Is perinatal mortality still a good indicator of perinatal care?

The increasing influence of very immature infants on perinatal mortality rates (PMR) led us to question the usefulness of this parameter in assessing perinatal care. To examine this further we have compared the incidence of perinatal asphyxia amongst mature babies (greater than or equal to 35 weeks gestation) for two geographically-defined populations of over 500,000 people. Both areas have a teaching hospital-based maternity service and comparable perinatal mortality rates. The incidence of severe post-asphyxial encephalopathy showed a marked excess in one population (1.93 vs 0.61 per 1000 births), which was not obviously explicable. Taken in conjunction with the figures for stillbirth in labour, this represented a 2.8 times greater risk for either fetal death in labour or severe asphyxial insult. It would appear that perinatal mortality rates do not accurately reflect important differences in those perinatal outcomes most likely to be affected by perinatal care.