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The Role of Thyroid in Fertility

Jason Dobruck

The thyroid produces several hormones that regulate energy usage throughout the entire body. Because of this, irregular thyroid activity and/or imbalance of thyroid hormones can negatively affect virtually every bodily function. The regions most impacted by thyroid dysregulation tend to be neurological activity, weight regulation and energy level. However, the thyroid also plays a significant role regarding fertility and may be associated with one’s reproductive difficulties.

Connecting the Thyroid to Fertility

In recent surveys of thyroid research, it was stated that the thyroid has notable influence over various aspects of fertility in both men and women. Thyroid dysfunction has been implicated in contributing to a wide range of fertility issues including but not limited to anovulatory cycles, sex hormone imbalances, low sperm density, and abnormal sexual development. The critical role of the thyroid in these and other areas makes it imperative that we understand that influence of the thyroid over both female and male fertility.

Thyroidal Influence on Female Fertility

Studies suggest that any form of thyroid dysfunction may impede female fertility. However, decreased thyroid activity, or hypothyroidism, appears to be the primary concern. A decline in thyroid function slows many bodily processes which can contribute to fertility issues such as luteal phase defects, hyperprolactinemia, and sex hormone balance. In addition to hypothyroidism, studies suggest that the more common subclinical hypothyroidism, which is not easily detectable through standard testing, can also cause serious fertility issues. Women are approximately three times more likely than men to have thyroid issues but sadly many of these cases go undiagnosed.

Although less common than hypothyroidism and subclinical hypothyroidism, autoimmune thyroid disease, specifically Hashimoto’s thyroiditis and Graves’ disease, a relatively common issue amongst infertile women. These conditions assault the thyroid gland and can cause erratic changes in thyroid hormone values. Research suggests that these conditions are notable contributors to infertility and the occurrence of miscarriage.

If you are a hopeful mother with a thyroid condition do not lose hope! Alleviating thyroid-related infertility is often possible. One study composed of nearly 400 infertile women, over 23% of which tested positive for hypothyroidism, found that after attending to thyroidal imbalances nearly 77% of the test population was able to conceive within a year. This strongly suggests that infertile women whose reproductive issues stem from hypothyroidism and even autoimmune thyroid disease may see notable improvement of pregnancy outcomes through appropriate treatment.

Thyroid Concerns During Pregnancy

During pregnancy, the thyroid gains even greater importance regarding female fertility. It is widely agreed that maintaining healthy thyroid function and appropriate thyroid hormone values during pregnancy is critical for positive outcomes.

Thyroid Stimulating Hormone or TSH is one of the primary metrics used to assess thyroid function. Increased TSH values during pregnancy, indicative of thyroid dysfunction, is associated with a variety of issues including miscarriage.

Pregnant women with subclinical hypothyroidism, defined as TSH levels greater than 4 mlU/L, have greater risk of unsuccessful pregnancy when compared to women with normal TSH values. Current guidelines state that TSH values for pregnant women should not exceed 2.5 mU/L during the first trimester and go no higher than 3.0 during the second and third.

A study evaluating over 50,000 hypothyroid women further defines the connection between TSH values and the risk of miscarriage. During the first trimester, nearly 63% of the participants had TSH values above 2.5 mU/L. 7% of the study population had TSH levels above 10 mU/L, far above the recommended value. Women who maintained TSH values above 4.51 had a higher incidence of miscarriage when compared to women with TSH values between 0.2 and 2.5 mU/L. Another study presented similar results. 202 of the nearly 4,600 participants presented elevated TSH during weeks 11-13 of gestation. Each of these cases resulted in miscarriage. This contrasts with the other 4,318 pregnant participants with no history of thyroid disease, all of which resulted in live births after 34 weeks.

Experts agree that women who are pregnant should have their thyroid levels checked regularly as to identify and respond quickly to any sort of irregularities. Some experts recommend proactive thyroid therapies to further minimize the risk of thyroid hormone imbalances. Such an approach may be beneficial for improving pregnancy outcomes even if the patient is under the TSH threshold of 2.5 mU/L. However, the validity of proactive thyroid care is not the consensus view and further research is required.

Thyroid Influence on Male Fertility

Women are not the only group affected by thyroid-related fertility issues. Male fertility is also strongly influenced by the thyroid. Thyroid hormone imbalances, both excess or deficiency, are connected to various male fertility issues including altered function of the testis and semen irregularities.

It is well documented that hyperthyroidism, accelerated thyroid function, is implicated in reducing semen volume as well as limiting sperm density, motility, and morphology. One study composed of 25 patients diagnosed with Graves’ disease, an autoimmune disease that induces hyperthyroidism, found that half of the population developed asthenozoospermia. Ssthenozoospermia instigates a reduction in sperm motility and subsequent decline in fertility rates. The researchers posit that the excess thyroid hormone circulating in the bloodstream was a primary contributor. The same study also found that 40% of thyrotoxic patients, those with greatly elevated thyroid hormone values, developed oligozoospermia and teratozoospermia, each of which are associated with reduced semen volume.

Conversely, a decline in thyroid function has also been shown to inhibit male fertility. Studies show that hypothyroidism, slowed or limited thyroid function, is associated with a reduction in sperm morphology, sperm vitality and movement of sperm through the epididymis. Each of these factors are pivotal elements of male fertility and can greatly limit reproductive success.

The significant influence that both hyperthyroidism and hypothyroidism have on male fertility makes it clear that thyroid testing for any man experiencing fertility difficulties. Any man interested in procreation should make thyroid health a priority.

Improving Fertility by Supporting Your Thyroid

The thyroid is a powerful regulator of numerous bodily functions including many that affect fertility. Although thyroid issues are more common in women, it is important that both men and women recognize the powerful influence of the thyroid on their reproductive ability. Those struggling to conceive should strongly consider having their thyroid evaluated. For many men and women proper treatment and normalization of the thyroid may be the key to restoring their reproductive health.


Jason DobruckJason is a freelance writer with experience covering health, food, nutrition, and supplementation for NAHIS, HoltraCeuticals and other wellness outlets. He has been writing medical and health related content for over three years. Jason enjoys covering everything from general health tips to comprehensive condition overviews and treatment options.

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