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Exposure to BPA affects maternal and neonatal thyroid function


A recent study has found that women exposed to bisphenol A (BPA) during pregnancy may experience changes in their own as well as their baby’s thyroid function.

Supported by grants from the US Environmental Protection Agency and the National Institute of Environmental Health Sciences, researchers examined the relationship between BPA exposure during pregnancy and both maternal and neonatal thyroid function. Women in the study, primarily with low education and income levels, were enrolled before 20 weeks’ gestation and included 476 predominantly Mexican-American women living in Salinas Valley, California.

During the study, women provided urine samples at around 12 and 26 weeks’ gestation as well as blood samples for measurement of free thyroxine (T4) total T4, and thyroid-stimulating hormone (TSH) at around 26 weeks’ gestation. Blood spots were collected from neonates at a median of 21 hours after birth.

BPA was detected in 82% of the maternal samples with median concentrations of 1.1 to 1.2 μg/g creatinine, lower than the 1.9 μg/g creatinine in the 2007-2008 National Health and Nutrition Examination Surveys. For every doubling in BPA concentration during the second half of pregnancy, results showed a reduction in total T4 of 0.13 µg/dL. Additionally, doubling in the average of 2 BPA concentrations during pregnancy was associated with a 9.9% reduction in thyroid-stimulating hormone levels in only male newborns.

When the 2 BPA measurements at 12 and 26 weeks were averaged, BPA exposure was not associated with maternal TSH levels. Yet when only the measurement obtained closest in time to the thyroid hormone measurement was used, a doubling in BPA concentration was associated with a significant reduction in total T4.

The researchers noted that the health implications of a possible decrease in maternal total T4—but not free T4–is unclear because bound thyroxine is not biologically active. In addition, the clinical consequences of lower-normal neonatal TSH is unknown. The findings, the researchers said, suggest a transient effect of BPA.

Additional funding for the study was provided from the University of California Institute for Mexico and the United States (UC MEXUS) and the University of California Berkeley Center for Latino Policy Research.

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