Best Practice & Research Clinical Endocrinology & Metabolism
8Maternal thyroid hormones early in pregnancy and fetal brain development
Section snippets
Foreword: human rights
Every child has the right to an adequate supply of iodine to ensure his (or her) normal development.
Of particular importance in this context is the right of the unborn child.
‘Every mother has the right to an adequate iodine nutrition to ensure that her unborn child experiences normal mental development.’
These are Declarations emanating from the Convention on the Rights of the Child, United Nations Assembly, New York, 1989; World Summit for Children, United Nations, New York, 1990: Declaration
Thyroid hormones and their nuclear receptors in the human fetal brain
As already summarized, during most of the second half of the 20th century, the prevalent idea was that the early embryo and fetus actually developed in the absence of thyroid hormones. Supporting this conclusion was evidence of a placental ‘barrier’ system that limited drastically their transfer from the mother.27., 39., 40., 41. Recent information regarding the activity and expression of different iodothyronine deiodinases has confirmed the widespread distribution, mostly of D2 and D3, in the
The maternal surge of ft4 before mid-gestation
There is at present a widespread consensus that maternal hypothyroidism, both clinical and subclinical, requires early detection and prompt treatment, because of its significant negative effect for the woman, the pregnancy and her child. Confirmation of clinical and detection of subclinical hypothyroidism usually rely on an elevated maternal circulating TSH. Attainment of normal TSH levels is mostly used for follow-up during treatment, as is customary for non-pregnant women.86 This practice,
Summary
Contrasting hypotheses prevalent for most of the second half of the last century regarding the existence, or not, of the transfer of maternal thyroid hormones to the fetus and its possible relevance for neurodevelopment have now been largely reconciled: maternal thyroid hormones do reach the human fetus in biologically relevant amounts during the first trimester, enabling occupation of the nuclear receptors that are already expressed in the cerebral cortex. The high activities of several
Acknowledgements
We are grateful for the financial support of the Instituto de Salud Carlos III, RCMN (03/08) of Spain.
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