Total brain white matter is a major determinant of IQ in adolescents born preterm.

OBJECTIVE: In preterm infants, white matter (WM) abnormalities detected on magnetic resonance imaging (MRI) at term-age are associated with early developmental delay. We set out to study this association in adolescents born pre-term, by examining intellectual outcome in relation to markers of brain injury, focusing on the effects of WM reduction.
METHODS: Seventy-nine participants were recruited and assessed at a mean age of 16 years: 49 adolescents born preterm (<32 weeks' gestation) with a wide spectrum of brain injuries (including 22 with no identifiable brain injury at birth) and 30 term-born controls. Data collected included: brain MRI scans, full-scale intelligence quotient (IQ) scores, educational attainments, and behavioral scores. Measures of WM reduction included total volume, cross-sectional area of the corpus callosum (CC), and ventricular dilatation. Cerebellar volumes and neuroradiological ratings were also included.
RESULTS: WM volume and IQ were reduced in the preterm groups (both with and without brain injury). Total WM volume and CC area jointly explained 70% of IQ variance in the adolescents born preterm, irrespective of the presence or severity of brain abnormalities detected at birth or on follow-up MRI. This relationship was not seen in controls. Importantly, correlations were also found with real-world measures of academic achievement and behavioral difficulties.
INTERPRETATION: Preterm birth has a long-term effect on cognition, behavior, and future academic success primarily as a consequence of global brain WM reduction. This emphasizes the need for early therapeutic efforts to prevent WM injury and promote or optimize its development in preterm neonates.