Thyroid hormone parameters during pregnancy in relation to urinary bisphenol A concentrations: A repeated measures study

Abstract

Background Maternal supply of thyroid hormones during pregnancy serves a critical role in fetal development. Although animal and in vitro studies provide evidence for thyroid hormone disruption as a result of bisphenol A (BPA) exposure, there is still a lack of evidence in human studies, particularly in the context of pregnancy. Objectives We aimed to explore the associations between urinary BPA concentrations and plasma thyroid hormone parameters during gestation in pregnant women, and also investigated potential windows of vulnerability during gestation. Methods Our study population included 116 cases of preterm birth and 323 controls from a nested case-control study. We measured BPA in urine and thyroid hormone parameters in plasma samples collected at up to four study visits during pregnancy (median for each visit: 9.64, 17.9, 26.0, and 35.1 weeks gestation). We used linear mixed models for repeated measures analyses, and multivariate linear regression models stratified by study visit to explore potential windows of susceptibility. Results In our repeated measures analysis, BPA and thyrotropin (TSH) were inversely associated. An interquartile range (IQR) increase in BPA was associated with an 8.21% decrease in TSH (95% confidence interval [CI]: − 14.2, − 1.83), and a 4.79% increase in free T4 (95% CI: 0.82, 8.92). BPA and TSH were also inversely associated in our cross-sectional analyses at visits 3 and 4. Conclusions Our results suggest that TSH is inversely associated with urinary BPA in a consistent manner across pregnancy. Disruption of TSH levels during pregnancy can potentially impact child development and interfere with normal birth outcomes.