Serum iodothyronines in the human fetus and the newborn: Evidence for an important role of placenta in fetal thyroid hormone homeostasis

Ferruccio Santini, Luca Chiovato, Paolo Ghirri, Paola Lapi, Claudia Mammoli, Lucia Montanelli, Giovanna Scartabelli, Giovanni Ceccarini, Luca Coccoli, Inder J. Chopra, Antonio Boldrini, Aldo Pinchera

Research output: Contribution to journalArticlepeer-review


The pattern of circulating iodothyronines in the fetus differs from that in the adult, being characterized by low levels of serum T3. In this study, concentrations of various iodothyronines were measured in sera from neonates of various postconceptional age (PA). Results obtained in cord sera at birth (PA, 24-40 weeks), reflecting the fetal pattern, were compared with those found during extrauterine life in newborns of 5 days or more of postnatal life (PA, 27-46 weeks). The main findings are: Starting at 30 weeks of PA, serum levels increase linearly during extrauterine life; and at 40 weeks, they are more than 200% of those measured in cord sera from newborns of equivalent PA. Serum reverse T(s) (rT3) levels during fetal life are higher than these measured during extrauterine life; but they significantly decrease, starting at 30 weeks of PA. Serum T(3) sulfate (T3S) does not significantly differ between the two groups, showing the highest values at 28-30 weeks of PA, and significantly decreasing at 30-40 weeks. T3S levels are directly correlated with rT3, both in fetal and extrauterine life, whereas a significant negative correlation between T3S and T3 is found only during extrauterine life. In conclusion: 1) changes in serum concentrations of iodothyronines in umbilical cord and during postnatal life indicate that maturation of extrathyroidal type I-iodothyronine monodeiodinase (MD) accelerates, starting at 30 weeks of PA; 2) high levels of type III-MD activity in fetal tissues prevent the rise of serum T3, whereas they maintain high levels of rT3 during intrauterine life; 3) an important mechanism leading to the transition from the fetal to the postnatal thyroid hormone balance is a sudden decrease in type III-MD activity; iv) because placenta contains a high amount of type III-MD, it is conceivable that placenta contributes to maintain low T3 and high rT3 serum concentrations during fetal life and that its removal at birth is responsible for most changes in iodothyronine metabolism occurring afterwards.

Original languageEnglish
Pages (from-to)493-498
Number of pages6
JournalJournal of Clinical Endocrinology and Metabolism
Issue number2
Publication statusPublished - 1999

ASJC Scopus subject areas

  • Biochemistry
  • Endocrinology, Diabetes and Metabolism


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