Factors Affecting Thyroid Hormone Changes Over 1 Month After Birth in Preterm Newborns

• Published in: Journal of the Endocrine Society Vol. 5; no. Supplement_1; p. A714
• Main Authors: Kim, Seulki, Kim, Sung Eon, Lee, Na Yeong, Ahn, Moon Bae, Kim, Shin Hee, Cho, Won Kyung, Cho, Kyung Soon, Jung, Min Ho, Suh, Byung-Kyu
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 03.05.2021
• Subjects: Pediatric Endocrinology
• ISSN: 2472-1972; 2472-1972
• DOI: 10.1210/jendso/bvab048.1453

Abstract Purpose: To analyze factors affecting thyroid hormone changes over 1 month after birth in preterm newborns. Methods: Thyroid hormones, including free thyroxine (fT4) and thyroid stimulating hormone (TSH) of 216 preterm newborns (mean gestational age [GA] 33.6±2.6 weeks), were retrospectively reviewed at the 1st and 4th weeks after birth. Preterm newborns were classified into three groups according to the GA (< 28 weeks, group A; 28-32 weeks, group B; 32-36 weeks, group C). The association between thyroid hormone changes and clinical factors was analyzed. Results: Preterm newborns with older GA had higher concentrations of fT4 (group A, 0.9±0.2 ng/dL; group B, 1.2±0.2 ng/dL; group C, 1.5±0.3 ng/dL) and TSH (group A, 2.7±3.2 mIU/L; group B, 4.5±3.3 mIU/L; group C, 6.0±3.8 mIU/L), both at the 1st week after birth. fT4 and TSH at the 1st week after birth were positively correlated with the GA (r=0.52, P=0.0001; r=0.30, P=0.0001) and Apgar score at 5 minutes (r=0.31, P=0.0001; r=0.28, P=0.0001). TSH concentration at the 1st week after birth was significantly lower in the abnormal brain sonogram group than in the normal brain sonogram group (4.4±3.7 vs 6.1±3.4 mIU/L, P=0.001); there were no differences at the 4th week after birth between these groups (4.2±2.6 vs 3.4±2.4 mIU/L, P=0.485). Multiple linear regression analysis revealed that GA was positively correlated with fT4 and TSH at the 1st week, and fT4 at 4th week after birth (B=0.08, SE=0.12, P=0.0001; B=0.34, SE=0.15, P=0.029; B=0.02, SE=0.01, P=0.013). Conclusion: Thyroid hormone levels in preterm newborns are mostly within the normal reference value of full-term newborns within 4 weeks of life, and are mainly affected by GA and brain ultrasound abnormalities.