Objective: There is an urgent need for a bedside method to assess the effectiveness of neonatal therapies designed to improve cerebral development in very low birth-weight infants. The aim of this study was to assess the impact of preterm birth on the serial growth of the corpus callosum and how soon it could be detected after birth with cranial ultrasound.
Methods: We recruited 61 very low birth-weight infants admitted to a single regional level III NICU from 1998 to 2000. Study infants had 2 cranial sonograms > or = 7 days apart in the first 2 weeks of life and further sonograms at 6 weeks and at term equivalent. At each time point, the length of the corpus callosum and cerebellar vermis was measured on midline sagittal images, with growth rates calculated in millimeters per day. We compared growth of corpus callosum and cerebellar vermis in individuals, between birth age groups, and with corrected gestational age. We used antenatal growth rate of the corpus callosum of 0.2 to 0.27 mm/day as a reference. Relationships between corpus callosum growth rates and neurodevelopmental outcome at 2 years of age (corrected) were also examined.
Results: Growth of the corpus callosum was normal in most infants during the first 2 weeks of life but slowed after this (0.21 mm/day from 0-2 weeks vs 0.11 mm/day for weeks 2-6). Slowing of corpus callosum growth below expected reference range was consistently detectable by age 6 weeks for 96% of infants born between 23 and 33 weeks' gestation. Although some improvement in growth rate was observed for 15% of infants after 6 weeks, this was confined to infants born after 28 weeks. Vermis length correlated strongly with corpus callosum length. By 2 years of age, serious motor delay and cerebral palsy were associated with poorer growth of the length of the corpus callosum between 2 and 6 weeks after birth.
Conclusions: The effect of preterm birth on growth of the corpus callosum is detectable by 6 weeks after delivery in preterm infants born at gestations of 23 to 33 weeks. Reduced growth of the corpus callosum in weeks 2 to 6, places these infants at elevated risks of later psychomotor delay and cerebral palsy.