hyperthyroidism, hyperthyreosis, Graves’ disease
High level of T3 is excess of triiodothyronine (T3), one of two most important hormones produced by thyroid gland (Pic. 1), over the normal level that is 1,5 – 3 mmol/liter. The major form of thyroid hormone in the blood is thyroxine (T4), which has a longer half-life (time required for a quantity to reduce to half its initial amount) than T3. If an excess of circulating free thyroxine, free triiodothyronine, or both is occured, the condition is called hyperthyroidism. In a small subset of hyperthyroid patients only T3 is elevated (T3 toxicosis).
The function of the thyroid gland (Pic. 2) is one of the most important in the human body as it regulates majority of the body’s physiological actions. Any dysfunction in the thyroid can affect the production of thyroid hormones (T3 and T4) which can be linked to various pathologies throughout the body. Thyroid controls hormone production that helps the body regulate how it uses energy. A well-functioning thyroid gland is pivotal for a healthy body and to get pregnant, but also stay pregnant.
Thus, hyperthyroidism has a multi-system effect on the body, giving rise to a range of classic signs and symptoms (Pic. 3). Therefore it increases the consumption of energy of the body. Usually if a person is not pregnant or suffering from liver disease, a high level of T3 shows there might be issues with the thyroid gland.
Grave’s disease (an autoimmune disorder that directly affects the thyroid), being the most common cause of hyperthyroidism, accounts for 60-80% of all cases. Other causes include hyperthyroidism resulting from a toxic nodular goitre (single or multiple nodule) and these constitute the remaining 5-15% of all causes. Patients with Grave’s disease generally require a longer period of clinical management in order to achieve a state of normal thyroid level (euthyroidism) and this could explain infrequent periods in women and lower sperm counts in men, which can ultimately cause problems getting pregnant.
The level of T3 and T4 is measured in blood. Depending on the reason of increased T3 level, there is treatment for this condition. The management of hyperthyroidism is based on three treatment modalities, namely antithyroid medication, radioactive iodine ablation or surgery.
Hyperthyroidism must be distinguished from thyrotoxicosis, which is defined as the excess of circulating thyroid hormones in the bloodstream. Causes for thyrotoxicosis vary and include excess thyroid hormone ingestion, struma ovarii and functional metastatic thyroid carcinoma.
Patients present with nervousness, fatigue, palpitations, heat intolerance, polyphagia (excessive hunger) and weight loss. It is important to note that the elderly may present with a different range of symptoms and exhibit more subtle signs. Weight loss and anorexia are common symptoms in older patients and may be mistaken for the presence of a neoplastic process (cancerous growth) which can lead to over investigation.
The impaired function of thyroid gland may be associated with either the lower (hypothyroidisim) and higher levels of thyroid hormones (hyperthyroidism), such as T3. An undiagnosed thyroid disorder can make it difficult to conceive. It can also cause problems during pregnancy itself (pre-eclampsia, prematurity and congenital abnormality).
Grave’s disease is the most common cause of increased function of thyroid gland. Classically, it consists of a triad of hyperthyroidism with diffuse goiter (only symptom is swelling of the entire thyroid gland), different vision affection (ophthalmopathy; Pic. 3) and swelling around eyes (pretibial myxedema).
If left untreated, periods may be lighter and irregular periods and women may find it difficult to conceive. After treatment, a blood test to check thyroid condition is needed if women are planning to become pregnant. Using a contraceptive during and after treatment is recommended if women are not planning to get pregnant, as normal fertility can return extremely quickly.
Graves’ disease is associated with low pregnancy rate because thyrotoxicosis (excessive production of thyroid hormone) decreases the fertility rate. However in women with Graves’ disease who became pregnant, successful pregnancy outcome is low because Graves’ disease causes increased pregnancy loss and its complications.
Uncontrolled hyperthyroidism in pregnancy is associated with an increased risk of severe pre-eclampsia and up to a four-fold increased risk of low birth weight deliveries. Some of these unfavourable outcomes are more marked in women who are diagnosed for the first time in pregnancy.
Graves’ disease exacerbates during the first trimester of pregnancy and postpartum period, while it improves during the second and third trimester of pregnancy.
Patient with hyperthyroidism can suffer from a rapid heart rate, a heart rhythm disorder called atrial fibrillation and congestive heart failure (the heart is not able to pump sufficient amount of blood into body). The rapid and irregular heartbeat increases the risk of blood clot formation inside the heart. These clots may eventually become dislodged, causing embolism, stroke and other disorders.
Women who have been diagnosed with a heart condition should check with their physician to see if treatment and pregnancy are safe for them. In men, the association between heart diseases and abnormal sperm has been found.
Untreated hyperthyroidism can create brittle bones. High amount of thyroid hormones blocks incorporation of calcium into bones which then makes bones fragile and they are easily broken, causing pain and disability, which may decrease the desire for a child.
Sudden exacerbation (worseining) of symptoms is called thyroid storm, also known as thyrotoxic crisis. Such a crisis presents with fever, abdominal pain, vomiting, diarrhea, psychosis, altered mental state and coma. Thyroid storm is especially common in women who receive low or no prenatal care and those who have medical or obsteric complications. Therefore, pregnant women with hyperthyroidism require careful management to prevent complications and adverse outcomes for both her and her child.
Normal thyroid function is essential for normal function of the gonadal axis (control system that refers to the hypothalamus, pituitary gland, and gonadal glands; Pic. 4), thus important in maintaining normal reproductive capacity. On the contrary, any type of thyroid dysfunction may reduce the likelihood of pregnancy; the later can be restored to normal after appropriate treatment.
Thyroid diseases are very common in women of reproductive age. Infertility incidence is about 5-8% in women with hyperthyroidism. Previously menstrual disorders including particularly oligomenorrhea (infrequent menstruation) has been reported as 50% in people with hyperthyroidism. Hyperthyroidism may interfere with the mechanisms of ovulation and with sex hormone metabolism. If ovulation does not occur, the natural fertilization is not possible. If pregnancy does occur, the incidence of early pregnancy losses is increased and negatively affects fetal health.
With a proper treatment, the symptoms of hyperthyroidism including irregular periods are often cured.
Male fertility can be affected by a hyperthyroidism as well. It causes erectile dysfunction, delayed or premature ejaculation and low sex drive. Also, high thyroid levels can lead to higher than normal testosterone level and gonadotropin hormones. Steroid hormones, such as testosterone, are necessary for the development and maintenance of secondary sexual characteristics (features that appear during puberty) as well as initiation and maintenance of sperm development (spermatogenesis). Althought testosterone is required in large local concentrations to maintain the process, high testosterone levels in men may also lower the overall production of sperm. A failure spermatogenesis is a common cause of male infertility because a presence of abnormal sperm. The diagnosis of abnormal sperm does not mean infertility, but fertilization may take longer time. If natural conception does not work, there is always the option of in vitro fertilization (IVF).
Hyperthyroidism is generally treatable with no long-term adverse effects and only rarely is life threatening. In most cases, the problem causing hyperthyroidism can be cured, or the symptoms can be eliminated or greatly reduced.
Getting thyroid disease under control will usually reverse the fertility issues automatically. Mean radioactive iodine (370 MBq) dose used in treating hyperthyroidism is curative and it doesn’t affect gonadal performance. Still, because of teratogenic safety not to become pregnant for 6 months is recommended. Also, before planning a pregnancy be sure that hypothyroidism is not present.