Objective: To study the effect of L-thyroxine supplementation on neurologic maturation in infants < 30 weeks' gestational age with transient hypothyroxinemia.

Design: Randomized, double-blind, placebo controlled L-thyroxine supplementation trial.

Setting: Level III neonatal intensive care unit.

Subjects: 200 Infants < 30 weeks' gestational age.

Intervention: Subjects were randomly assigned to receive L-thyroxine (8 mg/kg birthweight/d) or a placebo during the first six weeks of life, irrespective of thyroid hormone levels.

Methods: Median nerve somatosensory evoked potentials (SEPs) were recorded, using a mobile SEP recording machine (Neuropack Four Mini, model MEB-5304K - Nihon Kohden, Tokyo, Japan), measuring cortical N1 peak latency at two weeks of age, at term and at six months (corrected) age. Linear regression analysis (BMDP 1R) was used.

Results: Cortical N1 peak latency was not significantly decreased in the L-thyroxine group compared to the placebo group throughout the study period (Table).

Table 1 No caption available.
Full size table

Conclusion: L-thyroxine supplementation during the first six weeks of life did not decrease cortical N1 peak latency in infants of < 30 weeks' gestational age.

Cortical N1 peak latency (ms) in median nerve SEP in relation to L-thyroxine supplementation. Values are mean±SD; Δ L-Thyroxine minus Placebo.