Objective: Congenital hypothyroidism (CH) with delayed thyroid-stimulating hormone (TSH) elevation is a common form of thyroid dysfunction among premature infants. Routine newborn screening (NBS) may miss infants with CH with delayed TSH elevation. The objective of the study is to determine the prevalence of CH with delayed TSH elevation in premature infants and to identify associated risk factors.
Study design: Retrospective analysis of serum thyroid function screening (TFS) at day of life 30 in premature infants <30 weeks gestation, admitted to University of Iowa Neonatal Intensive Care Unit between 1 July 2012 to 30 June 2015. Serum free thyroxine and TSH levels were obtained in premature infants <30 weeks gestation on day of life 30. Follow-up testing and pediatric endocrinology consultation were done according to the institutional protocol.
Result: In total, 286 infants were included. All infants underwent routine NBS and 280 patients underwent TFS. Twenty-six patients (9.1%) were diagnosed with thyroid dysfunction. NBS identified only three patients. CH with delayed TSH elevation was diagnosed in 20 patients (6.9%) and was significantly associated with multiple gestation, lower birth weight, higher gestational age and lower 5 min APGAR score.
Conclusion: Thyroid dysfunction is common among premature infants born before 30 weeks gestation. The majority of cases with thyroid dysfunction had CH with delayed TSH elevation, which was not detected by NBS. We recommend measurement of serum TSH and free T4 levels on day of life 30 in premature infants born at <30 weeks gestation to identify patients with CH with delayed TSH elevation.