Neonatal outcome associated with singleton birth at 34-41 weeks of gestation.

BACKGROUND Approximately 75% of preterm births are late-preterm (34(0/7) to 36(6/7) weeks gestation). This group has usually been considered as a whole in studies assessing the outcome of these preterm infants by comparison with term infants. However, the respective contribution to prognosis of each week of gestation has not been fully clarified. METHODS A population-based study of 150 426 live-born singleton neonates with gestational ages ranging from 34 to 41 weeks of gestation. RESULTS The rate of severe respiratory disorders (treated by mechanical ventilation and/or nasal continuous positive airway pressure) markedly declined with gestational age from 19.8% at 34 weeks to 0.28% at 39-41 weeks. Between 34 and 38 weeks, each additional week diminished the relative risk (crude or adjusted) of severe respiratory disorders by a factor varying from 2 to 3. The rate of poor prognosis (death and/or severe neurological condition) significantly declined between 34 and 38 weeks and remained stable thereafter. A multivariate analysis showed that antepartum haemorrhage and hypertensive disorders during pregnancy were significantly associated with severe respiratory disorders and poor outcome. Diabetes was an additional factor associated with severe respiratory disorders. CONCLUSIONS Future studies should delineate more precisely the respective contribution of gestational age, maternal complication and induced delivery in the prognosis of infants born between 33 and 39 weeks gestation.