With the increasing survival of extremely preterm (EP) birth infants in the surfactant era, the longer-term outcome of infants born at the threshold of viability has become a vital topic of study. The goal of this investigation was twofold. First, while taking into account the influence of sociodemographic confounds, we wished to investigate neuropsychological outcome differences between two groups of EP preschoolers: 23-24 weeks (n = 20), and 25-26 weeks' (n = 21) gestation at delivery. Second, we wished to explore whether, within the population of EP preschoolers, gestational maturity accounts for a unique portion of the variance in neuropsychological outcome, over and above the variance explained by ante-, peri-, and neonatal complications, or treatment factors. The findings revealed group differences, ranging from .70 to .80 of a standard deviation in general intellectual abilities, nonverbal intelligence, and global motor performance, in favor of the more mature EP group. Additionally, gestational maturity was found to explain a unique portion of the variance in global intellectual and motor abilities. These findings are interpreted from the perspective that gestational age is an index of the vulnerability of the central nervous system to disruption of developmentally regulated processes.

In this study we examined the association between intrauterine growth, indexed either as a categorical variable or continuous dimension, and neuropsychological outcome, in a very low birth weight (VLBW) sample of 143 preschoolers. When the commonly used split at the 10th percentile rank was applied to classify intrauterine growth restriction (IUGR), we found that the growth restricted group (n = 25) exhibited significantly poorer performance in the global motor domain, but not on any other neuropsychological measure. In contrast, when adequacy of intrauterine growth was indexed by standardized birth weight, a continuous dimension, this early risk factor explained a unique portion of the variance in global cognitive abilities and visuospatial skills, as well as in global, fine, and gross motor skills. These findings are consistent with recent magnetic resonance imaging data disclosing global neurodevelopmental changes in the brains of preterm infants with IUGR. When cases classified with IUGR (<10th percentile) were excluded, the relationship between adequacy of intrauterine growth and global cognitive abilities remained significant despite range restriction. Hence, an association between appropriateness of intrauterine growth and global intellectual outcome may be observed even within the population of VLBW preschoolers with adequate standardized birth weight.

Among postnatal anthropometric indices, preschool stature, rather than head circumference, remains a consistent correlate of preschool outcome in preterm children, highlighting the contribution of general physical development to neuropsychological performance. Further investigation of the underlying mechanisms likely involves exploration of complex relationships between postnatal nutrition, growth hormone levels, body and brain development, and neuropsychological functioning.

We studied the associations between early postnatal growth gains and neuropsychological outcome in very preterm-born children. Specifically, we wished to establish whether relationships exist between gains in head circumference (relative to gains in body-weight or length), from birth to hospital discharge, and intellectual, language, or motor, performance at preschool age. We used data from 127 preschoolers, born <33 weeks, all graduates of the William Beaumont Hospital Neonatal Intensive-Care Unit (NICU) in Royal Oak, MI. Cognitive, motor, and language outcomes were evaluated using the Wechsler Preschool and Primary Scales of Intelligence-Revised, Peabody Developmental Scales - 2(nd) Edition, and the Preschool Language Scale - 3(rd) Edition, respectively. Differences between Z-scores at birth and hospital discharge, calculated for three anthropometric measures (head circumference, weight, length), were variables of interest in separate simultaneous multiple regression procedures. We statistically adjusted for sex, socioeconomic status, birth weight, length of hospitalization, perinatal complications, and intrauterine growth. Examination of the relationships between anthropometric indices and outcome measures revealed a significant association between NICU head growth and global intelligence, with the Z-difference score for head circumference accounting for a unique portion of the variance in global intelligence (ηp(2) =.04). Early postnatal head growth is significantly associated with neuropsychological outcome in very preterm-born preschoolers. To conclude, despite its relative brevity, NICU stay, often overlapping with the end of 2(nd) and with the 3(rd) trimester of pregnancy, appears to be a sensitive developmental period for brain substrates underlying neuropsychological functions.

The modest twin disadvantage on language and visual processing tasks at preschool-age could not be readily attributable to socioeconomic or perinatal variables. The possibility of biological or social twinning-related phenomena as mechanisms underlying the observed performance gaps are discussed. (JINS, 2016, 22, 865-877).