Fetal thyroid function.

Area of Science:

• Endocrinology
• Fetal Medicine
• Neonatology

Background:

• Cordocentesis enables in utero assessment of fetal thyroid function.
• Fetal thyroid hormone levels and binding globulin concentrations change throughout gestation.
• Maternal thyrotropin-releasing hormone (TRH) can stimulate fetal thyroid-stimulating hormone (TSH) production.

Purpose of the Study:

• To investigate the maturation and regulation of fetal thyroid function during intrauterine life.
• To assess the fetal pituitary-adrenal axis response to exogenous TRH.
• To examine thyroid hormone status in small-for-gestational-age fetuses.

Main Methods:

• Analysis of fetal TSH, thyroxine (TT4, FT4), and triiodothyronine (TT3, FT3) concentrations via cordocentesis.
• Administration of maternal TRH from 25 weeks gestation to evaluate fetal TSH response.
• Comparison of thyroid hormone levels between normal and small-for-gestational-age fetuses.

Main Results:

• Fetal TSH, TBG, TT4, and FT4 increase progressively, reaching adult levels at term or 36 weeks gestation.
• Fetal pituitary-adrenal axis responds robustly and rapidly to maternal TRH, independent of gestational age.
• Small-for-gestational-age fetuses exhibit elevated TSH and reduced TT4/FT4, correlated with hypoxemia and acidemia.

Conclusions:

• Fetal pituitary, thyroid, and liver maturation appear independent and autonomous in utero.
• The fetal pituitary demonstrates heightened sensitivity to TRH compared to adults.
• Altered thyroid hormone levels in compromised fetuses may impact brain development and oxygen requirements.