INTERNAL MEDICINE CENTER

Zion Women셲 Hospital, Serving with Love

The thyroid of a normal person is located right beneath the thyroid cartilage at the front of the neck and between the muscles going up the bronchus and ears. It is the size of a thumb and there is one on each side of the trachea, the sides connected into a band shaped like a butterfly. It is 5cm long, 2cm wide, and 2cm thick, with both sides and the connecting parts weighing a total of 15~20g.
The thyroid secretes thyroid hormones to maintain the function of all organs within the body. Hyperthyroidism or hypothyroidism may occur if there is too much or too little secretion of the hormones.
The thyroid is one of the largest endocrine organs. A sufficient amount of iodine must be ingested for thyroid hormones to be generated and the recommend daily requirement set by the WHO is generally 150ug/d and a minimum of 250ug/d for women who are pregnant or nursing, while the Korean Nutrition Society recommends 150ug/d for adults over 19, 240ug/d for women who are pregnant and 330ug/d for women who are nursing.
Thyroid diseases can be divided into functional abnormalities and morphological abnormalities and since pregnancy is particularly a 쐓tress test on the thyroid, attention must be paid to the thyroid conditions that may develop with the physiological changes accompanied with the pregnancy, the fetus demand of the thyroid hormones, and the delivery. Thyroid nodules occur quite frequently and are caused by various causes including thyroiditis, goiter, thyroid nodular hyperplasia, ganglion (cyst) and malignant tumors, the most common cause being thyroid nodular hyperplasia. Incidentalomas, which are lumps that are 1~1.5cm big and cannot be perceived by touch but found by chance through ultrasounds, are found 25~50% of the time in healthy adults and of those found, approximately 20~30% are malignant tumors. Thyroid cancer is a condition found in women and 10% of female cancer patients suffer from thyroid cancer.

The fetus does not have a functioning thyroid before 13~15 weeks of pregnancy. Therefore the woman셲 thyroid becomes larger with pregnancy to increase the production of thyroid hormones by up to 50% (20~40% increase in regions with insufficient iodine and 10% increase in region with abundant iodine). With the increased thyroid hormones and the effect of the chorionic gonadotropin secreted through the placenta, the normal range of thyroid hormones is recommended at 0.1~2.5mIU/L for the first 3 months of pregnancy and 0.2mIU/L, 0.3~2.5IU/L for the rest of the pregnancy.
The effect of the mother셲 thyroid hormones on the fetus growth and brain development is continued throughout the whole pregnancy. Replenishment of thyroid hormones is begun immediately for subclinical hypothyroidism that is detected after getting pregnant. Such replenishment can be discontinued when the pregnancy has been halted or after delivery and (if positive for anti-thyroid autoantibodies) is received 6~12 weeks after delivery for 6 months.
Hypothyroidism during pregnancy can cause infertility, miscarriage, gestational hypertension, anemia, placental abruption, preterm birth and postpartum hemorrhage for the mother , low birth weight, difficulty breathing when born, increase in perinatal morbidity and mortality for the fetus, and neuropsychiatric and cognitive abnormalities during infancy.
The high-risk group for thyroid disorders, which should be observed with caution, comprises age over 30, family history of thyroid conditions, goiter, anti-thyroid autoantibodies, symptoms of hypothyroidism, type 1 diabetes, autoimmune disease, infertility, miscarriage, preterm birth, radiation to the head and neck, previous experience of thyroid surgery, current intake of thyroid hormones and regions with insufficient iodine. Since there is also a high possibility that patients with type 1 diabetes or a chronic virus infection, who have recovered from Graves disease, or positive for anti-thyroid autoantibodies will develop thyroiditis after delivery, these patients are monitored after giving birth.

A temporary excess of thyroid hormones at the early stage of pregnancy does not require the administration of antithyroid agents but since hyperthyroidism (Graves disease) may be detected in the early stage of pregnancy or a previous hyperthyroidism may worsen, antithyroid agents are taken to maintain the upper limit of the mother셲 thyroid hormones (Free T4).
In many cases, pregnancy improves the condition of an autoimmune disease so that in the mid to final stages of pregnancy, only a small dosage of antithyroid agents is necessary since the Graves disease is alleviated and 20~30% can stop taking the medication. Nevertheless, the antithyroid agents must be maintained until the delivery if the titer of the TSH receptor antibodies has increased threefold of the normal upper limit. The Graves disease normally worsens after delivery.

沅곴툑븯떊 궡슜쓣 寃깋빐二쇱꽭슂!