Serial Thyroid Function Test in Very Low Birth Weight Neonates

Birendra Pradhan,Deepti Damayanty Pradhan,Sonali Sahoo,Manas Kumar Nayak,Santosh Kumar Panda,Soumini Rath

doi:10.1055/s-0041-1731337

Abstract

AbstractThyroid 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.

Highlights

Congenital hypothyroidism (CH) is one of the preventable causes of neurodevelopmental impairment, if diagnosed and treated early.[1]
transient hypothyroxinemia of prematurity (THOP)—low free thyroxine (FT4) and normal thyroid-stimulating hormone (TSH) in the initial test which got normalized on repeat test
transient hyperthyrotropinemia (THT)—elevated TSH and normal FT4 in the initial test which got normalized on repeat test

Summary

Introduction

Congenital hypothyroidism (CH) is one of the preventable causes of neurodevelopmental impairment, if diagnosed and treated early.[1]. Immaturity of thyroid hormone synthesis and metabolism, increased need for thyroxine by preterm neonates, and stormy course of very low birth weight (VLBW) infants influence thyroid hormone production and regulation.[4,5] CH, transient hypothyroxinemia of prematurity (THOP), delayed rise of thyroid-stimulating hormone (TSH), received November 29, 2020 accepted after revision May 20, 2021. Kim et al performed serial thyroid function tests (TFTs) in[180] premature infants less than 32 weeks and found thyroid dysfunction in 28.9% of them.[7] Armanian et al found abnormal TFTs in 58.7% of VLBW infants.[8] evidence-based guidelines for thyroid function monitoring in preterm neonates have not been established. THOP—low FT4 and normal TSH in the initial test which got normalized on repeat test. THT—elevated TSH and normal FT4 in the initial test which got normalized on repeat test. Delayed TSH rise—normal FT4 and TSH in initial test and only elevated TSH in repeat test

Methods

Results

Discussion

Conclusion