Transient hypothyroxinemia without elevated thyroid-stimulating hormone (TSH) levels is common in prematurity, especially in very-low-birth weight (VLBW) infants. The transient hypothyroxinemia of prematurity (THOP) has been seen as a “benign” condition. Infants were classified as THOP by low thyroxine (T4) value without elevated TSH value (<20 µIU/mL). Primary hypothyroidism (PH) defined by low thyroxine (T4) and elevated thyroid-stimulating hormone (TSH) levels. Both of them can be seen at premature infants.
Retrospectively we compared the premature infants born at ≤32 weeks who required thyroxine supplementation for THOP and hypothyroidism. 24 neonates required thyroxine supplementation for THOP and 18 neonates for PH were included the study between January 2008 and December 2010.
There were no statistically differences in respect to demographic and prenatal characteristics between two groups. There was mild positive correlation between free T3, free T4 levels and gestational age. Median starting time of thyroxine supplementation was 13 days in PH and 21 days in THOP group (p=0.014). There were no statistically differences between groups in respect to birth-weight, hospitalization time, sepsis, NEC, PDA, and RDS rates. Although the THOP group started the thyroxine supplementation late, median weight of the neonates at discharge were significantly higher in THOP group (1774 vs 2070 p=0,018). Weight gaining per day after the thyroxine supplementation was significantly higher than the days before supplementation started (p=0.001).
Infants who get enough calories but not satisfactory gaining weight should be screened for THOP and PH.