SURVIVAL OF VERY-LOW-BIRTH-WEIGHT AND VERY PRETERM INFANTS IN A GEOGRAPHICALLY DEFINED POPULATION

Objective: To determine in a geographically defined population 1 year survival of infants with a birthweight of less than 1500 g or gestatio nal age less than 32 weeks, and to establish the effect of postnatal a ge on predicted survival. Design: Cohort analysis of 72 427 births to Welsh residents in 1993-94. Deaths were identified using the All Wales Perinatal Survey, a population-based surveillance of mortality betwee n 20 weeks of gestation and 1 year of age. Main outcome measures: Birt hweight- and gestation-specific infant mortality, and the effect of po stnatal age, gender, and multiple pregnancy on predicted survival. Res ults: In normally formed infants 1 year survival at 24-25 weeks gestat ion was 35%, compared to 75% at 27-28 weeks, and 95% at 30-31 weeks. I n infants with a birthweight of 500-699 g 1 year survival was 18% comp ared to 70% at 800-999 g, and 97% at 1300-1499 g. The chances of survi val improved markedly with increasing postnatal age; at 24-25 weeks ge station it was 35% at birth, 50% at 12 h, 66% at 7 days and 78% at 4 w eeks. Infant mortality was higher in males, but multiple pregnancy had no effect. Conclusions: Up-to-date birthweight- and gestation-specifi c survival rates are essential for predicting the outcome of a newborn infant. The rapid change in the chances of survival with increasing p ostnatal age emphasises especially the importance of revising the pred iction as the infant gets older, particularly during the first few day s of life.