Thyroxine for transient hypothyroxinemia and cerebral palsy in extremely preterm infants

Background: The relationship of thyroxine supplementation for transient hypothyroxinemia of prematurity to the incidence of cerebral palsy (CP) in infants <28 weeks of gestation is unclear. Methods: The incidence of CP at a corrected age of 18 months was compared between infants born in a 3‐year period in which routine measurement of free T4 (FT4) in the blood was not performed (first period, n= 54), and those born in a later 3‐year period in which FT4 was measured (second period, n= 60; mainly at 7 days old), and in which l ‐thyroxine 5–10 µg/kg per day (mean, 9 µg/kg/day) was administered for FT4 levels <0.8 ng/dL. Incidence of CP at 3 years of age was also compared between the same groups. Results: Background clinical factors between the two groups were comparable except for prenatal steroid administration, which was reduced in the second period. Incidence of CP at a corrected age of 18 months was significantly lower in the second period (3.3%) than in the first period (16.6%). Incidence of CP at 3 years of age was also significantly lower in the second period. Multiple logistic regression analysis using factors except thyroxine supplementation, for the total of 114 infants from both groups, found no perinatal factors related to the development of CP at a corrected age of 18 months. Conclusions: Thyroxine supplementation for transient hypothyroxinemia of prematurity may reduce the incidence of CP in extremely preterm infants. Large‐scale randomized controlled trials are essential to determine the effects of thyroxine supplementation in reducing the incidence of CP among extremely preterm infants.