Is It Necessary to Measure T4 In Screening of Congenital Hypothyroidism in Preterm Infants?

Introduction: Immaturity of hypothalamus-pituitary-thyroid axis in preterm infants causes the low level of thyroxin hormone and hypothyroxinemia of prematurity (HOP). In our country, Iran TSH that is measured by filter paper is the only laboratory test for screening of hypothyroidism and the missing of the HOP is concerning. This research was done to evaluate the rate of HOP. Material and Methods: This prospective-descriptive study was conducted in 2017 in our hospital. In the participants included preterm infants with gestational age ≤34 weeks or birth weights ≤2000 grams, measurement of TSH and T4 were done by blood sampling instead of filter paper and the values of thyroid function tests were analyzed. Results: low levels of T4 were observed ( 14.2% related to HOP and 10.3% belonged to hypothyroidism).In comparisons the values of T4 in both of sampling: in 24 cases (11.8%) persistent hypothyroxinemia ,26(12.8%) delayed hypothyroxinemia and in 29(14.2%) transient forms of hypothyroxinemia were detected. Conclusion: Our research resulted that the rate of HOP is remarkable and measurement of T4 in the screening of preterm infants is recommended.