models for MUF and birth length Z-score. Models were adjusted for potential confounders including urinary creatinine concentrations as a covariate. Non-creatinine adjusted MUF levels at each trimester of pregnancy were 0.81, 0.86, and 0.82 mg/L, mean concentrations for first, second and third trimester, respectively. For birth weight, we identified a MUF breakpoint at 0.99, 0.68 and 0.58 mg/L, for first, second and third trimester of pregnancy, respectively. In the first trimester, an increase of 1 mg/L in MUF concentrations ≥0.99 mg/L was associated with an increase in weight Z-score at birth (β = 0.79; 95% CI: 0.10, 1.48; p = 0.02). Second trimester MUF (≥0.68 mg/L) was marginally associated with birth weight decrease (β = -0.25; 95% CI: -0.55, 0.04; p = 0.09) and third trimester MUF (≥0.58 mg/L) was significantly associated with birth weight decrease (β = -0.33; 95% CI: -0.63, -0.03; p = 0.03). We observed a linear and significant association between MUF and Z-score of length at birth only for the first trimester of pregnancy (β = 0.55; 95% CI: 0.07, 1.04; p < 0.02). Prenatal fluoride exposure was associated with birthweight z-score with different susceptibility windows. Our findings reinforce the hypothesis that maternal fluoride exposure may affect birth anthropometry.