Thyroid Function in Very Low Birth Weight Infants: Effect of Neonatal Disease, Chronic Lung Disease, Iodine and Dopamine

Abstract 502

Objective: To study the impact of neonatal disease, gestational age and pharmacological influences on thyroid function in VLBW-infants in the 3^rd and 6-7^th week of age. Method: Analysis of three Thyroxine (fT4) and Thyroid stimulating hormone (TSH) - values obtained on day 14-21 and 35-49 in 92 VLBW-infants. Data were correlated to birth weight, gestational age, intrauterine growth retardation, occurrence of perinatal asphyxia and/or intracranial hemorrhage, neonatal bacterial infection, chronic lung disease, treatment with dopamine and intravenous application of iodine-containing contrast medium. Data of infants with complex dysmorphology, cyanotic cardiac defects, thyroxine-treatment or death before 6 weeks of age were excluded. Results: Free T4 ranged between 0.6 and 1.8 ng/dl in the total group (Median 1.1 ng/dl) and was positively correlated to gestational age. TSH levels varied widely (0.13 - 11.11 mU/L). No infant had primary hypothyroidism. Free T4 -levels determined in the 3^rd and 6-7^th week were significantly decreased in neonatal disease and were lowest in chronic lung disease (table). Dopamine treatment did not reduce TSH-release. Intravenous application of iodine-containing contrast medium during the first two weeks of age did not result in impaired thyroid function at 3 and 6-7 weeks of age. Conclusion: In VLBW-infants thyroid function is not only positively correlated to gestational age but in addition altered due to neonatal disease and may therefore lead to an increased risk of hypothyroxinemia and consecutively impaired neurological development. Administration of dopamine (≥5µg/kg/min) or iodine-containing contrast media (total dose equivalent to 60-300 mg iodine) did not affect thyroid function in our study. Future studies on the beneficial effects of thyroxine administration should focus on infants of < 28 wks. gestational age and chronic lung disease. In our study these infants had lowest free T4-values until 6-7 weeks of age.

Table 1 Effect of neonatal disease (CLD: Chronic lung disease; IVH: Intraventricular hemmorrhage) on free T4 (fT4) - levels in VLBW-preterms at 3 and 6-7 weeks of age. Values are Median/Range; *p < 0.05, **p < 0.01.