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

Van Zyl, Gideon (2012-12)

Thesis (MMed)--Stellenbosch University, 2012.

Thesis

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.

AFRIKAANSE OPSOMMING: Agtergrond - Preeklampsie is ‘n multi-sisteem siekte wat gekenmerk word deur hipertensie en proteinurie. Dit word slegs gedurende swangerskap aangetref - gewoonlik na 20 weke. Dit is steeds een van die voorste oorsake van moederlike en fetale morbiditeit en mortaliteit. Terwyl die oorsaak van preeklampsie steeds onbekend is, dui die belangrikste teorië op versteurde plasentale ontwikkeling en funksionering vroeg in swangerskap. Sekere navorsers het ook die moontlikheid van ‘n seisonale patroon in die voorkoms van preeklampsie ondersoek. ‘n Seisonale patroon is wel identifiseer, maar dit is slegs gebasseer op die datum van verlossing en die resultate tussen studies wissel. Doel - Ons primêre doel was om die seisonale patroon in die insidensie van preeklampsie te ondersoek oor ‘n tydperk van een jaar en dan die datum van bevrugting te vergelyk met die datum van diagnose en verlossing. Metodiek - Ons het ‘n retrospektiewe beskrywende studie gedoen oor al die pasiënte met preeklampsie wat tydens 2010 by Tygerberg Hospitaal verlos is. Preeklampsie is gediagnoseer as hipertensie met geassosieerde proteinurie met aankoms na 20 weke. Die name van die pasiënte is verkry uit die kraamsaal-registers en data is versamel en op ‘n datastel aangebring. Data is primer geanaliseer in terme van die seisoen van verlossing en die seisoen waartydens die laaste maandstonde plaasgevind het. Die seisoene is as volg geklassifiseer : somer vanaf die 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. Die data is geanaliseer met die SPSS sagteware (Statistical Package for Social Science). Diskrete data is vergelyk deur die relatiewe risiko’s te bereken met vertrouensintervalle van 95%, sowel as die chi2 toets. Fisher se eksakte toets is gebruik om ratios te vergelyk waar die verwagte waarde van enige sel in ‘n 2-by-2 tabel minder as 5 is. Die gemiddeldes van normaal-verspreide aaneenlopende data is vergelyk deur die analise van variance. Die mediane van aaneenlopende data wat nie normaal versprei was nie, is bereken met die non-parametriese Mann-Whitney-U-toets. ‘n P-warde van <0,05 is beskou as statisties betekenisvol, waar van toepassing. Resultate - Die piek –insidensie van preeklampsie was gedurende die wintermaande, met 32.2% van alle gevalle. Dit was betekenisvol hoër as die gedurende die somer, waar slegs 169 (17.17%) van gevalle verlos is. Toe ons die data analiseer na gelang van die datum van laaste menstruasie (en gevolglik bevrugting), het ons gevind dat 292 (29.7%) van die pasiënte wat preeklampsie ontwikkel het, het hul laaste maandstonde gedurende die lente ervaar. Die piek-insidensie was gedurende November. Daarteenoor is die laagste insidensie gevind in pasiënte met ‘n laaste menstruasie in die winter, met slegs 218 (22.2%) pasiënte. Gevolgtrekking - Ons het die vorige bevinding by Tygerberg Hospitaal van ‘n seisonale patroon in die ontwikkeling van preeklampsie bevestig. Ons het ook bevestig dat dit nie die datum van diagnose en verlossing is wat’n rol speel nie, maar wel die datum van laaste maandstonde en bevrugting.

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