Blood Trihalomethane Concentrations and Blood Pressure during and after Pregnancy: A Cohort Study in China

Trihalomethanes (THMs), the leading species of disinfection byproducts in chlorinated tap water, have demonstrated cardiovascular toxicity. However, the association between THM exposure and blood pressure (BP) among pregnant women remains unclear. This study included 1456 women from a Chinese prospective birth cohort. We determined blood THM concentrations [chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (TBM)] across pregnancy trimesters (<i>n</i> = 3642) and repeatedly measured BP throughout pregnancy (<i>n</i> = 5816) and during postpartum (<i>n</i> = 1062). Blood concentrations of TCM and chlorinated THMs (Cl-THMs; the sum of TCM, BDCM, and DBCM) in the second, but not first, trimester were positively associated with gestational diastolic BP and mean arterial pressure (MAP). Additionally, women with higher second-trimester blood concentrations of brominated THMs (the sum of BDCM, DBCM, and TBM) and total THMs (TTHM; the sum of 4 THM) had an increased risk of experiencing a sharply rising MAP throughout pregnancy. Second-trimester blood concentrations of TCM, Cl-THMs, and TTHMs were positively associated with the risk of hypertension during pregnancy, particularly among women carrying male fetuses. However, blood concentrations of THMs were unrelated to postpartum BP. In summary, THM exposure in the second trimester may be associated with elevated BP and a greater risk of hypertension during pregnancy.