Hypothyroidism: how does thyroid health affect your fertility?

Thyroid is a gland that is found in the neck and is responsible for regulating the body’s metabolism. Its alteration can cause hypothyroidism and hyperthyroidism. The thyroid gland produces two hormones: triiodothyronine (T3) and thyroxine (T4). These hormones play an important role in metabolism. Metabolism is the body’s ability to transform food into energy. The thyroid gland is controlled (regulated) by the thyroid stimulating hormone (TSH). TSH is produced by the pituitary gland, which is found in the brain. 


Types of thyroid dysfunction

The alterations of the thyroid gland are classified into two groups. Hyperthyroidism occurs when excessive amounts of thyroid hormones are produced and this causes the metabolism to accelerate. Hypothyroidism, on the other hand, is the condition in which the thyroid gland does not produce enough hormones, so the metabolism slows down considerably.

Hypothyroidism is more prevalent in women, and is usually more linked to women’s reproductive system. The annual incidence and prevalence of clinical hypothyroidism (which produces symptoms) is between 0.41% and 1.8% for women, and 0.06% and 0.1% for men respectively. Subclinical hypothyroidism (which is asymptomatic) has a prevalence of 7.5% in women and 2.8% in men.


What are the symptoms of hypothyroidism?

When the thyroid gland produces less thyroid hormone than it should (hypothyroidism), the metabolism slows down, which can cause a variety of symptoms. At first, hypothyroidism symptoms may not manifest or go unnoticed (subclinical hypothyroidism), but over time these symptoms may be more obvious and severe and may include the following:

  • Fatigue (tiredness)
  • Weight gain
  • Constipation
  • Irregular periods
  • Loss of sexual desire
  • Hair loss
  • Brittle hair and nails
  • Itching and dry skin
  • Difficulty in learning and remembering
  • Sterility
  • Miscarriage and recurrent miscarriage


What causes hypothyroidism?

The most common cause of hypothyroidism is an autoimmune disease called Hashimoto’s thyroiditis. The immune system mistakenly sends antibodies to destroy the cells in the thyroid gland. This can cause an enlargement of the thyroid gland, known as a goiter.

Hypothyroidism and goiter can also be the result of not getting enough iodine in your diet. Hypothyroidism can also occur after thyroid surgery or radioactive iodine therapy that are used to treat hyperthyroidism. In many cases, the specific cause of hypothyroidism is not known.


How is hypothyroidism diagnosed?

The main test used to detect hypothyroidism is the measurement of blood levels of TSH (Thyroid-Stimulating Hormone). A high TSH level usually means that the thyroid gland does not produce enough thyroid hormone, and the pituitary gland has responded by making more TSH to try to get the necessary levels of the thyroid hormone.

Other blood tests include the measurement of T4 and anti-thyroid antibodies. Antibodies are substances produced by the immune system, usually to protect against bacterial and viral infections. Sometimes, however, the immune system can produce antibodies against your own body, such as against your thyroid.


How does hypothyroidism affect fertility and pregnancy?

Hypothyroidism can lead to menstrual disturbances and anovulation. Usually, for women who have regular periods (menstruated every month), an egg is released from the ovary every month. However, women who have hypothyroidism may release an egg less often or not release it.

Hypothyroidism can also interfere with the development of an embryo (fertilized egg). This increases the risk of miscarriage. Also, if you are pregnant and your hypothyroidism is not treated, your baby may be born prematurely, weigh less than normal, and suffer from neurodevelopmental disorders.

It is very important that patients seeking pregnancy and pregnant women perform controls to check that thyroid function is normal, and if any alteration is detected, it can be diagnosed and treated properly.


How to treat hypothyroidism?

The most commonly used medication to treat hypothyroidism is called levothyroxine. Levothyroxine is a pill that is usually taken once a day. Once you start taking levothyroxine, blood tests should be done in 4-6 weeks to measure the level of thyroxine and ensure that you are taking the correct dose.

Controls of the thyroid function and its treatment should always be supervised by your general practitioner or your endocrinologist.


Is it necessary to continue controlling my thyroid?

It is important to perform regular checks, even after the correct dose has been found. Hypothyroidism is often a permanent and progressive disease and the dose of medication needed to ensure proper functioning can vary over time.

If you become pregnant, your doctor will have to monitor your thyroid function every quarter as well as your dose of levothyroxine. This is because your needs may change due to pregnancy.


Seen the relationship between thyroid dysfunction and fertility, it is highly recommended to perform a test to check the proper functioning of thyroid function, in order to rule out possible complications. In any case, the best option is always to consult with a professional.

If you have more questions, please do not hesitate to contact us.

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