Seasonal variation in preeclampsia – timing of conception vs timing of delivery

[摘要] ENGLISH ABSTRACT: Background - Preeclampsia is a multi-system disease characterized by hypertension and proteinuria in pregnant women at greater than 20 weeks of gestational age. It remains one of the leading causes of maternal and foetal mortality and morbidity.While the cause of preeclampsia is essentially unknown, the important theories strongly implicate disturbed placental function in early pregnancy. Additionally, some researchers have investigated the possibility of a seasonal relationship with the incidence of preeclampsia. Differences in incidences of preeclampsia, examined exclusively on the basis of delivery timing, have also been noted to have seasonal variation, but results have been inconsistent.Objective - Our primary objective was to investigate the seasonal variation in preeclampsia in relation to the timing of conception and the timing of presentation with clinical disease over the period of one year.Methods - We performed a retrospective descriptive study of all women with preeclampsia who delivered at Tygerberg Hospital in 2010. Preeclampsia was diagnosed as hypertension associated with proteinuria after the 20th week of gestation.Names of patients were identified from labour ward records and data was collected and recorded on a data-sheet.Data were primarily analysed in relation to the season of delivery and also the season of the last menstruation. Summer was diagnosed as lasting from summer solstice to autumn equinox, autumn as lasting from autumn equinox until winter solstice, winter as lasting from winter solstice until spring equinox and spring as lasting from spring equinox until summer solstice.The data was analysed using the SPSS software (Statistical Package for Social Science). Discrete data was compared by calculating relative risks with 95% confidence limits, as well as the chi2 test. Fisher's exact test was used to compare ratios where the expected value in any cell of a two-by-two table is less than five. The means of normally distributed continuous data was compared by analysis of variance, while the medians of continuous data which are not distributed normally, where calculated using the non-parametric Mann Whitney u test. A p-value of < 0.05 was considered to be statistically significant, where applicable.Results - The peak incidence of preeclampsia was during winter with 32.2% of all cases occurring during this season. This was significantly higher than during the summer when only 169 (17.17%) cases of preeclampsia were delivered.When we analysed the data looking at the timing of menstruation (and therefore conception), we found that 292 (29.7%) patients that developed preeclampsia had their last menstrual period in the spring, with November the month of peak incidence. The lowest incidence was found in winter, with only 218 (22.2%) patients.Conclusion - We have confirmed a previous finding of a seasonal variation in the occurence of preeclampsia in Tygerberg Hospital. We have also confirmed that this seasonal variation is not only influenced by the timing of delivery, but also by the timing of conception.

[发布机构] Stellenbosch University