Determinants of neurobehavioral outcome in low-birth-weights infants.

The relative importance of (1) birth weight, gestational age, and head circumference at birth, and (2) appropriateness of birth weight and head circumference to gestational age in the predictability of neurobehavioral outcome was evaluated in 127 low-birth-weight infants at 7 months of age. Lower absolute birth weights, shorter gestational ages, and smaller head circumferences at birth correlated with poorer outcome (Bayley Scales of Infant Development and abnormal neurologic examination) at the corrected chronologic age of 7 months (r = .28 to .42, all P less than .005). The incidence of low scores on the Mental Development Index and of severe neurologic deficit was significantly higher in small head circumference for gestational age infants than in appropriate head circumference for gestational age infants (both, P less than .05). In the absence of small head circumference, small for gestational age infants had similar incidences of low Bayley scores and abnormal neurologic examinations as did appropriate for gestational age infants. These observations suggest that head circumference at birth may be the single most important variable for subsequent neurobehavioral outcome, and that both birth weight and gestational age may simply be markers of fetal head growth in their relationship to later outcome.