Revised definition of pre-eclampsia.

Different measures of raised blood pressure were analysed in 16,211 singleton pregnancies to determine the most effective way of identifying pre-eclampsia. Increments from baseline in the first half of pregnancy were considered as well as absolute levels. A combination of a high maximum diastolic pressure with a large increase from baseline was better for identifying a group with pre-eclamptic features than either measurement on its own. A first diastolic pressure below 90 mm Hg, a subsequent increase of at least 25 mm Hg, and a maximum reading of at least 90 mm Hg gave appropriate criteria. These were applied to a second set of 15,624 singleton pregnancies and successfully identified a group with pre-eclamptic features. Fewer women were identified as pre-eclamptic than with criteria modified from an existing definition widely used in Britain. The women excluded by the new criteria had the features of mild chronic hypertension rather than pre-eclampsia. The new definition is simple to use but like all other definitions of pre-eclampsia cannot be precise.