Jhulan Das Sharma
Southern Medical College, Bangladesh
Title: Do preterm neonates require thyroxine replacement?
Biography
Biography: Jhulan Das Sharma
Abstract
Abstract: Context: Debate still exists about the necessity of thyroxine replacement in hypothyroxinaemic preterm neonates. The dilemma is that delaying replacement will impair growth and development, especially neurological development while early replacement may have adverse metabolic effect resulting from increased oxygen consumption of preterm newborns suffering from hypoxia. Moreover once replacement is initiated, it may injudiciously be used for prolonged period. Background: Transient hypothyroxinaemia is the most common thyroid dysfunction in preterm postnatals, and is characterized by low sera levels of T4 and FT4. The aetiology is not clear, but may have been due to the withdrawal of maternal placental T4 transfer, expression of temporary HPT axis immaturity, or a nonthyroidal illness. The problem is reported to be present in majority of infants born at less than 30 weeks gestation and is associated with increases in perinatal mortality and morbidity as well as later neurodevelopmental deficits. Objectives: To compare thyroid function in preterm and term neonates and to observe whether preterm neonates with hypothyroxinaemia need thyroxine replacement at the earliest or the treatment may as well be started, with proper follow ups, at about 6 weeks. Methods: An observational study was done during the period of July 2008 to June 2010 in the neonatal and postnatal unit of the Chittagong Medical College Hospital.It focuses on comparison of thyroid function (FT4 and TSH) between preterm and term neonates aged average 7 days with all samples collected after 5 days of life, the time when postnatal TSH surge disappears. One hundred (100) preterm and 50 term infants were selected by convenient sampling. Preterm infants were stratified by postconceptional age. FT4 and TSH estimation were done by the 3rd generation two site chemiluminesent immunometric assay. Serum levels of FT4 and TSH of preterm infants were followed after 6th week (45-50 days) of their age and were compared with their 1st samples (5-11 days). Results: The FT4 level correlated positively with gestational age (p<0.0001, n=150, r=0.61) and differed significantly between adjacent gestational age groups (p=0.0001). No significant differences were found in TSH levels of such age groups of the preterms. TSH level correlated positively with gestational age in the 1st samples but in the 2nd samples significant negative correlation was observed suggesting HPT axis maturity. In preterm neonates subgroup analysis showed highly significant difference in FT4 and TSH levels between 1st and 2nd samples. Conclusion: In preterm infants born at <28 weeks’ gestation, it usually takes more than one month for FT4 levels to reach level equal to those of term infants. In this study, FT4 levels were found to increase in all infants who had initial hypothyroxinaemia and did not receive thyroxine supplementation during the first 6 weeks of postnatal life. This indicates that thyroxine supplementation should be considered if free T4 levels are persistently low after the first 6 weeks of birth. Further studies are needed before clinical application of this finding.