Extreme preterm birth: onset of delivery and its effect on infant survival and morbidity.

OBJECTIVE: To investigate whether correlations could be found between the onset of preterm delivery and infant outcome, that is, survival and major morbidity.
METHODS: The study was a retrospective, hospital-based cohort study. All women with a live fetus on admission, giving birth at 22(+0) to 27(+6) weeks of gestation between 1998 and 2003 were included. The deliveries were subdivided into those that began with either preterm labor, preterm premature rupture of membranes (PROM), or iatrogenic preterm delivery. These groups were compared for survival and survival without major morbidity (intraventricular hemorrhage grade 3-4, periventricular leukomalacia, retinopathy of prematurity grade 3-4, bronchopulmonary dysplasia, or necrotizing enterocolitis) at discharge.
RESULTS: The cause of the preterm birth was preterm labor in 154 of 288 (53%), preterm PROM 83 of 288 (29%), and iatrogenic preterm delivery 51 of 288 (18%). There were 83% liveborn children, and 67% survived until discharge. Survival was lower for preterm PROM (54%) than for preterm labor (75%) and iatrogenic preterm delivery (67%). Multivariable analyses showed that survival was positively associated with gestational age and antenatal steroid treatment. Negative associations concerning survival were found for preterm PROM and being small for gestational age. Survival without major morbidity did not differ significantly between the groups and was positively associated with gestational age and negatively associated with being small for gestational age.
CONCLUSION: Infant survival was significantly lower when the onset of preterm delivery was preterm PROM as compared with preterm labor and iatrogenic delivery. For surviving infants there was no significant difference in major morbidity between the groups. LEVEL OF EVIDENCE: III.