To estimate the incidence and predictors of severe obstetric morbidity. Development of definitions of severe obstetric morbidity by literature review. Case-control study from a defined delivery population with four randomly selected pregnant women as controls for every case. All 19 maternity units within the South East Thames region and six neighbouring hospitals caring for pregnant women from the region between 1 March 1997 and 28 February 1998. 48 865 women who delivered during the time frame. There were 588 cases of severe obstetric morbidity giving an incidence of 12.0/1000 deliveries (95% confidence interval 11.2 to 13.2). During the study there were five maternal deaths attributed to conditions studied. Disease specific morbidities per 1000 deliveries were 6.7 (6.0 to 7.5) for severe haemorrhage, 3.9 (3.3 to 4.5) for severe pre-eclampsia, 0.2 (0.1 to 0.4) for eclampsia, 0.5 (0.3 to 0.8) for HELLP (Haemolysis, Elevated Liver enzymes, and Low Platelets) syndrome, 0.4 (0.2 to 0.6) for severe sepsis, and 0.2 (0.1 to 0.4) for uterine rupture. Age over 34 years, non-white ethnic group, past or current hypertension, previous postpartum haemorrhage, delivery by emergency caesarean section, antenatal admission to hospital, multiple pregnancy, social exclusion, and taking iron or anti-depressants at antenatal booking were all independently associated with morbidity after adjustment. Severe obstetric morbidity and its relation to mortality may be more sensitive measures of pregnancy outcome than mortality alone. Most events are related to obstetric haemorrhage and severe pre-eclampsia. Caesarean section quadruples the risk of morbidity. Development and evaluation of ways of predicting and reducing risk are required with particular emphasis paid on the management of haemorrhage and pre-eclampsia.
