Objective: The goal was to identify, among extremely low birth weight (<or=1000 g) live births, the proportion of infants who were unimpaired at 18 to 22 months of corrected age.
Methods: Unimpaired outcome was defined as Bayley Scales of Infant Development II scores of >or=85, normal neurologic examination findings, and normal vision, hearing, swallowing, and walking. Outcomes were determined for 5250 (86%) of 6090 extremely low birth weight inborn infants.
Results: Of the 5250 infants whose outcomes were known at 18 months, 850 (16%) were unimpaired, 1153 (22%) had mild impairments, 1147 (22%) had moderate/severe neurodevelopmental impairments, and 2100 (40%) had died. Unimpaired survival rates varied according to birth weight, from <1% for infants <or=500 g to 24% for infants 901 to 1000 g. The regression model to predict unimpaired survival versus death or impairment for live births (N = 5250) indicated that 25.3% of the variance was derived from infant factors present at birth, including female gender, higher birth weight, singleton birth. The regression model to predict unimpaired survival for discharged infants indicated that most of the variance was derived from combined effects of major neonatal morbidities, neonatal interventions, and maternal demographic features (15.7%) and only 8.5% was derived from infant factors present at birth.
Conclusions: Although <1% of live-born infants of <or=500 g survive free of impairment at 18 months, this increases to almost 24% for infants of 901 to 1000 g. Female gender, singleton birth, higher birth weight, absence of neonatal morbidities, private health insurance, and white race increase the likelihood of unimpaired status.