Pregnancy thyroid hormones

The effects of deficiency are most pronounced pre- and perinatally due to the rapid rate of growth and the nutritional demands of the embryo and fetus. In the first half of pregnancy thyroid hormones are suppfied to the fetus by the dam. Later in the pregnancy the fetal thyroid is able to produce thyroid hormones (Nathanielsz, 1976), but is... 

These drugs are used cautiously in patients with Addison s disease and during lactation. The thyroid hormones are classified as Pregnancy Category A and are considered safe to use during pregnancy. 

Hyperthyroid effects In rare instances, the administration of thyroid hormone may precipitate a hyperthyroid state or may aggravate existing hyperthyroidism. Pregnancy Category A. 

Hypothyroid women frequently have anovulatory cycles and are therefore relatively infertile until restoration of the euthyroid state. This has led to the widespread use of thyroid hormone for infertility, although there is no evidence for its usefulness in infertile euthyroid patients. In a pregnant hypothyroid patient receiving thyroxine, it is extremely important that the daily dose of thyroxine be adequate because early development of the fetal brain depends on maternal thyroxine. In many hypothyroid patients, an increase in the thyroxine dose (about 30-50%) is required to normalize the serum TSH level during pregnancy. Because of the elevated maternal TBG levels and, therefore, elevated total T4 levels, adequate maternal thyroxine dosages warrant maintenance of TSH between 0.5 and 3.0 mll/L and the total T4 at or above the upper range of normal. 

The transplacental passage of maternal iodothyronines is quantitatively modest, although it might be sufficient to ensure adequate fetal development. Maternal thyroid hormone secretion is markedly increased during pregnancy (by 25-50%) thyroid therapy should therefore be carefully adjusted during pregnancy (58). 

Increasing use of Sephadex G-types, LH-20 and Bio-Gel P types for adsorption chromatography has been made. For example a number of methods have been reported for the determination of oestrogens, from pregnancy urine on G-15 [197] and from plasma on LH-20 [198]. Xanthurenic acid in urine has been determined using a procedure based on adsorption to Sephadex [199] and serum uric acid has been purified by adsorption to Bio-Gel P-2 [200]. The binding of thyroid hormones to Sephadex is well known [201] and forms the basis of a number of thyroid function tests [202, 203]. A number of kits based on Sephadex are commercially available and some of these kits were recently compared [204],... 

B Of the thioamides PTU is less likely to cross the placenta compared with methimazole and is the pr erred agent in pregnancy. PTU is also preferred over methimazole because it deaeases the peripheral conversion of Tt to Tj, whereas methimazole does so minimally. Both thioamides are used before surgery to decrease thyroid hormone stores and prevent intraoperative complications. PTU is routinely used during thyroid storm and not myxedema coma. 

The 24-hour RAIU wiU be suppressed to less than 2% during the thyrotoxic phase of painless thyroiditis. Antithyroglobuhn and antimicrosomal antibody levels are elevated in more than 50% of patients. Painless thyroiditis frequently occurs during the immediate postpartum period, and individual patients may experience recurrence of the disease with subsequent pregnancies. Patients with mild hyperthyroidism and painless thyroiditis should be reassured that they have a self-hmited disease. Adrenergic symptoms may be ameliorated with propranolol. Antithyroid drugs are not indicated because they do not decrease the release of preformed thyroid hormone. 

Table 1 Thyroid hormone and binding protein results in pregnancy...

DEGRADATION AND EXCRETION T, is eliminated from the body with a tj of 6-8 days. In hyperthyroidism, the tj is shortened to 3 or 4 days in hypothyroidism, it may be 9-10 days. These differing half-lives presumably reflect altered rates of hormone metabohsm. In conditions associated with increased binding to TBG, such as pregnancy, clearance is retarded. The opposite effect is observed when there is reduced TBG or when certain drugs inhibit thyroid hormone binding (Table 56-1). T, which is less avidly bound to protein, has a tj of 1 day. 

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