ESPE Abstracts

Background: It is often difficult to establish whether hyperthyrotropinemia in preterm newborn is a simple physiologic energy sparing phenomenon or a true hypothyroidism requiring replacement treatment.

Objective and hypotheses: This study aimed to find in what extent thyroid function in the preterm newborn can be influenced by clinical characteristics and complications.

Method: We studied 35 preterm newborn, gestational age (GA) 32.0 (2.1) weeks, 21 males, 13 small for gestational age (SGA), positive at TSH neonatal screening and with persistent hyperthyrotropinemia during hospitalization. We collected the following clinical data: GA, type of delivery, birth weight (BW), length (BL) and head circumference, clinical complications (RDS, jaundice, infections), time of detection and level of the pathologic TSH value in the dried blood spot (DBS) and in the serum sample, time of starting L-thyroxine and its dosage at steady state. Data are reported as median (IQR). Mann-Whitney test and simple regression were applied for statistical analysis.

Results: TSH levels and time of detection of pathologic values were not correlated to GA, BW, length and head circumference. SGA showed lower serum TSH levels (14.6 (5.1) μU/ml vs 22.6 (69.9) μU/ml; P<0.05). The patients with RDS showed lower TSH levels compared with patients without RDS (14.6 (7.9) μU/ml vs 24.0 (66) μU/ml; P<0.05) and required lower L-Thyroxine dosage at steady state (6.6 (4.0) vs 10.0 (2.0) μg/kg per day; P<0.05). The starting time of replacement treatment was inversely correlated to BW and BL (P<0.05) but was not different in SGA compared to appropriate for gestational age newborns. The patients who received replacement treatment had significantly higher pretreatment TSH in serum (18.11 (65.07) μU/ml vs 11.55 (10.83) μU/ml; P<0.02) but not in DBS (10.0 (23.75) μU/ml vs 6.69 (3.05) μU/ml; P>0.05).

Conclusion: Our results support the hypothesis that subclinical hypothyroidism could play a protective effect on growth and respiratory function in the preterm newborn. Further studies are needed to determine whether or not to undertake replacing therapy.