Risk factors for major obstetric haemorrhage.

The factors associated with major obstetric haemorrhage were analyzed using data relating to 37,497 women delivered in 1988 in National Health Service maternity units in the North West Thames Region, UK. Four hundred ninety-eight cases (1.33%) were complicated by haemorrhage of 1000 ml or more. Intrinsic factors associated with significant risk ratios (99% confidence intervals) included placental abruption 12.6 (7.61-20.9), placenta praevia 13.1 (7.47-23.0), multiple pregnancy 4.46 (3.01-6.61) and obesity 1.64 (1.24-2.17), but not high parity. Significant risk factors related to obstetric management and delivery included retained placenta 5.15 (3.36-7.87), induced labour 2.22 (1.67-2.96), episiotomy 2.06 (1.36-3.11) and birthweight 4 kg or more 1.90 (1.38 to 2.60). Among the 59 women who lost 1000 ml or more in association with a spontaneous vaginal delivery with an intact perineum, significant risk ratios (99% confidence intervals) were retained placenta 13.7 (5.92-31.8) and induced labour 2.35 (1.11-4.98). These data provide a more comprehensive assessment of risk factors for potentially life threatening haemorrhage in British obstetric practice than is possible using maternal mortality statistics. The hazards of well known factors such as multiple pregnancy, abruption, placenta praevia and caesarean delivery were confirmed but attention is drawn to the potential risk of haemorrhage associated with obesity or a large baby and to that associated with retained placenta in women classified as 'low risk'.