Adverse reproductive outcomes and outdoor air temperature in Haidian District, Beijing

Abstract

Background Adverse reproductive outcomes have been described as having seasonality caused by maternal exposure to outdoor air temperature during pregnancy. However, the direction of the temperature effect and the critical exposure time windows are unclear. Aims We investigated the effect of temperature on preterm birth (PTB) and birth defect (BD) in Haidian district, Beijing. The concerned exposure time windows for PTB and BD were the last trimester of pregnancy and the first trimester of plus one month before pregnancy, respectively. Methods We estimated the nonlinear and delayed effects of temperature within each month (meaning the 1st, 2nd and 3rd month before birth or after pregnancy, and the month before pregnancy) by distributed lag nonlinear models using Logistic time-series regression including potential confounders. We calculated the odd ratios (OR) of PTB or BD in association with each monthly average temperature. Results An elevated temperature on a day within all the three months before birth would announce its effect on PTB after 0-2 and 8-18 days. A declined temperature on a day within the 1st, 2nd or 3rd month before birth would announce its effect on PTB after 2-9 and 21-26 days, 4-12 and 22-26 days or 0-3 and 11-22 days, respectively. A declined temperature on a day within the month before or the 3rd month after pregnancy would lead to BD after 1-12 and 24-27 days; a declined temperature on a day within the 1st or 2nd month after pregnancy would lead to BD immediately after 0-1 day. The most noticeable OR of PTB was 1.18 (0.78, 1.78) with a 5? increase in average temperature of the 1st month before birth, of BD was 0.51 (0.19, 1.38) with a 5? increase in average temperature of the 3rd month after pregnancy. Conclusions Both high and low temperature in the last trimester of pregnancy led to preterm birth. Only low temperature in the first trimester of pregnancy and the month before pregnancy led to birth defect.