Thyroid Dysfunction in Very-Low-Birth-Weight Premature Neonates: A Systematic Review of Published Evidence

Congenital hypothyroidism is the most common preventable cause of mental retardation in children and should be diagnosed and treated at the earliest time. The prevalence of congenital hypothyroidism is high in preterm infants with low and very low birth weight.
A systematic literature review was conducted using PubMed, Scopus and Google Scholar databases to 19 April 2014. We did not consider any time limitation; English-language papers were included. Irrelevant studies were set aside after studying their title, abstract, and full text. Two reviewers extracted the data; besides, the third reviewer checked their extracted data. In final, the data extracted from related studies.
Findings: Normal serum thyroid-stimulating hormone (TSH) at third to sixth days of birth in low- and very-low-birth-weight preterm infants did not indicate normal thyroid function. In addition, TSH level of more than 10 mIu/l at the second week of the birth did not have a diagnostic value. A TSH level of 10-15 mIu/l, after a normal TSH value, posed the diagnosis of hypothyroidism with delayed TSH rise. Serum levels of free-T4 (FT4) and T4 would be normal at 2 to 8 weeks after the birth.
It is recommended to repeat the screening of preterm newborns with low and very low birth weight by measuring TSH and FT4 levels simultaneously at two, six and ten weeks after the birth; the threshold of TSH = 10 mIu/l should be considered to select positive and suspected cases of the disease.