The association of apparent temperature with fetal growth: A birth cohort study in Beijing, China

The physiological characteristics of pregnant women and fetuses make them more susceptible to unfavorable temperature conditions. This cohort study in Beijing, China, involved 23,182 singleton pregnant women. Apparent temperature (AT; a composite index of temperature and relative humidity) matched to the participants' residential addresses. Fetal growth was assessed using ultrasound parameters, transformed into gestational-ageand gender-adjusted standard score (Z-score). Association between AT and fetal growth analysed by mixed linear models showed that both high and low AT exposures significantly negatively affected fetal head, abdominal and femur length development and significantly decreased fetal weight in utero. For instance, at <= 23 weeks, both lower and higher AT were associated with a decrease in abdominal circumference (AC) Z-scores by 0.16 (95 % confidence interval (95 % CI):0.20, -0.11). At 24-31 weeks, lower and higher AT decreased AC Z-scores by 0.13 (95 % CI:0.17, -0.09) and 0.09 (95 % CI:0.13, -0.05), respectively. At 32-40 weeks, lower and higher AT decreased AC Z-scores by 0.03 (95 % CI:0.06, 0.01) and 0.06 (95 % CI:0.09, -0.02), respectively. This study contributes to a deeper understanding of the vulnerabilities of pregnant women and fetuses to urban heat exposure, to safeguard public health and promote sustainable development.