Predicting the need for ventilatory support in neonates 30-36 weeks' gestational age

To determine antenatal factors associated with the need for ventilatory support in babies born between 30 and 36 weeks gestational age and use this information to help referring obstetricians decide which mothers need antenatal transfer.

Babies born at Royal Prince Alfred Hospital at 30-36 weeks' gestation inclusive between January 1992 to December 1999 were identified in the obstetric and neonatal databases. Information for a wide range of antenatal factors and respiratory outcomes was extracted. Babies with major congenital anomalies were excluded. Statistical analysis using spss for Windows was then undertaken.

Data were available for 3102 babies. On univariate analysis, seven factors were significant. Lower gestational age, absence of labour, Caesarean section, antepartum haemorrhage, breech presentation and hypertensive disease of pregnancy were associated with increased risk, while threatened premature labour was protective. On logistic regression analysis, gestational age and absence of labour dominated the model. Other significant factors in the model had a relatively minor impact.

The risk of needing ventilatory support according to antenatal risk factors is described for infants born between 30 and 36 weeks. Gestational age and absence of labour were found to be the major determinants of risk. Delivery without labour increased the risk by the equivalent of about 2 weeks of gestation. For example, to avoid a risk > 20%, the cut off is 33 weeks for mothers who labour, but is increased to 35 weeks when there is no labour. Our results should be interpreted with caution, as the patients in a tertiary obstetric unit may not be typical of the wider community.