Serum thyroglobulin in newborns’ cord blood, in childhood and adolescence: a physiological indicator of thyroidal status

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Abstract
Serum thyroglobulin (Tg) was measured in the cord blood of 635 newborns and serum thyroxine (T4) reverse triiodothyronine (rT3), TSH and T3 were measured in about 200 of them. Cord Tg was detectable in all newborns with a mean + SE value (50 ± 1.3 ng/ml) higher than that found in the serum of adult subjects (n = 144; Tg = 13 ± 1.1; p < 0.0001). Cord Tg had a log-normal distribution. A low, but positive correlation was found between cord Tg and cord TSH (n = 242; r = 0.17; p < 0.05) but not with cord T4 or cord rT3. Gestational age was negatively correlated with cord Tg or cord rT3 (rs = − 0.97; p < 0.01; rs = 0.89; p < 0.02, respectively) while was positively correlated with cord T4 or cord TSH (rs = 0.85; p < 0.05; rs = 0.86; p < 0.01, respectively). Birth weight, maternal diabetes, induction of labor with Oxitocin, cesarian section and newborns’ illness showed no influence on cord Tg levels when considered alone, but decreased cord Tg levels were found in ill newborns delivered by cesarian section. On the contrary, increased cord Tg levels were present in cord blood of newborns who developed hypoglycemia soon after birth and in small for gestational age newborns. In 24 newborns studied daily for the first 6 days of life, serum Tg was always detectable with mean values not different from those found in the cord blood. A progressive decrease in serum Tg concentrations was found after birth during infancy, childhood and adolescence (rs = − 0.88; p < 0.001). Adolescents’ serum Tg levels were similar to those of the adult population.