Studies using routine data versus specific data collection: What can we learn about the epidemiology of eclampsia and the impact of changes in management of gestational hypertensive disorders?

Evidence-based changes in practice, services and policy may impact on the spectrum of pregnancy hypertensive disorders at many levels. Demonstration of clinical benefit relies on assessment of changes in disease incidence or complications. Two main alternative observational methodologies may be used to investigate changes in disease incidence; the first using routinely collected data and the second with specially designed prospective data collection. Routinely collected data have been shown to have limitations; the introduction of specific prospective data collection systems, such as the UK Obstetric Surveillance System, allow for an increased robustness and range of disease incidence and outcome studies, and thus enhance our ability to investigate the impact of changes in practice. The comparison of recent national studies using these systems shows that the incidence of eclampsia has declined in the UK, but that the incidence of eclampsia is higher in the Netherlands and Scandinavia. The decrease in the UK is clearly due to a fall in the number of women with diagnosed pre-eclampsia who go on to have an eclamptic fit; figures from the Netherlands and Scandinavia suggest that eclamptic fits in the group with prior diagnosed pre-eclampsia are less effectively prevented and this may be the reason for the observed higher incidence of eclampsia. This information may help to further inform management and preventive strategies, and illustrates the additional benefits of international comparisons of severe maternal morbidities.