Hyperthyroidism during pregnancy

Pregnancy can lead to physiological changes in the thyroid gland, further affecting thyroid function test results. In the early stages of pregnancy, these results can lead to a report of hyperthyroidism, which is normal and does not require further treatment or correction. In contrast, pathologic hyperthyroidism does cause complications during pregnancy, such as miscarriage, preterm delivery, and further aggravation of the pregnant woman's heart burden, so further examination and evaluation and treatment are required.

Diagnosis of hyperthyroidism during pregnancy focuses on determining the cause and whether treatment is needed and which treatment should be chosen. The most commonly recommended treatment is the use of the anti-thyroid drug MMI (Lica^®) or PTU (Polupi^®), but it should be noted that MMI (Lica^®) will have teratogenicity during the first trimester of pregnancy. Therefore, PTU (Polupi^®) is recommended for the first stage of labor as follows:

The use of antithyroid drugs during pregnancy and fetal considerations

During pregnancy, both antithyroid drugs and TRAb will further affect the thyroid gland of the fetus through the placenta. In contrast, T3 and T4 will be affected by the high concentration of type 3 deiodinase in the placenta. Only a very small amount will reach the fetus through the placenta, meaning the inhibitory drugs taken and the stimulating antibodies in the mother will have an impact on the fetus after combined. However, the fetus cannot receive proper supplement of thyroid hormones from the mother, resulting in hypothyroidism and insufficient thyroid hormone production.

Therefore, once the thyroid gland of the fetus starts to function, the anti-thyroid drugs will further affect the thyroid gland of the fetus, making it less functional and subsequently causing compensatory gland enlargement. Therefore, the premise of treatment is to minimize the amount of anti-thyroid drugs used by the mother.

In the evaluation of treatment dose, because TSH will have a state of physiological inhibition, there are few indications in the evaluation of drug dose during pregnancy. In clinical practice, using free T4 to evaluate the treatment dose is recommended, so that the lowest dose of anti-thyroid drugs can be used during pregnancy. In general, it is advised to maintain the upper limit of free T4 a little higher.

Surgical treatment during pregnancy

Pregnancy is a relative contraindication to thyroidectomy, and surgery is usually considered only if the use of antithyroid drugs fails, and if surgery is still considered for treatment, it is recommended that it be performed during the second trimester. The main consideration is the possible teratogenicity of anesthetics in the first trimester and the risk of premature birth caused by surgery in the third trimester. It should be noted, however, that surgery in the second trimester is not entirely risk-free, as there are still 4.5 to 5.5 percent of preterm births.

The operation usually results in the gradual decrease of TRAb, but after the mother stops using the antithyroid drugs, the unreduced TRAb will still be transported from the mother to the fetus via the placenta. As mentioned before, TRAb will further stimulate the thyroid tissue of the fetus, resulting in the same condition of goiter and hyperthyroidism as adults. At this time, special attention should be paid to the cardiovascular and skeletal development of the fetus. In general, fetal ultrasound should be closely followed.