HealthDay News — Maternal exposure to bisphenol A (BPA) during pregnancy affects both mother’s and baby’s thyroid function, research suggests.

Every doubling in urinary BPA concentrations during the second half of pregnancy was linked to a reduction in total thyroxine of 0.13 µg/dL, Jonathan Chevrier, PhD, of the University of California Berkeley School of Public Health, and colleagues reported online in Environmental Health Perspectives.

However, only the measurement taken closest in time to the thyroid hormone measurement correlated significantly with a reduction in total thyroxine. “Although we cannot rule out that average BPA concentrations during pregnancy may be relevant, the association of maternal BPA and total [thyroxine] was stronger when they were measured closer together relative to further apart in time, suggesting a transient effect of BPA.”

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Furthermore, the researchers found that every doubling in the average of two BPA concentrations during pregnancy resulted in a 9.9% reduction in thyroid-stimulating hormone (TSH) levels among male, but not female, newborns. The link was more robust when BPA was assessed in the third trimester, and was reduced with the time between BPA and thyroid hormone measurements in boys.

Prior results from the 2007-2008 National Health and Nutrition Examination Surveys (NHANES) indicated that 95% of U.S. women ages 18 to 44 had detectable BPA levels in their urine.

To further examine the relationship between BPA exposure during pregnancy, the researchers analyzed data from 476 predominantly Mexican-American women living in the Salinas Valley in California, who were participating in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) study.

Women were enrolled before 20 weeks of gestation, and provided urine samples for BPA testing at 12 weeks and 26 weeks gestation and blood samples for thyroid hormone testing at around 26 weeks gestation. The researchers collected neonatal blood spots at a median 21 hours after birth.

In this study, detectable BPA levels were identified in 82% of the maternal samples, and concentrations were lower than those observed in the NHANES study (1.1 to 1.2 versus 1.9 µg/g creatinine).

The results suggest a transient effect of BPA, which has a half-life of less than 6 hours in the human body, the researchers wrote. They added that the health implications of a possible decrease in maternal total thyroxine, but not free thyroxine, are unclear.

The researchers acknowledged the potential for residual confounding, and noted that the findings may not be generalizable beyond the mostly immigrant Mexican-American study cohort. Further studies are needed to better understand the relationship between prenatal exposure to BPA and thyroid hormone in pregnant women and children, they stated.


  1. Chevrier J et al. Environ Health Perspect. 2012; doi:10.1289/ehp.1205092.