STUDY DESIGN: Data on 69,452 neonates with birth weights of 500 to 2000 g were obtained from electronic files of birth certificates. Hospitals' perinatal services were classified as level 1, 2, or 3 (level 3 refers to tertiary referral centers).

RESULTS: The likelihood of birth outside revel 3 hospitals decreased from 1968 to 1994, with an average annual decrease of 24% for infants weighing 500 to 1500 g and 20% for infants weighing 1501 to 2000 g. After 1974, birth in a hospital with level 3 services was associated with a lower risk of dying. The strength of this association increased in the 1990s.

CONCLUSIONS: In North Carolina the proportion of infants weighing <2000 g born outside a hospital with level 3 neonatal services declined from 1974 through 1994. After 1974, birth in a hospital with level 3 neonatal services was associated with lower neonatal mortality.