The effect and its critical window for ambient temperature and humidity in pregnancy on term low birth weight

As common meteorological factors in daily life, there is limited evidence for the effect of ambient temperature and humidity during pregnancy on the risk of term low birth weight. Furthermore, little is known about the interaction of ambient temperature and humidity on TLBW. The objective of the study was to explore the effect of ambient temperature, humidity during pregnancy, and their interaction on the risk of TLBW and, moreover, to identify exposure critical window. We recruited 6640 infants and their mothers to build a birth cohort study in Jinan City, China, from January 2018 to December 2019. The associations between temperature and humidity during pregnancy and TLBW were estimated by generalized additive model, logistic regression model, and interaction analysis, and the critical window was identified by the distributed lag non-linear model. The incidence of TLBW was 1.36% for the infants in the birth cohort. TLBW was related to the low level of temperature and humidity in the whole pregnancy, compared with the moderate level and the adjusted ORs were 4.44 (1.65-11.42) and 6.23 (1.92-21.39), respectively. The indicators of the interaction analysis of temperature and humidity were not statistically significant. For the low level of humidity, the association with TLBW was statistically significant at first to sixth gestational weeks, and the maximum OR in male infants (3.95, 1.70-9.16) was higher than that in females (1.96, 1.06-3.63). For the low level of temperature, we failed to find significant association with TLBW at each gestational week. The low level of temperature and humidity during pregnancy could increase the risk of TLBW. There was no statistical interaction between temperature and humidity on TLBW. Moreover, the early stage of pregnancy was the critical window for humidity exposure, in which the boys had a greater effect.