Background Many studies suggest that ambient temperature change is a potental risk factor of low birth weight of newborns.
Objectve The current study evaluates whether ambient temperature change during pregnancy would affect the birth weight of newborns and the risk of low birth weight.
Methods Study subjects were 5 533 single live newborns delivered in the Renmin Hospital of Wuhan University from January 1, 2011 to May 31, 2014. Their maternal sociodemographic data and delivery data were collected. The meteorological data (such as ambient temperature and humidity) and air quality index (AQI) from March 20, 2010 to October 18, 2013 were retrieved from the National Meteorological Information Center and the China National Environmental Monitoring Centre, respectively. A generalized linear model and a logistic regression model were conducted respectively to evaluate the effects of ambient temperature during different trimesters on the birth weight of newborns and the risk of low birth weight. A generalized linear model was fted using natural cubic spline with 3 degrees of freedom for ambient temperature and relatve humidity, and the relatonships between average temperature during different trimesters and birth weight were explored by plotng the exposure-response curve.
Results The average birth weight of newborns was (3201.8±563.5) g, and the incidence rate of low-birth-weight infants was 9.0% (498/5 533) during the observed tme period. The daily mean values of ambient temperature during the frst, second, and third trimesters of the partcipants were (17.5±8.6), (16.4±7.8), and (16.0±8.6)℃, respectvely. By controlling maternal sociodemographic factors and AQI, the increases of birth weight associated with per 1℃ increase of mean ambient temperature were 1.984 g (95%CI:0.240-3.729) and 2.742 g (95%CI:0.868-4.615) for the first trimester and the second trimester, respectively. However, no apparent evidence showed an association between ambient temperature and the risk of low birth weight. The exposure-response curve illustratng the relatonship between mean temperature in the third trimester and birth weight was inverted "U" shaped, and the curve illustratng the relatonship between mean temperature in the frst or second trimester and birth weight was linear.
Conclusion The study findings suggest that the increased birth weight of newborns may be associated with the increased ambient temperature during the frst and second trimesters. No signifcant associaton between ambient temperature change and the low birth weight of newborns is found in this study.
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