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.