In a recently released issue of Pediatrics, Dr. Steven Korzeniewski and colleagues examine (10.1542/peds.2017-0697) 10 year neurodevelopmental outcomes of very premature infants born below 28 weeks gestation. The authors were able to compare infants with severe and less severe fetal growth restriction with their counterparts who were not growth restricted on a broad battery of behavioral, socio-developmental and cognitive tests. Unique aspects of this study were the long duration of follow-up, the extraordinarily comprehensive evaluation performed, and the excellent retention rate of those eligible (92%, total of 889 children assessed).
The authors focused on growth restriction as the main variable of interest, and used birth weight z score to describe the degree of growth restriction. A z score is a measure of how many standard deviations above or below the population mean a score or measure is. Rather than using a percentile cutoff (as in the definition of small for gestational age), the authors chose to categorize infants as severely growth restricted or less severely growth restricted by z score. This created the opportunity to look at degrees of fetal growth restriction in comparison to those preterm infants of normal weight. The authors note that describing growth restriction is not straightforward, and there is no generally agreed upon method of distinguishing a small baby with normal growth (for his or her genetic potential) from an infant who is small due to disordered growth. But the results of this fascinating study suggest that growth restriction, and degree of growth restriction, are highly meaningful: it appears to be either a marker for, or a causative factor of, lower scores on multiple neurocognitive tests, with greater risk for autism and poor social skills.
What a long way science has to go here! We can support parents and re-double our efforts to proactively identify resources and services for former preterm infants, now recognizing that being very small at birth (fetal growth restriction) is an added risk factor. But primary prevention will only follow a much deeper etiologic understanding of fetal growth restriction, and this article’s discussion describes multiple tantalizing opportunities and ideas for future exploration.