Does the timing of sample collection confound the association between prenatal serum PFAS concentrations and birthweight: results from two prospective cohort studies.

BACKGROUND

Maternal serum concentrations of per- and polyfluoroalkyl substances (PFAS) during pregnancy have been consistently associated with reduced birthweight. However, these associations may be confounded by the timing of sample collection due to pregnancy-related changes in pharmacokinetics that impact both serum PFAS concentrations and birthweight.

METHODS

We measured nine serum PFAS concentrations in each trimester among 728 women in the MABC Study (Ma'anshan, China, enrolled 2013-2014). We estimated covariate-adjusted differences in birthweight for individual PFAS and their mixture, as well as percent change in PFAS by infant birthweight. We repeated our analyses in 70 women-infant dyads from the HOME Study (Cincinnati, Ohio, enrolled 2003-2006) with repeated PFAS measures in 2nd trimester and at delivery.

RESULTS

Associations of individual PFAS and their mixture with birthweight became more strongly inverse for measurements taken later in pregnancy. Each SD increase in log2-transformed 1st and 3rd trimester PFOA was associated with a 6-gram (95 % CI:-35, 22) and 26-gram (95 % CI:-54, 3) decrease in birthweight, respectively. Concentrations of six PFAS declined more steeply among women who gave birth to larger vs. smaller infants. PFOA declined by 11.3 % (95 % CI:-12.7, -9.9) vs. 8.9 % (95 % CI:-10.3, -7.5) per 13 weeks among women who gave birth to infants born at the 90th vs. 10th birthweight percentiles, respectively. We observed similar findings in the HOME Study.

CONCLUSIONS

These findings suggest that physiological changes in pregnancy may confound associations between serum PFAS and birthweight. Studies with PFAS measures later in pregnancy may overestimate the true effect of PFAS on fetal growth.