Abstract
Background: Although previous studies have examined the preterm birth (PTB) risk due to ambient temperature extremes including heat and cold events, there is little available epidemiological evidence on the effects of temperature variation (TV). This study aimed to investigate the relationship between inter- and intraday TV and PTB in Shenzhen, China. Methods: A total of 1,388,994 live singleton births were collected from January 2003 to December 2012, from the Shenzhen Birth registry system. Daily temperature range (DTR) was defined as the difference between the highest and lowest recorded daily temperature. Intraday TV was defined as the maximum daily diurnal temperature range (Max-DTR) in a given week. Inter-day TV was defined as the maximum increase or decrease in daily mean temperature between days t and t-1 in a given week; either an increase (Temp-inc) or a decrease (Temp-dec). We used Cox proportional hazards models to estimate TV-related PTB risks during the first trimester, the second trimester, and in late pregnancy. Findings: The maximum values for DTR, Temp-inc, and Temp-dec were 17° C, 8° C and 11° C, respectively. The greatest TV-related PTB risk occurred in the second trimester, with 5.8% (95%CI: 3.3%, 8.3%), 23.7% (95%CI: 19.6%, 27.9%), and 4.4% (95%CI: 1.8%, 7.1%) differences per 1° C increase in Max-DTR, Temp-inc, and Temp-dec, respectively. Greater TV was associated with elevated PTB risk during the warm season, but Temp-inc was negatively associated with PTB during the cold season. The TV-PTB association was modified by maternal education and chronic conditions. Interpretation: Sharp temperature variation is a likely risk factor for PTB. Policy makers and clinicians should recognize the potential role of temperature variation in the etiology of PTB so that interventions can be designed to protect pregnant women and their fetuses against extreme temperatures. Funding: This work was supported by the National Key R&D Program of China (Grant No: 2018YFA0606200). Declaration of Interest: We declare that there is no competing financial interests. Ethical Approval: The study protocol was approved by the medical ethics committee of School of Public Health, Sun Yat-sen University. The data used were anonymized and so individual patient consent was not required.
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