Objective: To determine whether improvement in the survival rate of infants with a birthweight of less than 1501 g was accompanied by an increase in the rate of neurological impairment or disability among the survivors.
Design, setting and patients: Two cohorts of consecutive very low birthweight infants (birthweight less than 1501 g) in one tertiary perinatal centre were followed prospectively to eight years of age; for both cohorts, comparison groups of children of birthweight more than 1501 g were randomly selected from hospital births.
Interventions: The first cohort was born before the introduction of assisted ventilation (1966-1970), the second after assisted ventilation was well established (1980-1982).
Main outcome measures: Comparisons between cohorts, at eight years of age, of the survival rates and the rates of severe sensorineural impairments and disabilities.
Results: The survival rate for very low birthweight infants to eight years of age almost doubled between these cohorts, from 37.1% to 67.8% (odds ratio [OR], 3.4; 95% confidence interval [CI], 2.5-4.7; chi 2 = 57.6; P much less than 0.0001). The biggest gain was the increase in non-disabled survivors at eight years of age, from 52.6% in the first cohort to 80.8% in the second cohort (OR, 3.5; 95% CI, 2.2-5.7; chi 2 = 26.7; P less than 0.0001). Furthermore, the rate of severe disabilities in survivors fell substantially, from 13.6% to 4.1% (OR, 0.31; 95% CI, 0.14-0.69; chi 2 = 8.3; P less than 0.01). Of specific impairments, the rate of severe sensorineural deafness fell substantially (3.2% to 0%: OR, 0.14, 95% CI, 0.02-0.81; chi 2 = 4.8; P less than 0.05), as did the rate of severe intellectual impairment (13.0% to 2.7%: OR, 0.25; 95% CI, 0.11-0.57; chi 2 = 10.7; P less than 0.002). Only the rate of cerebral palsy increased, but not significantly (2.6% to 6.8%; OR, 2.6; 95% CI, 0.89-7.6; chi 2 = 3.0).
Conclusions: It has been possible to improve the survival rate of very low birthweight infants over time without increasing the number of severely disabled survivors. Whether the long-term outcome for these infants is continuing to improve with more recent advances in perinatal care remains to be determined.