Factors Affecting Metabolic Bone Disease of Prematurity: Is Hypothyroxinemia Included?

OBJECTIVES: The association between transient hypothyroxinemia of prematurity (THOP) and metabolic bone disease of prematurity (MBD) is not clearly known. We aimed to evaluate the effects of THOP and other risk factors on MBD in very low birth weight infants. METHODS: This study included infants born at <30 weeks gestational age and <1500 g birth weight who were hospitalized between July 2016 and December 2019. The following information was obtained from medical records: Demographic characteristics; clinical follow-up data; morbidities; initial thyroid function tests; and calcium (Ca), phosphorus (P), and alkaline phosphatase (ALP) levels at postnatal 4–6 weeks. Newborns with an ALP level >500 IU/L were diagnosed with MBD. Patients without MBD were defined as Group 1 and patients with MBD were defined as Group 2. RESULTS: Our study enrolled 145 infants who met the inclusion criteria. The incidences of MBD and THOP were 16.5% and 56.5%, respectively. Gestational age and birth weight were significantly lower in Group 2 than in Group 1. It was observed that these infants received total parenteral nutrition for a longer period of time and had a longer transition period to full enteral feeding. In addition, duration of non-invasive mechanical ventilation, duration of oxygen treatment, frequencies of moderate-severe bronchopulmonary dysplasia, and postnatal steroid use were found to be significantly higher in babies in Group 2 compared to babies in Group 1. There was no significant difference between the groups in terms of THOP. However, multivariate logistic regression analysis revealed no risk factors for the development of MBD. The presence of MBD and Ca, P, and ALP levels did not differ significantly between patients with and without THOP. CONCLUSION: Our study reveals that MBD is a multifactorial disease and THOP is not a risk factor for the development of MBD.