Thyroid Hormone Concentrations in Preterm Infants

Moon, Sung Keun; Kim, Jeong Nyun; Park, Mi Jung; Choi, Myung Jae; Chung, Chrul Young

Abstract

PURPOSE: To establish reference ranges for thyroid hormone concentrations in premature infants, we measured T4 and thyroid stimulating hormone (TSH) concentrations and analyzed the relation to gestational age and birth weight.
METHODS
Serum T4 and TSH concentrations were measured by radioimmunoassay for 391 premature infants born in Sanggye Paik Hospital for two years and eight months.
RESULTS
Gestational age of the subjects was 33.3 +/- 2.4 weeks (range : 26-37 weeks). Birth weight was 2,016 +/- 520g (range : 880-3,510g). Sampling date was 10.5 +/- 8.6 day (median value 8 day). Serum T4 concentrations for the gestational age 26 to 28, 29 to 31, 32 to 34 and 35 to 37 week groups were 4.8 +/- 3.6, 5.6 +/- 3.6, 6.4 +/- 4.4 and 7.0 +/- 4.6 microgram/dl, respectively. Serum T4 concentrations for the birth weight below 1,500, 1,500 to 1,999, 2,000 to 2,499 and above 2,500g groups were 5.7 +/- 3.8, 5.8 +/- 3.6, 6.4 +/- 4.6 and 8.1 +/- 5.1 microgram/dl, respectively. Serum TSH concentrations for the gestational age 26 to 28, 29 to 31, 32 to 34 and 35-37 week groups were 6.5 +/- 3.0, 7.2 +/- 6.1, 5.8 +/- 5.0 and 5.6 +/- 5.1 mIU/ml, respectively. Serum TSH concentrations (mean +/- SD) for the birth weight below 1,500, 1,500 to 1,999, 2,000 to 2,499, above 2,500g groups were 8.3 +/- 6.8, 5.7 +/- 4.3l, 5.5 +/- 5.1 and 5.6 +/- 5.2 mIU/ml, respectively. Serum T4 concentrations correlated positively with gestational age (y=0.31x-3.7, R2=0.03, P<0.05) and birth weight (y=0.001x+3.33, R2=0.33, P<0.05). Serum TSH concentrations correlated negatively with gestational age (y=-0.25x+16.1, R2=0.01) and birth weight (y= -0.001x+10.6, R2=0.01).
CONCLUSION
Serum T4 concentration in premature infants positively correlated with gestational age and birth weight. Transient elevation of serum TSH concentration was normalized at follow- up test. We recommend that a reference value should be set according to gestational age and birth weight.