Although there are excellent studies examining factors responsible for preterm delivery in general, there is a scarcity of data describing factors specifically associated with delivery of the immature newborn infant. Our purpose is to characterize these factors in order to determine what may be done to limit preterm delivery rate of extremely low birth weight infants. Obstetric variables responsible for the birth of 338 live in-born immature neonates in a large single perinatal center were determined. We were unable to affect 65% of these pregnancies because there was no chance for intervention prior to admission in 63% of these mothers, and 66% had nonpreventable obstetric complications responsible for delivery. The median time interval from admission to delivery was 7 hours. Mortality was significantly higher in those delivered within 7 hours. We also found that neonatal mortality was twice as high in infants born to women with a previous perinatal loss. The clinical implications of these results are discussed.