PURPOSE: To evaluate the influence of gestational age(GA) and disease on thyroid hormone concentration in preterm neonates(preterm), we measured thyroxine (T4) and thyroid stimulating hormone(TSH) concentrations and analyzed the relation to GA and diseases. Additionally, we calculated the reference ranges of T4 in preterm for future investigation. METHODS: Serum T4 and TSH were measured by radioimmunoassay for 107 preterm who admitted neonatal intensive care unit during 1994. We sampled from preterm on 5th day of life. We analysed the relationship of GA and birth weight with the levels of T4 and TSH, and prospectively compared them with each neonatal disease. RESULTS: Serum T4 concentration correlated positively with GA(r=0.62, P<0.001) and birth weight(r=0.29, P<0.01). After controlling GA, birth weight did not correlate to the levels of T4. But after controlling birth weight, GA had correlation with T4(r=0.58, P<0.001). In preterm less than 32 weeks of GA, there was no difference of T4 level between healthy and the diseased(respiratory distress syndrome, patent ductus arteriosus, sepsis, intraventricular hemorrhage, and cerebral palsy). Group of bronchopulmonary dysplasia had significant lower level of T4 compared control group(P<0.01). The reference range of T4 in GA 32-36 weeks is 5.56-15.58 microgdL (9.82+/-.40 microgdL). CONCLUSION: GA positively correlated with serum T4 in preterm, but not to TSH. The measurement of TSH level, using in most of the neonatal care unit as neonatal thyroid screening test, in Korea, is not an adequate test to diagnosis hypothyroidism early in preterm. We recommend serial follow up of TSH and T4 in preterm.
Birth Weight* ; Bronchopulmonary Dysplasia ; Diagnosis ; Ductus Arteriosus, Patent ; Gestational Age* ; Hemorrhage ; Humans ; Hypothyroidism ; Infant, Newborn ; Infant, Premature* ; Intensive Care, Neonatal ; Korea ; Mass Screening ; Parturition* ; Prospective Studies ; Radioimmunoassay ; Reference Values ; Sepsis ; Thyroid Gland* ; Thyroxine