Is improved survival of very-low-birthweight infants in the 1980s and 1990s associated with increasing intellectual deficit in surviving children?

To investigate whether the decrease in mean birthweight of the smallest infants surviving with a very low birthweight (VLBW) in the past two decades is associated with an increase in intellectual deficit rates, we compared the results obtained in two different follow-up studies: one included a cohort of children of VLBW (<1500g; n=102, 52% male) born in the early 1980s; the other included a cohort of children of extremely low birthweight (ELBW; <1000g; n=183, 46% male) born in the mid-1990s. Intellectual development was evaluated in both cohorts. McCarthy Scales of Children's Abilities were used in the cohort from the early 1980s; Wechsler's Preschool and Primary Scale of Intelligence--Revised was used in the cohort from the mid-1990s. The children were assessed at age 4-5 years, and a control group was included for each of the two studies. Mean scores in the measures of intelligence found at the assessment were recalculated to standard deviation scores from the two control groups. We found no difference in the standard deviation scores between the two cohorts despite the mean birthweight being 353g (p<0.001) lower in the cohort from the mid-1990s, and the overall survival rate of infants of VLBW having increased. Our results suggest that the improved survival of the smallest babies in the 1980s and 1990s has been achieved without an increase in the intellectual deficit in the surviving children.