Effects of prenatal exposure to five parabens on neonatal thyroid function and birth weight: Evidence from SMBCS study

Parabens, suspected as endocrine-disrupting chemicals, are nearly ubiquitous in the human body and exposure to these chemicals during pregnancy may disrupt thyroid hormones homeostasis and even affect fetal growth, although the impacts are still unclear. We aimed to estimate associations of maternal urinary paraben concentrations with cord serum thyroid hormones and birth weight. A subset of 437 mother-newborn pairs were included from a prospective birth cohort with five parabens quantified in maternal urine and seven thyroid function indicators measured in cord serum samples. Multivariable linear regression models and elastic net regression (ENR) models were applied to explore associations between individual and mixtures of prenatal urinary paraben concentrations and thyroid hormones and birth weight, respectively. Maternal urinary ethyl-paraben (EtP) concentrations were associated with increased cord serum total triiodothyronine levels (TT3) [percent change: 1.51%; 95% confidence interval (CI): 0.20%, 2.74%; p=0.017]. Urinary propyl-paraben (PrP) levels predicted higher thyroid peroxidase antibodies (percent change: 4.19%, 95%CI: 0.20%, 8.44%; p=0.041). Maternal urinary EtP and butyl-paraben (BuP) concentrations were significantly positively associated with birth weight [regression coefficient, (β)=40.9g, 95%CI: 3.99, 76.6; p=0.030; β=62.1g, 95%CI: 8.70, 115; p=0.023, for EtP and BuP, respectively]. In sex-stratified analyses, positive relationship between EtP levels and birth weight was observed in boys. Urinary EtP concentrations predicted higher TT3 levels in cord serum samples, assessing parabens as a chemical mixture with ENR models. Prenatal exposure to parabens may affect thyroid hormone indicators with increased serum TT3 levels and associate with higher birth weight, especially in boys. The underlying biological mechanisms and effects of prenatal paraben exposures on disruption of thyroid function homeostasis and potential impacts of childhood growth and development needed to be further investigated.