Hypothyroidism_pregnancy_Elnashar

Hypothyroidism_pregnancy_Elnashar - Prof. Aboubakr Elnashar...

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Prof. Aboubakr Elnashar
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Control of thyroid function by a negative-feedback loop: The hypothalamus releases TRH TRH acts on the pituitary gland to release TSH TSH acts on the thyroid gland to release the thyroid hormones (T 3 and T 4 ) that regulate metabolism TRH and TSH concentrations are inversely related to T 3 and T 4 concentrations. 99% circulating T 3 and T 4 is bound to TBG. 1% circulate in the free form, and only the free forms are biologically active.
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Physiological changes of thyroid during pregnancy 1.TBG Increase {hepatic synthesis is increased} 2. TT4 & TT3 increase to compensate for this rise 3. FT4 & FT3 decrease. FT4 are altered less by pregnancy, but do fall a little in the 2 nd & 3 rd trimesters. 4. TSH decrease in 1 st trimester, between 8 & 14 ws {increase HCG, HCG has thyrotropin-like activity}, increase in 2 nd & 3 rd trimester {Increased
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5 . Pregnancy is associated with a state of relative iodine deficiency {a. increase maternal iodine requirement because of active transport to fetoplacental unit b. Increase iodine excretion in urine, 2 fold, because of increased GFT & decreased renal tubular reabsorption} The thyroid gland increases its uptake from the blood 3 fold {fall of plasma iodine} If there is already dietary insufficiency of iodine, the thyroid gland hypertrophies in order to trap a sufficient amount of iodine
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Non-pregnant 1st trimester 2nd trimester 3rd trimester TSH mu/l 0-4 0-1.6 0.1-1.8 0.7-7.3 FT4 pmol/ l 11-23 11-22 11-19 7-15 FT3 pmol/ l 4-9 4-8 4-7 3-5 The shaded area represents the normal range in non pregnant
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Thyroid physiology and the impact of
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Fetal thyroid function During early gestation: the fetus receives thyroid hormone from the mother. Maternal T 4 crosses the placenta actively, the only hormone that does so. (T3, TSH)
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Hypothyroidism_pregnancy_Elnashar - Prof. Aboubakr Elnashar...

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