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.
Keywords
very low birth weight infant - thyroid function tests - congenital hypothyroidism
- premature infants
