A Study on Normalization of Hypothyroxinemia in Neonates below 34 Weeks of Gestation

Objectives: The aim of the study was to estimate the time required for normalization of hypothyroxinemia of prematurity in neonates below 34 weeks of gestation. Material and Methods: A retrospective study was conducted in neonates born below 34 weeks of gestation, between January 2015 and December 2016. Data were collected on free thyroxine (fT4) and thyroid-stimulating hormone (TSH) levels, tested on days 3, 14, 28, and 42. Gestational age, birth weight, use of antenatal steroids, mechanical ventilation, and various preterm morbidities, along with development at 18 months of corrected age, were comparatively analyzed in neonates with and without hypothyroxinemia. The median time for normalization of fT4 in all these variables was estimated. Results: On day 3, low fT4 was noted in 69 (37.7%) out of 183 neonates born below 34 weeks of gestation; all had normal TSH levels. Hypothyroxinemia showed statistically significant association with gestational age, birth weight, antenatal steroid use, respiratory distress syndrome, invasive ventilation, shock, sepsis, patent ductus arteriosus (PDA), anemia during stay in neonatal intensive care unit, and development at 18 months. Median time for normalization was 14 days in most of the neonates, and 28 days in those with <28 weeks of gestational age, weight of <1000 g and with shock, anemia, and PDA. Two infants with hypothyroxinemia received therapy with levothyroxine at 6 weeks for a short duration, as TSH was high. Conclusion: Hypothyroxinemia of prematurity takes 14–28 days to normalize based on maturity, weight, and illnesses. This study recommends serum fT4 testing at 2 weeks of life, provided congenital hypothyroidism was ruled out by 3–4 days of life, using direct blood spot card metabolic screening.