Hypothyroidism triiodothyronine T3 and thyroxine T4

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Pregnant women with hypothyroidism have a higher risk of complications {Glinoer 1997), and hypothyroidism during pregnancy can impair the mental development of the child. In particular in relation to iodine deficiency, this has been understood for a long time.

According to a recent study on 60 hypothyroid women (whose disease was only diagnosed after 12 weeks of pregnancy), hypothyroidism impaired the mental and motor capacities of their children, who were tested at the age of 2 years compared to children of euthyroid or only discrete hypothyroid women during pregnancy (Pop 2003). Haddow (1999) draws similar conclusions from his study on 60 children aged 7-9 years. Their mothers only suffered from discrete hypothyroidism during pregnancy. Based on these results, hypofunction of the thyroid should be diagnosed and treated for the benefit of Lhe developing unborn child. Regarding the risk of neonatal hypothyroidism after maternal thyrostatic therapy during pregnancy, sec section 2.15.7.

Pharmacology and toxicology

Hormonally effective thyroid hormones are the L-forms of triiodothyronine (T3) and thyroxine (T4), which are only metaboli-cally active in a free, non-protein-bound form. T3 is the biologically effective hormone with a short period of effectiveness, while T4 is a less effective prohormone or hormone depot that is deiodinated as needed to T3. Thyroid hormones are necessary for placental development. Placental transfer of thyroid hormones is limited (Burrow 1994). However, in the case of fetal thyroid agenesis, there is substantial transfer of maternal thyroxine because of the high concentration gradient.

L-thyroxine and liothyronine (T3) are available as medications. Correction of maternal thyroid deficiency with these medications is not associated with abnormal fetal outcome. The requirement for thyroid hormones increases during pregnancy. Therefore, hypothyroid women should increase their levothyroxinc dose. Thereafter, serum thyrotropin levels should bo monitored (Alexander 2004).

Recommendation. When thyroid hormones are indicated, thyroxine preparations should be prescribed because the mother retains control over the actual hormonal activity due to the conversion to triiodothyronine. Iodine should be supplemented as necessary. As soon as pregnancy is confirmed, women with hypothyroidism should increase their levothyroxine dose by approximately 30%. A simple rule is to increase the dose by 25-50 |ig at the beginning of pregnancy. During the second trimester a further dose increase is necessary, to an approximately 40-50% higher dose compared to the prepregnancy situation. Serum thyrotropin levels should be monitored in order to find the correct individual thyroxine dose. During thyrostatic therapy, thyroid hormones should not be given in addition because the need for placenta-permeable thyrostatics is increased as a result.

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Pregnancy And Childbirth

Pregnancy And Childbirth

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