Age-specific correlation between thyroid hormone concentrations and ultrasound thyroid volume for diagnosing thyroid dysfunction in preterm infants: a single-centre, prospective, observational study protocol

INTRODUCTION: Thyroid disorders are commonly concomitant with premature birth; however, indications to start therapy remain unclear due to lack of gestational age-specific reference ranges and thyroid ultrasound nomograms. We aim to evaluate the age-specific correlation between circulating free thyroxine (FT4) and thyrotropin stimulating hormone (TSH) levels and ultrasound thyroid volume to assist identify infants requiring thyroid hormone replacement therapy. METHODS AND ANALYSIS: This is an observational, prospective, single-centre study that will include 200 preterm infants born between 24 and 32 weeks of gestational age, without any congenital diseases or malformation that may affect thyroid function. Venous blood will be obtained in infants at 14–21 days of life, and at 32 and 36 weeks of postconceptional age (PCA) to measure FT4 and TSH concentrations. Thyroid ultrasound will be performed at 32 and 36 weeks of PCA. Relevant outcomes will include determination of FT4 and TSH values and ultrasound thyroid volume for preterm infants born at 24–28 weeks of gestation and 29–32 weeks of gestation. Correlations among circulating hormone concentrations and thyroid volumes with the head circumference and body mass will also be determined. ETHICS AND DISSEMINATION: The Ethics Committee of the Medical University of Warsaw has approved the study protocol prior to recruitment (KB44/2019). Informed consent will be obtained from caretakers of preterm infants at the time of enrolment. Consent for participation in the study can be withdrawn at any time, without consequences and without obligation to justify the decision. All data will be stored in a secure, password-protected Excel file that is only accessible to researchers involved in the study. Findings will be published in a peer-reviewed journal and disseminated at relevant national and international conferences. TRIAL REGISTRATION NUMBER: NCT04208503.