Pregnancy and Thyroid Diseases

The second most frequent endocrinological disorder in women in the reproductive age are the disorders of the thyroid hormone.

Production and secretion of hormones in the thyroid gland are under the control of hormones called TRH, which are secreted by the hypothalamus in the brain, and TSH, which are secreted by the pituitary gland. 99% of thyroid hormones in circulation normally bind to proteins called TBG, albumin and prealbumin and only 1% is free and active. A sufficient amount of iodine must be taken so that the production of the thyroid hormone can take place in its normal course.  Number of free T3 and T4 hormones in circulation decrease during pregnancy due to the increase in the TBG protein which binds thyroid hormones. Furthermore, the increase in hCG, which is the pregnancy hormone, represses hyprophysis leading to an increase in the level of TSH in the 8th to 14th weeks of pregnancy. Moreover, an increase in the iodine concentration in the plasma as the fetus uses the iodine too. For this reasons, a daily iodine intake of 200 micrograms (which is normally 150 micrograms) is advised during pregnancy. Another change observed during pregnancy is an increase of 15% in the size of the thyroid gland.

The thyroid gland of the fetus starts taking iodine in after the 12th week of pregnancy and starts producing thyroid hormones after the 14th week of pregnancy. Levels of TSH, TBH and thyroid hormones start increasing after the 20th week of pregnancy and reaches to the level in adults in the 36th week of pregnancy.

Whereas the T3, T4 in mother’s blood circulation and the medications used in treatment pass to the fetus through the placenta during pregnancy, TSH does not. TSH and thyroid hormones increase in the baby just after birth but hormone levels return to normal 6 weeks later.

Hyperthyroidism

95% of hyperthyroidisms observed during pregnancy are affiliated with the Graves disease. Hyperthyroidism during pregnancy might lead to miscarriages, stillbirths, preterm birth, retarded development in the baby, preeclampsia and cardiac dysfunction in the mother. Therefore, it is quite important to take hyperthyroidism under control before pregnancy.

Hypothyroidis

Hypothyroidis is seen in 0,05% of pregnant women. The risks of miscarriage, preeclampsia, ablatio placentae, retarded development in the baby, prematurity, antenatal infant death and neurological disorders in the baby increase in patients with this disease.

Thyroid Scan During Pregnancy

The most significant periods in the brain development of the fetus are the first 3 months and the last 3 months of pregnancy and the period from birth to 2-3 years of age. Therefore, should thyroid functions be scanned in the pre-pregnancy period or during the first pregnancy examination? Whereas American Society of Clinical Endocrinologists suggests that a scan should be performed, gynecologists do not suggest a scan for the present as there are no studies showing that the scan prevents mental retardation in the children that are born. However, a scan should be performed on those having a thyroid disease history or in the case that there are complaints that imply thyroid diseases.