Prediction of survival for preterm births by weight and gestational age: retrospective population based study

Abstract

Objective: To produce current data on survival of preterm infants. Design: Retrospective population based study. Setting: Trent health region. Subjects: All European and Asian live births, stillbirths, and late fetal losses from 22 to 32 weeks' gestation, excluding those with major congenital malformations, in women resident in the Trent health region between 1 January 1994 and 31 December 1997. Main outcome measures: Birth weight and gestational age specific survival for both European and Asian infants (a) known to be alive at the onset of labour, and (b) admitted for neonatal care. Results: 738 deaths occurred in 3760 infants born between 22 and 32 weeks' gestation during the study period, giving an overall survival rate of 80.4%. The survival rate for the 3489 (92.8%) infants admitted for neonatal care was 86.6%. For European infants known to be alive at the onset of labour, significant variations in gestation specific survival by birth weight emerged from 24 weeks' gestation: survival ranged from 9% (95% confidence interval 7% to 13%) for infants of birth weight 250-499 g to 21% (16% to 28%) for those of 1000-1249 g. At 27 weeks' gestation, survival ranged from 55% (49% to 61%) for infants of birth weight 500-749 g (below the 10th centile) to 80% (76% to 85%) for those of 1250-1499 g. Infants who were large for dates (≥27 weeks' gestation) had a slightly reduced, but not significant, predicted survival. Similar survival rates were observed for Asian infants. The odds ratio for the survival of infants from a multiple birth compared with singleton infants was 1.4 (1.1 to 1.8) Survival graphs for infants admitted for neonatal care are presented by sex. Conclusion: Easy to use birth weight and gestational age specific predicted survival graphs for preterm infants facilitate decision making for clinicians and parents. It is important that these graphs are representative, are produced for a geographically defined population, and are not biased towards the outcomes of particular centres. Such graphs, produced in two stages, allow for the changing pattern of survival of infants from the start of the intrapartum period to immediately after admission for neonatal care. Birth weight and gestational age specific predicted survival graphs for preterm infants facilitate decision making for clinicians and parents. Survival graphs should be representative and not biased towards the outcomes of particular centres. Period specific graphs allow for the changing pattern of survival from the start of the intrapartum period to the immediate period after admission for neonatal care. Causes of preterm delivery in singletons may lead to a poorer survival rate (controlled for gestation and birth weight) than those precipitated by multiple pregnancy. Survival graphs need regular updating to allow for improvements in survival of infants.