Association between ambient particulate matter and preterm birth stratified by temperature: A population-based pregnancy cohort study

A growing body of literature reports associations between exposure to particulate matter with aerodynamic diameters ≤2.5 μm (PM_2.5) and 2.5–10 μm (PM_10-2.5) during pregnancy and preterm birth (PTB). However, the role of ambient temperature in PM-PTB associations was rarely investigated. In Israel, we used Maccabi Healthcare Services data to establish a population-based cohort of 381,265 singleton births reaching 24–42 weeks’ gestation and birth weight of 500–5000 g (2004–2015). Daily PM and ambient temperature predictions from a satellite-based spatiotemporal model, at a 1 × 1 km spatial resolution, were linked to the date of birth and maternal residence. Mixed effects Cox regression models, adjusted for covariates, with a random intercept at the mother level were used to assess associations between mean exposure during pregnancy and PTB. We found that exposure to PM_2.5 was positively associated with PTB when the average exposure during pregnancy was either low (first quintile) or high (fifth quintile), compared to exposure in the 2nd-4th quintiles, with hazard ratios (HRs) 1.18 (95% confidence interval [CI], 1.13–1.24) and 1.07 (95% CI, 1.02–1.12), respectively. The results revealed effect modification of temperature. For mothers exposed to low (below median) average temperature during pregnancy, HRs of PTB were 0.93 (95% CI, 0.87–1.00) and 1.21 (95% CI, 1.14–1.29) for the first and fifth PM_2.5 quintiles, respectively, when compared to the 2nd-4th quintiles. However, a reverse trend was indicated for high-temperature pregnancies, where the corresponding HRs were 1.48 (95% CI, 1.39–1.58) and 0.92, (95% CI, 0.96–0.98). In conclusion, consideration of climatic factors can provide new insights into the risk of PTB as a result of exposure to PM_2.5 during pregnancy.