Prenatal predictors of mortality in very preterm infants cared for in the Australian and New Zealand Neonatal Network

Aim: To identify antenatal and perinatal risk factors for in-hospital mortality of babies born within the Australian and New Zealand Neonatal Network (ANZNN). Methods: Data were collected prospectively as part of the ongoing audit of high-risk infants (birth weight < 1500 g or gestation < 32 weeks) admitted to all level III neonatal units in Australia and New Zealand. Antenatal and intrapartum factors to 1 min of age were examined in 11 498 infants with gestational age > 24 weeks. Risk and protective factors for mortality were derived from logistic regression models fitted to 1998-9 data and validated on 2000-1 data. Results: For the whole cohort of infants born between 1998 and 2001, prematurity was the dominant risk factor, infants born at 25 weeks having 32 times greater odds of death than infants born at 31 weeks. Low birth weight for gestational age also had a dose-response effect: the more growth restricted the infant the greater the risk of mortality; infants below the 3rd centile had eight times greater odds of death than those between the 25th and 75th centiles. Male sex was also a significant risk factor (odds ratio (OR) 1.55, 95% confidence interval (Cl) 1.31 to 1.82). Maternal hypertension in pregnancy was protective (OR 0.46, 95% Cl 0.36 to 0.50). The predictive model for mortality had an area under the receiver operating characteristic curve of 0.82. Conclusions: Risk of mortality can be predicted with good accuracy with factors up to the 1 min Apgar score. By using gestation rather than birth weight as the main indicator of maturity, these data confirm that weight for gestational age is an independent risk factor for mortality.