Thyroid-stimulating hormone levels for boys and girls do not differ significantly during the first 2 years of life, although these levels are affected by different hormones for each sex, according to findings published in Thyroid.
“Thyroid hormones have a vital role in physical growth, differentiation and brain maturation during fetal and postnatal life,” Ioannis Legakis, MD, PhD, of the department of endocrinology and metabolism at Iaso General Hospital in Athens, Greece, and colleagues wrote. “Even though embryogenesis of the hypothalamus and pituitary and thyroid glands in the human fetus is largely completed by the 12th week of gestation, differentiation and functional maturation of the hypothalamus, pituitary and thyroid glands continue into the neonatal period.”
Legakis and colleagues measured TSH, triiodothyronine (free and total), thyroxine (free and total), antithyroid peroxidase and antithyroglobulin antibodies in 2,916 children (48.3% girls) born between 2015 and 2017 at Iaso General, Maternity and Gynecological Hospital in Athens, Greece. Measurements were taken every 5 days during the first month after birth. After the first month, during the first 2 years of life, the researchers spaced measurement collection by 5 months.
Boys in the cohort experienced a TSH decline from 7.03 µIU/mL at birth to 4.17 µIU/mL after 1 month and to 3.02 µIU/mL after 2 years. A similarly decreasing trend occurred in girls with measures of 5.26 µIU/mL, 3.92 µIU/mL and 2.96 µIU/mL at birth, 1 month and 2 years, respectively. The researchers noted no significant differences between boys and girls in median TSH. However, they found an association between free T4 and TSH in boys (P < .001) and between T3 and TSH in girls (P = .045). In addition, antithyroglobulin antibody levels had “much larger variability” for boys compared with girls, and a negative and “almost linear relationship” was observed between T3 and age after 5 months in all children, they wrote.
“Divergence observed in thyroid hormone maturation pattern between boys and girls in our longitudinal study might reflect differences in the maturation of the hypothalamicpituitarythyroid axis. In terms of clinical practice, our findings suggest a need for re-evaluating the reference ranges of thyroid parameters according to sex, especially in the first months of life and until the first year,” the researchers wrote. “Furthermore, our results suggest new optimal ranges for thyroid hormone replacement for that specific period.” – by Phil Neuffer
Disclosures: The authors report no relevant financial disclosures.