Association of Ambient Temperature in Early Pregnancy with Placental Markers and HDP Risk

Abstract Background Hypertensive disorders of pregnancy (HDPs) affect ∼10% of pregnancies globally and remain a leading cause of maternal morbidity and mortality. Temperature exposure during early pregnancy may influence HDP risk, yet the physiological pathways remain unclear. As climate change intensifies, identifying modifiable environmental risks is critical to maternal health. Methods We conducted a prospective cohort study of 5,693 pregnant women enrolled at Nanjing Drum Tower Hospital (2017-2020). After exclusions, 3,354, 3,359, and 3,382 women remained for analyses of uterine artery pulsatility index (UtA-PI), placental growth factor (PlGF), and pregnancy-associated plasma protein A (PAPP-A), respectively. Exposure was defined as mean daily temperature from conception to 11-13.5 weeks gestation. Covariates included humidity, air pollutants, and population characteristics. Nonlinear exposure-response relationships were modeled with restricted cubic splines (RCS), and categorized associations were estimated via generalized linear models (GLM). Results A nonlinear association was observed between early pregnancy temperature and HDP risk, rising sharply above 23 deg C. PlGF followed an inverted U-shape, peaking at ∼18 deg C. UtA-PI and PAPP-A showed U-shaped patterns with nadirs at 18 deg C. GLM analyses indicated increased HDP risk with high temperatures (>65th percentile), with odds ratios of 1.81 (UtA-PI), 2.05 (PlGF), and 1.68 (PAPP-A). High temperature was associated with elevated UtA-PI (3.32% increase; 95% CI: 0.50%-6.21%) and reduced PlGF (-14.71%; 95% CI: -19.38% to -9.77%). Cold exposure (<35th percentile) showed weaker, inconsistent associations, with marginal increases in PAPP-A (5.10%; 95% CI: 0.09%-10.84%). Conclusions Temperature exposure in early pregnancy may increase HDP risk by impairing placental perfusion and function. Our findings highlight the need for climate-adaptive maternal health strategies and integration of environmental risk into prenatal care. Key messages • Early pregnancy heat exposure increases HDP risk and adversely impacts placental perfusion and function markers. • Integrating environmental risk assessments and temperature mitigation strategies into prenatal care is crucial for safeguarding maternal health in the context of climate change.