Seasonal variation in the prevalence of preeclampsia.

Objective: To determine whether there is a seasonal impact on the prevalence of preeclampsia in the tropical climate of Bangkok.

Material And Method: Medical records of all singleton pregnant women who delivered in the authors' institution between 2008 and 2009 were reviewed. The meteorological variables during the study period were obtained from database of the Thai Meteorological Department. The period of study was then divided into two main seasons: monsoon and dry seasons. The rates of preeclampsia occurring in the two seasons, based on the date of conception and date of delivery, were compared.

Results: Data of 7,013 gravidas were included for analysis. Of these, 327 (4.7%) developed preeclampsia. The monsoon season had lower mean maximum temperature (37.0 degrees C vs. 38.1 degrees C, p = 0.114), was more humid (77.0% vs. 68.7%, p < 0.001) and had higher daily rainfall (196.5 mm vs. 37.0 mm, p < 0.001) than dry season. Women who conceived in the dry season were at greater risk to develop preeclampsia than those who conceived in the monsoon season (5.3% vs. 3.7%, adjusted OR 1.51; 95% CI 1.18-1.93). The preeclampsia rates of women who delivered in both seasons were not significantly different: 5.0% in the dry season vs. 4.3% in the monsoon, p = 0.178.

Conclusion: There is a seasonal impact on the prevalence of preeclampsia based on the time of conception, but not the time of delivery. The rate of preeclampsia is significantly higher when conception occurs in the dry season.