Hypothyroxinemia of prematurity and the risk of cerebral white matter damage

Objective: Infants with hypothyroxinemia of prematurity (HOP) are at increa sed risk for neurodevelopmental dysfunction. Infants born near the end of t he middle trimester are also at increased risk for an echoluceney (EL) in t he cerebral white matter, which reflects white matter damage and is the cra nial ultrasound abnormality that best predicts neurodevelopmental dysfuncti on. We postulated that some of the increased risk of neurodevelopmental pro blems associated with HOP reflects an increased risk of EL. Study design: We studied 1414 infants weighing 500 to 1500 g who were born at 4 medical centers between 1991 and 1993. The infants had thyroxine blood levels measured during the first weeks of life, at least 1 of 3 cranial ul trasound scans performed at specified postnatal intervals, and their own an d their mother's hospital charts reviewed. Infants were classified by wheth er or not their first thyroxine level placed them in the lowest quartile am ong all infants in this sample (ie, <67.8 nmoVL, our definition of HOP, equ ivalent to <5.3 mu g/dL). Results: After adjusting for such potential confounders as low gestational age and measures of illness severity, infants with HOP had twice the risk o f EL as their peers with higher thyroxine levels. Conclusion: Our findings are consistent with the hypothesis that a "normal" blood thyroxine level protects infants born near the end of the middle tri mester against the risk of cerebral white matter damage.