Associations between Meteorological Conditions and Fetal Growth and Gestational Duration in Cohort Studies

Abstract

Background: Epidemiological studies have indicated associations between variations in ambient temperature during pregnancy and fetal growth and gestational duration. Such results remain debated. We aimed to evaluate associations between meteorological conditions and pregnancy outcomes in two French mother-child cohorts. Methods: 5324 women were recruited during pregnancy between 2002-2006. Average daily ambient temperature and relative humidity were provided by Météo France. We studied medium (each trimester and whole pregnancy) and short (weekly from week 1 to week 6 before delivery) term exposure windows. Associations with birth weight (BW), gestational duration (weeks) and preterm delivery (PD) were investigated using linear and Cox proportional hazards regressions. Non-linearity of the relationships was tested using penalized splines. Results were adjusted for temperature and relative humidity during all trimesters of exposure (correlation was taken care of), season and year of conception, cohort and individual confounders. Results: BW varied positively and linearly with temperature in the first trimester of pregnancy (p=0.07, ß=35g for a 5°C increase) and negatively with temperature in the second and third trimesters (resp. ß=-34, p=0.06 and ß=-38, p=0.03). BW varied negatively and linearly with relative humidity in the second and third trimesters of pregnancy (resp. ß=-55, p=0.01 and ß=-31, p=0.13, for a 10% change in relative humidity). Gestational duration decreased when temperature was higher than 15°C and when relative humidity was higher than 85% in the third trimester of pregnancy, suggesting a non-linear relationship (p<0.05). An increased risk of PD was observed for relative humidity levels over 80% in the third trimester of pregnancy. Conclusion: Our results suggest a negative effect of temperature and relative humidity, particularly in the second and third trimesters on BW, as well as in the third trimester on gestational duration and risk of PD.