Seasonal Trend in the Occurrence of Preeclampsia and Eclampsia in Texas

BACKGROUND The pathogenesis of preeclampsia remains poorly understood. Recent investigations have suggested that the incidence varies by season of conception and the season of delivery. A cross-sectional study was conducted to determine whether there was an association between the season of delivery and the prevalence of preeclampsia/eclampsia in Texas. METHODS Retrospective analysis of hospital discharge records of 312,207 women who delivered in Texas in 2007 was performed. This statewide dataset was obtained from the Texas Department of State Health Services (Austin, TX). The season of admission for delivery was the independent variable: winter (December, January, February), spring (March, April, May), summer (June, July, August), and fall (September, October, November). The outcome was preeclampsia or eclampsia as defined by ICD-9-CM codes. Crude and adjusted prevalence odds ratios (OR) were calculated and reported with 95% confidence intervals (CI) and P values. The monthly prevalence of preeclampsia was also examined. RESULTS Seasonal variation was minimal with the lowest prevalence detected in the fall (3.89%) and a peak of 4.1% in the winter. The highest monthly prevalence was found in January (4.4%). After adjusting for maternal age, race, and other potential confounders, women who were admitted in the fall for delivery were 6% less likely than women who were admitted in the winter to have preeclampsia: adjusted OR = 0.94,95% CI: 0.89-0.99, P = 0.02). CONCLUSIONS A weak protective association between delivering in the fall (vs. winter) and the prevalence of preeclampsia was noted in this analysis of a statewide hospital database.