Independent and Combined Effects of Heatwaves and PM2.5 on Preterm Birth in Guangzhou, China: A Survival Analysis

Abstract

BACKGROUND: Both extreme heat and air pollution exposure during pregnancy have been associated with preterm birth; however, their combined effects are unclear. OBJECTIVES: Our goal was to estimate the independent and joint effects of heatwaves and fine particulate matter [PM <2:5 lm in aerodynamic diameter (PM 2:5 )], exposure during the final gestational week on preterm birth. METHODS: Using birth registry data from Guangzhou, China, we included 215,059 singleton live births in the warm season (1 May-31 October) between January 2015 and July 2017. Daily meteorological variables from 5 monitoring stations and PM 2:5 concentrations from 11 sites were used to estimate district-specific exposures. A series of cut off temperature thresholds and durations (2, 3, and 4 consecutive d) were used to define 15 different heatwaves. Cox proportional hazard models were used to estimate the effects of heatwaves and PM 2:5 exposures during the final week on preterm birth, and departures from additive joint effects were assessed using the relative excess risk due to interaction (RERI). RESULTS: Numbers of preterm births increased in association with heatwave exposures during the final gestational week. Depending on the heatwave definition used, hazard ratios (HRs) ranged from 1.10 (95% CI: 1.01, 1.20) to 1.92 (1.39, 2.64). Associations were stronger for more intense heatwaves. Combined effects of PM 2:5 exposures and heatwaves appeared to be synergistic (RERIs >0) for less extreme heatwaves (i.e., shorter or with relatively low temperature thresholds) but were less than additive (RERIs <0) for more intense heatwaves. CONCLUSIONS: Our research strengthens the evidence that exposure to heatwaves during the final gestational week can independently trigger preterm birth. Moderate heatwaves may also act synergistically with PM 2:5 exposure to increase risk of preterm birth, which adds new evidence to the current understanding of combined effects of air pollution and meteorological variables on adverse birth outcomes. https://doi.

Acute associations between heatwaves and preterm and early-term birth in 50 US metropolitan areas: a matched case-control study

“…Specifically, heatwave associations were larger in magnitude among Hispanic and non-Hispanic black mothers compared to non-Hispanic white mothers. In several previous studies, investigators reported positive associations between heatwaves and preterm birth, with larger magnitudes compared to our study [ 9 , 11 , 13 , 19 – 22 , 42 ]. In the current study, we observed only a slight overall increase in the risk of preterm birth for certain heatwave definitions, and most estimates were close to the null.…”

“…However, no consistent epidemiological evidence suggests that extreme temperature should have a greater impact on births later in gestational age (e.g., late preterm (34–36 weeks) and early-term birth (37–38 weeks)) compared to those in early gestation (e.g., extremely preterm (< 28 weeks) and very preterm (28–32 weeks)). Some studies observed stronger associations of temperature among early preterm birth [ 11 , 14 , 19 ], while others found the opposite [ 22 , 43 ].…”

“…However, the magnitude of association varied considerably, and it is unclear what factors influence this relationship. A few studies also found that heatwaves, conceptually defined as consecutive days of high ambient temperature, were positively associated with preterm birth in the last week before delivery [ 19 – 22 ], and that these associations persisted even after adjusting for current day temperatures [ 23 ]. Unfortunately, synthesizing results from heatwave studies is challenging due to differences in location, study design, and heatwave definition.…”

Advances in Air Quality Research – Current and Emerging Challenges

“…those of PM2.5, have been shown to have been in the 1980's twice as high, compared with the corresponding pollutant levels in the same region during the second decade of the 21st century (Kukkonen et al, 2018). Wang et al (2020) presented that PM2.5 exposure strengthened the effect of moderate heat waves (short or only moderate temperature rise) associated with preterm births during January 2015 -July 2017 in Guangdong province, China. However, during the intensive heat waves, the effects were not additive.…”

Heatwaves and PM2.5: Sometimes-Surprising Associations with Preterm Birth

“… 3 , 4 A retrospective cohort study published in Environmental Health Perspectives looked at the relationship between fine particulate matter ( ) combined with heatwaves and the risk of preterm birth in Guangzhou, China. 5 …”