Association of Ambient Air Pollution and Temperature Exposure with Placental Abruption: A Nested Case-Control Study Based on Live Birth Registrations.

Background: Placental abruption, a rare disorder of unclear etiology, lacks evidence to illustrate its relationship with exposure to air pollution and temperature.

Objective: This study aimed to investigate the association between exposure to ambient pollutants and temperatures and placental abruption to identify susceptible time windows and subpopulations.

Methods: A nested case-control study was based on a live birth registration database in Chongqing, the largest Chinese municipality in China, from 2018 to 2022. The placental abruption cases were each matched with four controls by maternal age at delivery, gestational week, gravidity, parity, and delivery date. Six ambient pollutants [particulate matter (PM) with aerodynamic diameter $\le 2.5\mu m$ (${\mathrm{PM}}_{2.5}$), PM with aerodynamic diameter $\le 10\mu m$ (${\mathrm{PM}}_{10}$), ${\mathrm{NO}}_2$, CO, $O_3$, and ${\mathrm{SO}}_2$] and temperature were estimated using machine learning algorithms. A conditional logistic regression model analyzed associations of exposure to air pollution and temperature with placental abruption in five time windows (prepregnancy, the entire pregnancy, and each of the 3 trimesters). Stratification analyses were applied to examine potential modifiers including gravidity, parity, mothers' residential area (urban/rural), pandemic experience, and delivery season.

Results: After data quality control, 798 cases were identified and matched with 3,192 controls. An exposure relationship was identified between ${\mathrm{NO}}_2$ during the pregnancy period and placental abruption ($p<0.001$). In comparison with the first quartile level of ${\mathrm{NO}}_2$, the odds ratios (ORs) of abruption associated with exposure to the second, third, and fourth quartile levels of ${\mathrm{NO}}_2$ were 1.42 [95% confidence interval (CI): 1.03, 1.96], 1.90 (95% CI: 1.30, 2.76), and 2.27 (95% CI: 1.39, 3.71), respectively. The association for ${\mathrm{NO}}_2$ exposure existed in the 3 trimesters but not prepregnancy. Exposure to locally extreme low temperatures ($<\text{fifth}$ percentile) in the third trimester was associated with increased risks of abruption ($\text{OR}=3.68$; 95% CI: 1.67, 8.08) in comparison with locally moderate temperatures (25th-75th percentile). Stratified analysis showed no statistical significances within the effect modifiers.

Discussion: Based on a large-scale live birth record, the study suggested that exposure to air pollutants, mainly ${\mathrm{NO}}_2$, during pregnancy may be a substantial risk factor for placental abruption. https://doi.org/10.1289/EHP14714.