**4. Hyperthyroidism and pregnancy**

Hyperthyroidism is defined as an excessive production of thyroid hormones caused by immune or nonimmune thyroid disease. Hyperthyroidism is less common than hypothyroidism, but nevertheless, it represents a great challenge for the physician, pregnant woman and developing fetus. Specific knowledge is required by healthcare providers and a team approach is necessary to provide the best possible cares for pregnant women with GD. Caring physicians (gynecologists, endocrinologists, cardiologists) must be aware of the symptoms of thyrotoxicosis, often overlapping with the pregnancy itself and of specific changes of the thyroid hormones during pregnancy. Knowing the fact, that any pregnancy complicated with hyperthyroidism carries a greater risk for complications for both mother and developing fetus, proper diagnosis and treatment are necessary. Adequate decisions about when to start treatment and with what to start are required, following the ancient principle of *primium non nocere*. Although our therapeutic approaches didn't change very substantially during the last fifty years, our understanding of the pathophysiology, hormonal changes, immunology and obstetric outcomes have changed dramatically. We still have at our disposal only two types of antithyroid drugs (ATD) (see later in the text), which are the same that had been in use since the 1950's and still remain the cornerstone of treatment of GD in pregnancy. Rarely, other approaches are necessary, like surgery during the second trimester. Radioiodine ablation is absolutely contraindicated. Close monitoring of thyroid hormone levels and frequent adjustment of the dose are necessary to avoid both overdosage or subdosage of antithyroid drugs.

The reasons for thyrotoxicosis during pregnancy can be divided in such typical for all patients and such specific for the pregnancy. The common causes for thyrotoxicosis include: Graves' Disease, chronic thyroiditis, painless thyroiditis, subacute thyroiditis, toxic adenoma, multinodular goiter; excessive levothyroxine (LT4) intake and drug induced thyrotoxicosis caused by iodine, amiodarone, lithium. The causes of thyrotoxicosis specific for the pregnancy are: gestational transient thyrotoxicosis, multiple gestations, trophoblastic disease, hyperplacentosis, hyperreactio luteinalis [22]. Graves' Disease and gestational transient thyrotoxicosis (GTT) account for the majority of hyperthyroidism in pregnancy. Graves' Disease affects 0.2% of pregnant women [42]. Thyrotoxicosis during pregnancy could affect both pregnant woman and developing fetus. Hyperthyroidism may cause both maternal complications such as heart failure, eclampsia and thyroid storm and also higher incidence of abortion, preterm delivery, low-birth-weight infants and neonatal mortality [43]. Distinguishing between different causes of hyperthyroidism is relevant, because some of them, like GTT, are transient, lead to mild thyrotoxicosis and do not require treatment with antithyroid drugs and are not associated with adverse pregnancy outcomes [44]. The Endocrine Society recommends that screening for thyroid conditions in pregnancy is performed in women >30years, those with previous personal or family history of thyroid disease, women with issues with conception and existing autoimmune conditions [45].
