Associations Between Blood Heavy Metal Concentrations and Hypertensive Disorders of Pregnancy in the Japan Environment and Children's Study

Background Previous studies reported inconsistent associations between blood heavy metal concentrations and the risk of hypertensive disorders of pregnancy (HDP), potentially due to small sample sizes and variations in exposure levels, timing of blood sampling, and confounding factors. We investigated this association in Japanese women, a population with relatively low metal exposure, to provide a unique perspective in a low‐exposure setting. Methods We included 88 670 pregnant women, with a mean age of 31.2±5.1 years, enrolled in the Japan Environment and Children's Study. We examined the associations between concentrations of heavy metals (lead, cadmium, and mercury) in blood collected during the second or third trimester and HDP, using multiple logistic regression under a Bayesian framework, adjusting for potential effects of confounders including parity, body mass index, smoking, and diet quality. Results The per‐woman incidence of HDP was 2703 (3.1%). The median blood concentrations of lead, cadmium, and mercury were 5.86 (interquartile range, 4.72–7.35), 0.664 (interquartile range, 0.496–0.906), and 3.62 (interquartile range, 2.53–5.17) ng/g, respectively. After adjusting for potential confounders, blood lead, cadmium, and mercury concentrations were positively associated with the odds of HDP. The median odds ratios for HDP in the highest vs lowest quartiles of blood metal concentrations were 1.58 (95% credible interval, 1.39–1.77) for lead, 1.30 (95% credible interval, 1.15–1.45) for cadmium, and 1.15 (95% credible interval, 1.03–1.28) for mercury. Conclusions Higher blood lead, cadmium, and mercury concentrations were associated with HDP in Japanese pregnant women. Our findings suggest that low‐dose exposure to these heavy metals is an underrecognized but important risk factor for HDP, highlighting the need to develop measures to reduce heavy metal exposure.