Short-term effects of heatwave and PM2.5 exposure on the risk of preterm birth in Guangzhou, China

Abstract

PDS 72: Environmental health issues in LMIC, Exhibition Hall (PDS), Ground floor, August 28, 2019, 10:30 AM - 12:00 PM Background: Extreme temperatures and air pollution both have significant burden on birth outcomes, however, the effects of short-term exposure to extreme heat and its interaction with air pollution on preterm birth (PTB) remain unclear. Objectives: To investigate the short-term effects of different definitions of heatwaves (n=12) and PM2.5 exposure on PTB and further explore interactive effects on the PTB risk. Methods: Using birth certificate data from Guangzhou, China, we included 249,489 singleton live births that occurred in the warm season (May 1-October 31) between January 2015 and July 2017. Daily average concentrations of PM2.5 from 11 monitoring stations and meteorological variables from five weather stations were used to estimate district-specific exposures. A series of cut-off temperatures and durations were used to define heatwaves. Distributed lag models (DLMs) using Cox proportional hazard models were used to estimate the effects of heatwave and PM2.5 exposure during the last week before delivery, and their additive interactive effect on PTB was assessed by using the relative excess risk due to interaction (RERI). Results: For most heatwave definitions used, an increased risk of PTB was observed for the women experienced at least one heatwave event in the last gestational week, with hazard ratios (HRs) of PTB ranging from 1.24 (95% CI: 1.01-1.52) to 1.78 (1.48-2.15). The effect estimates increased with the intensity of heatwave and the effects on later PTB (weeks 35-36) were stronger than those on earlier PTB (weeks 28-34). We observed weak effects of PM2.5 during the last week, and a negative additive interaction between heatwaves and PM2.5 exposure on PTB, with the RERIs<0. Conclusions: Exposure to heatwaves late in gestation is associated with a greater risk of PTB in Guangzhou. The finding of the negative interaction between short-term heatwaves and PM2.5 exposure on PTB warrants further investigation about the potential underlying mechanisms.