Treatment of Transient Hypothyroxinemia of Prematurity Does Not Improve Neurodevelopment at Two Years of Age.

Aim: Transient hypothyroxinemia of prematurity (THOP) has been associated with suboptimal neurodevelopment. We aimed to assess neurodevelopment in very preterm infants with treated and untreated THOP.

Methods: This study was a multicentre, cohort study, based on prospectively collected data in four French level III neonatal intensive care units. Infants born before 32 weeks of gestation between 2009 and 2020 who underwent a thyroid function test were included. THOP was defined as low free thyroxine and unelevated thyroid stimulating hormone. Infants were classified as no THOP, treated THOP, and untreated THOP. The primary outcome was suboptimal neurodevelopment at 2 years of age evaluated by clinical examination.

Results: Three hundred and seventy-three infants (54% male) born at a median gestational age of 28 weeks of gestation were included. There was no significant difference in neurodevelopment at 2 years of age when comparing the no THOP to the THOP group (Odds Ratio (OR) 1.4, 95% confident Interval (CI) 0.8-2.3) nor when comparing the treated with the untreated THOP group (OR 0.8, 95% CI 0.3-1.9). Results remained unchanged after adjusting for confounding factors.

Conclusion: In very preterm infants treated THOP was not associated with improved neurodevelopment compared to untreated THOP. Numerous biases could have limited treatment effect.