Impact of infants born at the threshold of viability on the neonatal mortality rate in Colorado.

OBJECTIVE: To determine the contribution of infants born at the threshold of viability (< 750 gm) on neonatal mortality in Colorado. STUDY DESIGN: For the period of January 1991 to December 1996, all Colorado live births who expired were evaluated for gestational age, birth weight, gender, hospital level of care, age at time of death, delivery room resuscitation, mechanical ventilation, medical and surgical complications, and serious malformations. RESULTS: Although infants weighing < 750 gm represent only 0.31% of all live births, they account for 46.3% of deaths. While those infants weighing < 500 gm and with a gestation of < 24 weeks almost always died (94.7%), the majority born in the 500- to 745-gm category (55.8%) survived. The vast majority (88.5%) of deaths occurred on the first day of life. A total of 38.4% of births in which the infant weighed < 750 gm occurred outside bona fide regional perinatal centers. CONCLUSION: Future attempts to reduce the Colorado neonatal mortality rate would best focus on the 500- to 750-gm weight group through the re-regionalization of high-risk perinatal care.