Thyroid function and perchlorate in drinking water: an evaluation among California newborns, 1998.

Perchlorate (ClO4-) has been detected in groundwater sources in numerous communities in California and other parts of the United States, raising concerns about potential impacts on health. For California communities where ClO4- was tested in 1997 and 1998, we evaluated the prevalence of primary congenital hypothyroidism (PCH) and high thyroid-stimulating hormone (TSH) levels among the 342,257 California newborns screened in 1998. We compared thyroid function results among newborns from 24 communities with average ClO4- concentrations in drinking water>5 microg/L (n=50,326) to newborns from 287 communities with average concentrations5 microg/L were observed, with 20.4 expected [adjusted prevalence odds ratio (POR)=0.71; 95% confidence interval (CI), 0.40-1.19]. Although only 36% of all California newborns were screened before 24 hr of age in 1998, nearly 80% of newborns with high TSH were screened before 24 hr of age. Because of the physiologic postnatal surge of TSH, the results for newborns screened before 24 hr were uninformative for assessing an environmental impact. For newborns screened>or=24 hr, the adjusted POR for high TSH was 0.73 (95% CI, 0.40-1.23). All adjusted odds ratios (ORs) were controlled for sex, ethnicity, birth weight, and multiple birth status. Using an assessment of ClO4- in drinking water based on available data, we did not observe an association between estimated average ClO4- concentrations>5 microg/L in drinking water supplies and the prevalence of clinically diagnosed PCH or high TSH concentrations.

Primary congenital hypothyroidism, newborn thyroid function, and environmental perchlorate exposure among residents of a Southern California community.

The objectives of this study were to evaluate whether there were higher rates of primary congenital hypothyroidism (PCH) or elevated concentrations of thyroid-stimulating hormone (TSH) in a community where perchlorate was detected in groundwater wells. The adjusted PCH prevalence ratio and 95% confidence interval (CI) comparing the study community to San Bernardino and Riverside counties combined was 0.45 (95% CI=0.06-1.64). The odds ratios for elevated TSH concentration were 1.24 (95% CI=0.89-1.68) among all newborns screened and 0.69 (95% CI=0.27-1.45) for newborns whose age at screening was 18 hours or greater. Age of the newborn at time of screening was the most important predictor of the TSH level. These findings suggest that residence in a community with potential perchlorate exposure has not impacted PCH rates or newborn thyroid function.