Falling incidence of hypoxic-ischaemic encephalopathy in term infants.

OBJECTIVE: To examine trends in the incidence of hypoxic-ischaemic encephalopathy over a 13-year period.

DESIGN: A retrospective analysis of medical records of all infants admitted in the years 1976-1980 and 1984-1988.

SETTING: A large non-teaching district health authority in central England.

SUBJECTS: Infants admitted to a district general hospital neonatal unit with clinical features of hypoxic-ischaemic encephalopathy.

MAIN OUTCOME MEASURES: Incidence of three grades of hypoxic-ischaemic encephalopathy, handicap and mortality.

RESULTS: During the first 5-year period the overall incidence of hypoxic-ischaemic encephalopathy was 7.7 per 1000 live births with 2.6 per 1000 live births being severely affected (grades II and III). In the second 5-year period the overall incidence was 4.6 per 1000 live births with 1.8 per 1000 live births being severely affected. The difference in the overall rate is statistically significant. Of the infants with severe encephalopathy 61% had Apgar scores below 4 at 1 min and 60% were born by instrumental or operative delivery.

CONCLUSIONS: The fall in incidence of hypoxic-ischaemic encephalopathy has occurred during a period of falling perinatal mortality rate. It was instructive to find that infants born vaginally and without obstetric intervention formed a larger fraction of the severely affected infants in the later period.