This article takes you through hypothyroidism, in terms of its symptoms, diagnosis and treatment. Learn about the evidence linking this condition to problems with male and female fertility, and the impact it can have on pregnancy and fetal and infant development.

Introduction

What is hypothyroidism, and what impact does it have on reproductive health? In this article, we take you through this condition, in terms of its symptoms, diagnosis and treatment. We also discuss the evidence linking an underactive thyroid to problems with male and female fertility, and the impact it can have on pregnancy and fetal and infant development.

Let’s start by looking at the thyroid gland in general.

What is the thyroid gland, and what does it do?

The thyroid gland is a butterfly-shaped organ located at the base of the neck. It produces hormones that are important for growth, development and metabolism.

The following hormones are produced by the thyroid gland:

  • Triiodothyronine (also called T3)
  • Tetraiodothyronine (also called thyroxine or T4)
  • Calcitonin

Of these, T3 and T4 are directly involved in metabolism, the processes of energy conversion and use in the body. The production of T3 and T4 is regulated by thyroid-stimulating hormone (TSH), which is produced by the pituitary gland. TSH stimulates the thyroid gland to produce thyroxine (T4), which the body converts into triiodothyronine (T3). It is T3 that then directly influences functions related to metabolism, including:

  • Body temperature
  • Heart and pulse rate
  • Brain development (in children and adolescents)
  • Growth of the body (in children and adolescents)
  • How the body uses food

Normally, TSH and T4/T3 work in a negative feedback loop, meaning that TSH production increases when blood concentrations of T4 and T3 are low and decreases when blood concentrations of T4 and T3 are high. If there are abnormalities in the system, also known as thyroid disorders, this negative feedback loop may be disrupted. This occurs in two primary forms:

  • In hyperthyroidism, or overactive thyroid, thyroid hormones are overproduced.
  • In hypothyroidism, or underactive thyroid, the thyroid gland produces insufficient amounts of thyroid hormones.

This article focuses on the latter problem.

What is hypothyroidism?

Hypothyroidism can be classified into different types:

  • Primary hypothyroidism. In this type, the thyroid gland fails to produce sufficient amounts of thyroid hormones. This is the cause of over 99% of cases of hypothyroidism.
  • Secondary hypothyroidism. In this kind, there is underproduction of thyroid-stimulating hormone (TSH) by the pituitary gland. As a result, the thyroid gland is not properly stimulated to produce thyroid hormones.
  • Tertiary hypothyroidism. This is rare, and involves decreased production of thyroid-releasing hormone by the hypothalamus in the brain.

The prevalence of hypothyroidism in Europe is approximately 5% of the population; it is believed that a further 5% of the population may have undiagnosed hypothyroidism. Hypothyroidism occurs up to eight or nine times more commonly in women than in men, and new cases are most often seen between 30 and 50 years of age.

What are the symptoms?

People with hypothyroidism may have no symptoms, or they may experience symptoms such as:

  • Fatigue
  • Muscle weakness
  • Weight gain
  • Cold intolerance
  • Constipation
  • Dry skin
  • Weight gain
  • Enlargement of the thyroid gland, known as goiter

Hypothyroidism has implications for all of the organ systems in the body, with the evidence for increased risk of cardiovascular problems being quite strong. Therefore, it’s advisable to seek medical advice if you have symptoms of hypothyroidism.

What causes hypothyroidism?

The main causes of hypothyroidism are:

  • Iodine deficiency. Dietary iodine is needed by the body in order to produce thyroid hormones. When individuals become iodine-deficient, goiter, thyroid nodules, and hypothyroidism can be the result. Although certain foods—notably salt—fortified with iodine are available, deficiency is still seen at relatively high levels in Africa, Asia and Europe. Worldwide, approximately 2 billion individuals are believed to suffer from iodine deficiency.
  • Hashimoto’s thyroiditis. This is the most common cause of hypothyroidism in areas where iodine tends to be sufficient. Also known as chronic autoimmune thyroiditis, this is a condition in which antithyroid antibodies form and attack the thyroid gland, compromising its ability to function. The thyroid gland often becomes enlarged.
  • Treatments for hyperthyroidism. Treatments for this condition may involve radiation or surgical removal of the thyroid gland, resulting in a chronic lack of thyroid hormones in the body.

What are the risk factors?

Risk factors for hypothyroidism include

  • Being female
  • Increasing age
  • Insufficient dietary iodine
  • Family history of autoimmune disorders, in the case of Hashimoto’s thyroiditis

What is the impact of hypothyroidism on fertility?

Thyroid functioning is important to reproductive functions in both females and males. In this section, we review how hypothyroidism can disrupt fertility in both sexes.

Impact on female fertility

Research has established that an underactive thyroid can disrupt female fertility in the following ways:

Thyroid disorders, including hypothyroidism, are also implicated in endometriosis, which presents its own challenges to female infertility.

Studies have shown that hypothyroidism and subclinical hypothyroidism tend to be more prevalent in women experiencing infertility compared to women who are not. While it seems to be the case that pregnancy is more difficult for women with hypothyroidism to achieve and maintain, the evidence is mixed, and there are some encouraging results, especially among women whose hypothyroidism is appropriately treated.

One study looked at in vitro fertilisation (IVF) in two groups of women: those with clinical or subclinical hypothyroidism being treated with levothyroxine, and those who had normal levels of thyroid hormone without medication (clinically referred to as euthyroid). The study found that a higher proportion of women in the hypothyroid group did not obtain viable embryos. However, it also concluded that when an IVF procedure was started, the rates of clinical pregnancy, implantation and live birth did not differ significantly between the groups. Thus, while hypothyroidism may prevent challenges to female fertility, when it is adequately treated, women are still very much able to become pregnant and carry their pregnancies to term.

Impact on male fertility

Hypothyroidism is far less common in males, but where it exists, it can pose problems to fertility. To begin with, primary hypothyroidism has been found to be associated with decreased libido or sex drive, as well as with erectile dysfunction. A study also found that hypothyroidism was associated with suboptimal sperm morphology, or size and shape; in the same study, this aspect of sperm health improved significantly after treatment.

Another study found that in addition to differences in morphology, additional sperm parameters, such as sperm count and motility, also differed significantly between men with hypothyroidism and those without. As all of these factors can make achieving pregnancy more difficult, it’s recommended that men with symptoms of hypothyroidism who wish to contribute to pregnancy consult with a doctor.

How is hypothyroidism diagnosed?

The symptoms of hypothyroidism are nonspecific, meaning that they could indicate thyroid disease but could also be due to other causes. For this reason, diagnosis is carried out by means of a blood test, also known as a thyroid function test. This involves measuring the level of thyroid-stimulating hormone (TSH). When the TSH level is found to be high, it suggests that there isn’t enough T4 in the blood, and that the thyroid gland is being asked to increase production of T4 to compensate. A T4 test is usually done as a next step, to confirm this.

Subclinical hypothyroidism may also be diagnosed in cases where thyroid-stimulating hormone levels are above the normal range, but T4 remains in the normal range. This condition is often seen as a clue that a person might develop hypothyroidism in the future.

What is the treatment?

Medication

The most common treatment for hypothyroidism is a medication called levothyroxine, which is usually prescribed in pill form and taken once a day, on an empty stomach. This medication is a synthetic form of the T4 lacking in the body. Individuals often experience relief from symptoms within a matter of weeks of starting to take levothyroxine. It’s important to note that this treatment does not cure the condition and instead has to be continued, often on a lifelong basis.

The dose of levothyroxine may have to be adjusted over time. During pregnancy, a higher dose may be needed. TSH levels are therefore monitored periodically in individuals taking this treatment, in order to ensure that they remain in the normal range. If individuals begin experiencing signs of hyperthyroidism, this can be a sign that the dose needs to be adjusted.

Whether subclinical hypothyroidism should be treated is an issue of debate. Among pregnant women, some research has shown that treating it could help to prevent pregnancy loss.

Lifestyle treatments

Lifestyle treatments for hypothyroidism are sometimes suggested. A common one is that women with hypothyroidism, especially that due to Hashimoto’s thyroiditis, should follow a gluten-free diet. However, the scientific evidence regarding this is so far not convincing.

There is somewhat more support for an anti-inflammatory diet and supplementation of missing minerals. For example, selenium, when given in addition to levothyroxine, led in one study to a significant reduction in the level of thyroid autoantibodies (responsible for disease activity) in patients with Hashimoto’s thyroiditis. The evidence regarding this is, however, considered to be still incomplete. The same is true of Vitamin D, which has been associated with thyroid peroxidase (i-TPOAb) antibodies in Hashimoto’s thyroiditis, although the effect of supplementation has not yet been extensively studied.

In general, it’s a good idea to discuss any lifestyle modifications that you might be considering for suspected or known thyroid dysfunction with your doctor or endocrinologist.

Commonly asked questions

If I have hypothyroidism, will I still be able to get pregnant?

It is entirely possible to achieve pregnancy despite hypothyroidism in one or both partners. However, given the evidence—reviewed in the next section—that the condition can impact pregnancy outcomes and fetal and infant health, it’s important that suspected thyroid problems are investigated and addressed. Additionally, existing hypothyroidism should be appropriately monitored both before and during pregnancy.

If I get pregnant with hypothyroidism, will I have a healthy pregnancy?

Research suggests that poorly controlled hypothyroidism during pregnancy can be associated with certain negative outcomes in both early pregnancy and later pregnancy, including pregnancy loss and preterm rupture of membranes.  In addition, there is evidence showing that infants born to mothers with subclinical hypothyroidism have decreased neurological development in the first year of life compared to those born to mothers who are euthyroid (without thyroid imbalance). There are also studies linking insufficient thyroid hormone levels during pregnancy to impaired psychomotor skills in infancy, as well as to symptoms of attention-deficit/hyperactivity disorder (ADHD) in childhood.

If a woman with known hypothyroidism becomes pregnant, her doctor will usually monitor her TSH levels throughout pregnancy, as treatment may need to be adjusted in order to ensure she has enough thyroid hormone.

Levothyroxine, the main medication prescribed for hypothyroidism, is approved for use during pregnancy. Its use is associated with a decreased risk of pregnancy loss and neonatal death for mothers with subclinical hypothyroidism and their babies.

What is the difference between hypothyroidism and normal symptoms of pregnancy?

Certain symptoms of hypothyroidism, including constipation, weight gain, and fatigue, are also common during pregnancy. Symptoms such as cold intolerance and slow heart rate are more indicative of hypothyroidism. Whether the symptoms existed before pregnancy, and their severity, may also help to indicate whether a woman’s thyroid function should be tested.

Is screening for thyroid problems a routine part of fertility treatment?

It has been suggested that screening should form a part of fertility assessment, especially in women experiencing menstrual disturbances that indicate a lack of ovulation. If you are experiencing infertility, this is a topic you may wish to discuss with your fertility doctor, especially if you are experiencing symptoms of hypothyroidism.

Takeaway

Hypothyroidism is a condition in which thyroid hormones are produced at lower levels than necessary, resulting in symptoms such as fatigue and weight gain. It can originate from different causes, such as the thyroid antibodies produced in Hashimoto’s thyroiditis, or iodine deficiency. The treatment is oral levothyroxine, which can be continued through pregnancy. Low levels of thyroid hormone can affect both male and female fertility. When hypothyroidism is untreated, menstrual irregularities can occur, sperm quality can be affected, and outcomes such as pregnancy loss can occur. Timely treatment of hypothyroidism can help to reverse or prevent these outcomes.

At Cada, our caring team puts individuals at the centre of their fertility care. Would you like to discuss this issue or others concerning reproductive health and fertility? Reserve your free consultation today and get in touch with us so that we can figure out how best to help you.