Ambient cold exposure amplifies the effect of ambient PM₁ on blood pressure and hypertensive disorders of pregnancy among Chinese pregnant women: A nationwide cohort study

Background: Little evidence exists regarding the combined effect between ambient temperature and air pollution exposure on maternal blood pressure (BP) and hypertensive disorders of pregnancy (HDP).

Objectives: To assess effect modification by temperature exposure on the PM₁-BP/HDP associations among Chinese pregnant women based on a nationwide study.

Methods: We conducted a cross-sectional country-based population study in China, enrolling 86,005 participants from November 2017 to December 2021. BP was measured with standardized sphygmomanometers. HDP was defined according to the American College of Obstetricians and Gynecologists' recommendations. Daily temperature data were obtained from the European Centre for Medium-Range Weather Forecasts. PM₁ concentrations were evaluated using generalized additive model. Generalized linear mixed models were used to examine the health effects, controlling for multiple covariates. We also performed a series of stratified and sensitivity analyses.

Results: The pro-hypertensive effect of PM₁ was observed in the first trimester. Cold exposure amplifies the first-trimester PM₁-BP/HDP associations, with adjusted estimate (aβ) for systolic blood pressure (SBP) of 3.038 (95 % CI: 2.320-3.755), aβ for diastolic blood pressure (DBP) of 2.189 (95 % CI: 1.503-2.875), and aOR for HDP of 1.392 (95 % CI: 1.160-1.670). Pregnant women who were educated longer than 17 years or living in urban areas appeared to be more vulnerable to the modification in the first trimester. These findings remained robust after sensitivity analyses.

Conclusions: First trimester maybe the critical exposure window for the PM₁-BP/HDP associations among Chinese pregnant women. Cold exposure amplifies the associations, and those with higher education level or living in urban areas appeared to be more vulnerable.