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Updated: Jun 6, 2026

Long-term Behavioral and Reproductive Consequences of Embryonic Exposure to Low-dose Toxicants
Published on: March 6, 2018
Perchlorate in drinking water during pregnancy and neonatal thyroid hormone levels in California
Craig Steinmaus1, Mark D Miller, Allan H Smith
1Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Oakland, CA, USA. craigs@berkeley.edu
Objective:
To evaluate associations between maternal drinking water perchlorate exposure during pregnancy and newborn thyroid hormone levels.
Methods:
Elevation in thyroid stimulating hormone (TSH), which may reflect reduced thyroxin concentration, was assessed in 497,458 newborns in California in 1998. A total of 800 perchlorate water measurements were used to classify California communities as exposed (>5 μg/L) or unexposed. Results were stratified by age at TSH collection because of the normal postbirth TSH surge, and because water sources and perchlorate exposure can change soon after birth.
Results:
In TSH samples collected within 24 hours of birth, the odds ratio for a TSH greater than 25 μU/mL in exposed communities was 1.53 (P < 0.0001). After 24 hours, the odds ratio for a TSH more than the 95th percentile was 1.27 (P < 0.0001).
Conclusion:
These findings suggest that perchlorate is associated with increased neonatal TSH levels.
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