Frequency of Thyroid Function Disorders among a Population of Very-Low-Birth-Weight Premature Infants

Background: Thyroid function disorders, particularly congenital hypothyroidism (CHT), are important endocrine dysfunctions associated with permanent morbidities. CHT is more prevalent among preterm low-birth-weight neonates compared to term infants with normal weight. Methods: This prospective cohort study was conducted on 126 very-low-birth-weight (VLBW) neonates referred to the neonatal intensive care units (NICUs) of two tertiary referral hospitals affiliated to Isfahan University of Medical Sciences in Isfahan, Iran during 2012-2014. On day five of birth and two, four, and six weeks after birth, blood samples were collected from the infants to determine thyroid function disorders, including transient hypothyroxinemia, neonatal hypothyroidism, transient primary neonatal hypothyroidism, and transient hyperthyrotropinemia. Results: In total, 126 infants with mean gestational age of 30.5±2.29 weeks and mean birth weight of 1246.90±193.58 g were enrolled in this study. Thyroid-stimulating hormone (TSH) level of <5 μU/mL was detected in 97 neonates. Transient hypothyroxinemia (low free T4 level, normal TSH) was the most frequent thyroid disorder detected in 42 infants (33.33%). Moreover, neonatal hypothyroidism, transient primary neonatal hypothyroidism, and transient hyperthyrotropinemia were observed in 8 (6.34%), 15 (11.90%), and 9 neonates (7.14%), respectively. Clinical events were similar between infants with and without thyroid dysfunction. In addition, incidence of clinical events had no difference between infants with any type of thyroid function disorders. Conclusion: According to the results of this study, thyroid function disorders are relatively common in preterm VLBW neonates, and serum T4 level is correlated with gestational age in these infants. Therefore, thyroid function tests with a consistent protocol are required for premature infants. It is recommended that further research be performed on larger sample sizes to investigate the prevalence of thyroid function disorders in preterm infants.