Abstract

Background
Severe pre-eclampsia (SPE) is the second cause of maternal death in developed countries. The literature suggests different risk factors for early- and late-onset pre-eclampsia. SPE is usually related to the early-onset type. Pre-eclampsia rate exhibits seasonal variation. However, the weather-SPE association is still unknown. We examined the associations between maternal exposure to meteorological parameters after conception and SPE.

Methods
From 2008 to 2011, all deliveries of women living in the Yvelines area, France, have been prospectively registered. Meteorological measurements from weather stations scattered inside Yvelines were averaged on two exposure windows: early-pregnancy (30 days after conception) and first-trimester (90 days after conception). The relationship between SPE and season of conception was also examined. Hierarchical complementary log-log regression models were used to estimate the weather-SPE association.

Results
SPE was diagnosed in 526 (0.8%) out of 63 633 singleton pregnancies. Increasing temperature or sunshine across both windows was associated with increased SPE risk. Early-pregnancy minimum temperature showed the strongest effect with adjusted odds ratio (OR) per 1 degree Celsius: 1.03 [95% confidence interval (CI) 1.01, 1.04]. The risk of SPE was higher when conception was in summer as compared to winter (OR 1.53, 95% CI 1.27, 1.85). Effect estimates showed only small variations in sensitivity analyses.

Conclusions
Our findings of a weather impact during early pregnancy on SPE may provide a new clue for understanding the causes of pre-eclampsia. Further investigation into the biologic mechanisms for this finding is required.