Pregnancy maternal thyroxine

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. 

IODINE DEHOENCY, MATERNAL THYROXINE LEVELS IN PREGNANCY AND DEVELOPMENTAL DISORDERS IN THE CHILDREN... 

There is a spectrum of Impairment ranging from death through clinical endemic cretinism and subclinical deficits of motor and cognitive performance, to normality. This spectrum of effects appears to be associated with maternal thyroxine during pregnancy. No association with maternal triiodothyronine was found. 

Further data from Papua New Guinea indicates a relationship between the level of maternal thyroxine with the outcome of current and recent past pregnancies including mortality and the occurrence of cretinism. There were proportionally more perinatal (i.e., stillbirths and neonatal) deaths, and cretins, among the offspring of women who showed the lowest levels of serum thyroxine ... 

These data, indicating the importance of maternal thyroid function to fetal survival and development, are complemented by extensive animal data. Recent findings from the study of experimental animal models and more recently in man, indicate that there is a transfer of maternal thyroxine early in pregnancy. It would seem likely therefore that the effects of iodine deficiency on the fetus are... 

The fetus is totally dependent on maternal iodine supply throughout gestation, and on thyroxine supply during the first trimester of pregnancy for normal neurological development and nervous system maturation. It is therefore imperative that TH synthesis is adequate and is met with the appropriate iodine intake. Accordingly, it is important to know the trimester-specific reference intervals for THs and other thyroid functions in pregnancy. 

Hypothyroxinemia is a condition characterized by normal TSH concentrations but maternal free-thyroxine concentrations that are below the normal range for the stage of pregnancy. 

Figure 108.1 Human fetal and neonatal hypothyroid syndromes iodine defioienoy and endemic cretinism. If environmental iodine deoreases, maternal iodine deficiency in early pregnancy will not provide the fetal thyroxine required for neural development. Insuffioient supply of iodine leads to fetal and neonatal hypothyroidism.

The first 3 cases (serial nos 604, 638, 515) in the table had hormonal profiles entirely consistent with severe hypothyroidism although these women did not exhibit the clinical features of hypothyroidism In all three cases the pregnancy outcome was a stillblrth/early neonatal death In the succeeding 3 cases (serial nos 568, 245, 430) the maternal total and free thyroxine values were low but triiodothyronine values were within the normal range In one of these the outcome was a stillbirth/early neonatal death and one child has a hearing/speech defect but no other abnormality and, by our definition, cannot be labelled as an endemic cretin ... 

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