Serial Thyroid Function Test in Very Low Birth Weight Neonates

Abstract

Thyroid dysfunction is more common in preterm and low birth weight infants, and may be missed if thyroid function test (TFT) is not repeated. Thus, we attempted to study the pattern of thyroid function among very low birth weight (VLBW) infants with birth weight less than 1,500 g by serial TFTs. Serum free thyroxine (FT4) and thyrotropin (thyroid-stimulating hormone [TSH]) levels of VLBW infants were tested on fifth to seventh days of life and repeated after 4 weeks of age. Based on serial FT4 and TSH results, abnormal TFT was classified into four groups—transient hypothyroxinemia of prematurity (THOP), transient hyperthyrotropinemia (THT), delayed TSH rise, and overt congenital hypothyroidism (CH). Stata 15.1 (Stata Corp, Texas, United States) was used for analysis. Ninety-six VLBW infants were enrolled with mean gestational age of 30.5 ± 2.7 weeks and median (interquartile range) birth weight of 1,200 (317) g. Out of 96 cases, 30 (31.2%) infants had abnormal TFT. Ten (10.4%) infants had THOP, 7 (7.3%) infants had THT, 11 (11.5%) infants had delayed TSH rise, and 2 (2.1%) infants had overt CH. There were no significant differences in demographic profile and clinical characteristics between neonates with normal and abnormal TFTs. Five infants required levothyroxine supplementation (two infants with overt CH and three infants with delayed TSH rise). VLBW neonates have higher incidence of CH and delayed rise of TSH in this study. In resource-limited settings, repeating TFTs at least once after 4 weeks of age may be suggested to identify delayed rise of TSH which may need intervention.