The effect of preterm birth on the serial growth of the corpus callosum and cerebellar vermis and the earliest time of detected impairment were studied by cranial ultrasonography in 61 very low birth-weight (VLBW) infants (<33 weeks gestation; <1500 gms) admitted to a single regional level III NICU from 1998 to 2000 at Christchurch Hospital, New Zealand. Sonograms were performed twice, >7 days apart, in the first 2 weeks of life, at 6 weeks, and at term equivalent. The length of the corpus callosum and vermis was measured on midline sagittal images, and growth rates calculated in mm per day. The relation between corpus callosum growth rates and neurodevelopmental outcome at 2 years of age was examined. The corpus callosum elongated at a normal rate of 0.21 mm/day from birth to 2 weeks but slowed to 0.11 mm/day in weeks 2-6. A reduction in growth rate of the corpus callosum was detected by 6 weeks in 96% of infants of 23-33 weeks’ gestation, and it persisted to term equivalent in the majority. Some improvement in growth rate of the corpus callosum occurred in 15% of infants after 6 weeks, but only in VLBW infants born after 28 weeks gestation. Retardation in growth of the vermis was correlated with corpus callosum growth impairment. Motor delay and cerebral palsy at 2 years of age were associated with under-development of the corpus callosum between 2 and 6 weeks after birth. 
COMMENT. Corpus callosum white matter injury occurs at the time of birth in almost all infants born prematurely at 23-33 weeks’ gestation. The impairment in growth of the corpus callosum and also the vermis of the cerebellum is detectable by bedside ultrasound by 6 weeks of age or earlier, if the damage occurs prenatally. Neuroprotective strategies such as mild hypothermia are best implemented in the NICU as soon after birth as possible. VLBW infants with reduced growth of the corpus callosum detected at 2 to 6 weeks after birth are at increased risk of psychomotor developmental delay and cerebral palsy.
Allometric scaling of brain growth of preterm infants on serial MRIs was used to demonstrate a deficit in cortical surface-area expansion relative to brain volume with increasing prematurity (Kapellou O et al, reviewed by Allin M.) . Slower rates of cortical surface-area growth correlated with developmental delay at 2 years of age, especially in boys. An abnormal subcortical white-matter connectivity is proposed, rather than loss of neurons, to explain the neurological and cognitive deficits in preterm babies.