Reproduction and the Thyroid

The thyroid is an important gland that influences metabolism, growth, development and body temperature as well as reproduction. Normal thyroid function is vital to fertility and reproduction.

Thyroid Gland Function

This small butterfly-shaped gland is located in the lower front of the neck. The main function of the gland is to take in iodine and convert it into the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones are released into the blood stream and work throughout the body to regulate metabolism.

The thyroid is regulated by the pituitary gland. When T3 and T4 levels drop, it stimulates the pituitary gland to produce Thyroid Stimulating Hormone (TSH), which, in turn, stimulates the thyroid to secrete more T3 and T4. Once the thyroid hormones reach a certain level in the blood, TSH production drops.

The pituitary gland is regulated by still another gland – the hypothalamus. The hypothalamus produces TSH Releasing Hormone (TRH), which acts by telling the pituitary gland to stimulate the thyroid gland to release TSH. These functions turn off and on, keeping hormones at a normal level.

Your fertility specialist will evaluate thyroid function through a blood test to measure hormone levels.  A thyroid exam may also be performed to look for enlargement or nodules. Additional tests may be needed depending on your symptoms and test results.

Hypothyroidism and Reproduction

When the thyroid produces subnormal levels of T3and T4, the condition is know as hypothyroidism. Symptoms of hypothyroidism include fatigue, weight gain, irregular periods, low sex drive, infertility and miscarriage.

Low thyroid hormone production can interfere with ovulation by preventing egg release. It can also affect embryonic development, increasing the risk of miscarriage. Premature delivery, low birth weight and diminished fetal mental capacity are also associated with the condition.

Hypothyroidism is treated through thyroid replacement therapy. The condition can usually be managed by taking a single daily pill.

Hyperthyroidism and Reproduction

Hyperthyroidism, or overactive thyroid, is much less common than hypothyroidism. This condition occurs when the thyroid is producing too much hormone, leading to decreased levels of TSH. The excess hormones cause metabolism to speed up, leading to weight loss, sleep difficulties, irregular heart rate and hot flashes.

Hyperthyroidism can interfere with reproduction through infrequent periods and increased energy needs. If hyperthyroidism is severe, radioactive iodine may be used to kill the thyroid. Following this, your reproductive endocrinologist may suggest waiting six months before attempting to get pregnant. Some medications used to treat hyperthyroidism may also be harmful to fetal health. Your fertility specialist will work with you to adjust doses to reduce the risk of complications.