Endocrine Disorders

Thyroid disorders

What are thyroid disorders?

The thyroid is a gland in the front of your neck that is part of the endocrine system, which controls the hormones in your body. Thyroid hormones help regulate the body’s overall metabolism and have a wide-ranging influence on weight, sleep, heart rate, blood pressure, exercise capacity, bowel regulation, and overall energy levels. Thyroid disorders are also the most common endocrine problems in women. Hyperthyroidism is an overactive thyroid (when it produces too much thyroid hormone). Hypothyroidism is an underactive thyroid (when it does not produce enough). Hypothyroidism is more common than hyperthyroidism.

Left untreated, thyroid issues can lead to infertility or miscarriages.

What causes thyroid disorders?

Problems with the thyroid can be caused by:

• iodine deficiency
• autoimmune diseases, in which the immune system attacks the thyroid, leading either to hyperthyroidism (caused by Graves’ disease) or hypothyroidism (caused by Hashimoto's disease)
• inflammation (which may or may not cause pain), caused by a virus or bacteria
• nodules, or non-cancerous lumps
• cancerous tumours
• certain medical treatments, including radiation therapy, thyroid surgery, and some medicines
• some genetic disorders

How do thyroid disorders affect fertility?

Hypothyroidism and low thyroid hormone levels can affect menstruation causing:

• very light or very heavy menstrual periods,
• irregular menstrual periods,
• or absent menstrual periods (a condition called amenorrhea).

An overactive or underactive thyroid may also affect ovulation (the release of an egg for fertilization). Thyroid disorders may prevent ovulation from occurring at all. Severe hypothyroidism can cause milk production – called hyperprolactinemia - in the breast while preventing ovulation.

Hypothyroidism can also cause a shortened second half of the menstrual cycle. This may not allow a fertilized egg enough time to attach to the womb. It can also cause low basal body temperature, high thyroid peroxidase (TPO) antibodies, and ovarian cysts, which can lead to pregnancy loss or an inability to become pregnant.

Diagnosing thyroid disorders during infertility treatment

Our first step in diagnosing thyroid disorders is to order a blood test that measures thyroid stimulating hormone (TSH). If the TSH level is too high, it may indicate that you have an underactive thyroid or hypothyroidism. If it is too low, it may mean that you have hyperthyroidism -i.e. an overactive thyroid. Typically, the normal range for TSH is 0.3 to 4.0, but your fertility specialist will evaluate these ranges, based on your symptoms.

When the TSH blood test produces abnormal results, this test may be followed up by a full thyroid panel, which evaluates levels of thyroxine (T3 and T4), as well as checks for thyroid antibodies.

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What is the treatment for thyroid disorders?

Hypothyroidism is usually treated with thyroid replacement therapy. This is achieved with medication that supplies and regulates the thyroid that the body is not currently producing in the correct amount.

Hyperthyroidism is also treated with medications, to decrease the production of the thyroid hormone, which is being produced in excess. The medications also inhibit the secretions of thyroxine (T3 and T4).