Preterm delivery places the immature brain at risk of intraventricular and periventricular hemorrhage, and diffuse hypoxic-ischemic damage. The natural progression of these lesions and their effect on development is unclear. Stewart and colleagues followed infants who survived birth before 33 weeks of gestation and have recently reported on their status at adolescence.
A group of 105 infants was enrolled for follow-up assessment of neurocognitive and behavioral functions. The participants underwent neurologic and cognitive assessment at one, four and eight years of age. At 14 to 15 years of age, 103 patients were traced, of which 72 underwent further assessment. The patients available for follow-up did not differ in any respect from those who could not be traced or declined to participate in the study. A control group consisted of 47 infants born at term in the same hospital during the same time period (between 1979 and 1980) as the cohort participants. At 14 to 15 years of age, 21 persons continued to participate in the study. The cohort and control groups underwent extensive assessment, including collection of data from parents on health, behavioral and educational achievement. In addition to clinical and neurologic examination, reading age was assessed, and participants completed a battery of cognitive and behavioral testing. Magnetic resonance imaging (MRI) scans were obtained in all participants. Two neuro-radiologists, who were unaware of the participants' histories, prepared the MRI reports.
In the cohort group, 40 of the 72 participants had abnormal MRI scans and a further 15 had equivocal scans. Only one abnormal and five equivocal scans were reported among the 21 participants in the control group. The most common abnormalities involved thinning or atrophy of the corpus callosum, ventricular dilatation and white matter lesions. Abnormalities on MRI scans did not appear to be related to birth weight, gestational age at birth, Apgar score or mode of delivery. Previous results of neonatal ultrasound examinations performed on the cohort participants were compared to MRI results, revealing that the sensitivity of hypoxic-ischemic injury on neonatal ultrasonography was 22 percent for later abnormal or equivocal MRI scans. Conversely, neonatal ultrasonography had a positive predictive value of 92 percent and a specificity of 94 percent. The cohort group had a lower reading age and more neurologic impairments, and those with abnormal MRI scans had more behavioral abnormalities than those in the control group.
The authors conclude that infants born before 33 weeks' gestation have a high prevalence of structural brain abnormalities, and more than one half have abnormal MRI scans. The functional effect of these abnormalities appears to be manifested more often in behavioral abnormalities than in neurologic impairments.