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Thyroid hormone parameters during pregnancy in relation to urinary bisphenol A concentrations: A repeated measures
Max T Aung1, Lauren E Johns1, Kelly K Ferguson2
1Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, MI, United States.
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 35.1weeks 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.