Prenatal exposure to temperature variability, gestational duration and preterm birth: A nationwide birth cohort with 3 million singleton births in China

Abstract

Background: Little is known about how temperature variability (TV) affects the risk of preterm birth (PTB). Objective: This cohort study aims to evaluate the associations of prenatal TV exposure with gestational age and PTB risk. Methods: This study included 3,012,744 live singleton births from 336 Chinese cities delivered between January 2013 and December 2015. TV exposure, indicating by standard deviation of temperature (SDT) and diurnal temperature range (DTR), were assessed by spatiotemporal models. Cox proportional hazard regression models were used to analyze the associations of PTB risk with TV exposure during the entire pregnancy and specific trimesters. Multivariate linear regressions were used to assess the associations between TV exposure and gestational age. Results: During the entire pregnancy, each 1 °C incremental in SDT and DTR was associated with a reduction in gestational age by 0.98 day (95 % confidence interval (CI), 0.89–1.06) and 0.36 day (95 % CI, 0.32–0.39). These increases in TV were also linked to a 20.1 % higher risk of PTB (hazard ratio [HR]: 1.201; 95 % CI: 1.182–1.233) for SDT and a 7.3 % higher risk of PTB (HR: 1.073; 95 % CI: 1.064–1.081) for DTR. The risk associated with TV was greater for very PTB than moderate and late PTB. Non-linear exposure–response curves indicated a monotonic increase in HRs for PTB with higher TV exposure, with the curves becoming less steep beyond an inflection point. These associations seemed to be more pronounced in women who lived in rural areas and in the climate zone of tropical monsoon, and gave birth in winter compared to their counterparts. Conclusions: TV was associated with higher PTB risk and shortened gestational age in China.

Keywords

• Temperature variability
• Diurnal temperature range
• Standard deviation of the daily temperature
• Climate change
• Preterm birth
• Gestational age