Is Your Thyroid Impacting Your Fertility?

Thyroid disease is one of the most common conditions that we see in women of reproductive age. The function of the thyroid gland is crucial in terms of optimizing fertility and maintaining a healthy pregnancy. Therefore, individuals who are trying to conceive or who are currently pregnant should have their thyroid hormones tested and treated to correct any imbalance. 

Testing Thyroid Function for Fertility 

Thyroid testing is done through blood work. Because there are many variations of thyroid dysfunction, it is recommended to complete a full thyroid panel. This includes: 

TSH (Thyroid Stimulating Hormone)

This hormone is released from the pituitary gland in our brain. It stimulates the thyroid to make and release T4. Optimal range is 1-2. TSH is elevated in hypothyroidism and low in hyperthyroidism.

Free T4

This hormone is released from the thyroid gland. When T4 is low, the thyroid signals back to the pituitary to release more TSH. Optimal range is 15-18.

Free T3

This is the active form of thyroid hormone. Only small amounts of T3 are released by the thyroid, so the majority comes from the conversion of T4 to T3 in the tissues. In order to convert from T4 to T3, the body must use conversion factors such as selenium, zinc, tyrosine and iodine. Optimal range is 4.0-5.5. When T3 is low, people often feel symptoms of hypothyroidism. 

Antibodies (Anti-TPO and Anti-TG)

Antibodies are elevated in autoimmune thyroid disease such as Hashimoto’s thyroiditis or Grave’s disease. It is important to test antibodies to rule in or out these conditions as they greatly affect fertility outcomes. 

Reverse T3

In times of stress and inflammation, the body can convert T3 into reverse T3. This can block the receptor that T3 binds to, and therefore contribute to symptoms of hypothyroidism. Optimal <18.

Why should I complete a full thyroid panel?

In many cases, just TSH is tested to screen the thyroid. But without a full thyroid panel, one can miss a diagnosis of thyroid dysfunction. This is because there are different patterns of hypothyroidism. For example, sometimes in autoimmune thyroid disease the antibodies will be positive but TSH may show up normal. Additionally, there is a condition known as peripheral hypothyroidism where T4 is not converting well into T3 in the tissues. This can result in symptoms of hypothyroidism but TSH and T4 may look normal, while T3 is low. Therefore, a full thyroid panel is crucial to understanding the whole picture. By only testing TSH, you may be missing thyroid dysfunction that could be contributing to fertility challenges. 

Hypothyroidism and Fertility

Hypothyroidism is the most common type of thyroid dysfunction. In this case, the thyroid is sluggish and is not functioning as well as it should be. Every cell in the body requires thyroid hormone. So, when this gland is under-functioning there can be a wide variety of effects in the body. Symptoms of hypothyroidism include:

• Fatigue
• Feeling cold
• Constipation
• Brain fog
• Weight gain or difficulty losing weight
• Heavy periods
• Difficulty conceiving or decreased pregnancy maintenance 
• Dry skin
• Hair loss
• Brittle nails
• Difficulty concentrating 
• Poor memory
• Low appetite
• Low mood
• Worry or anxiety

Thyroid hormones are important for many areas of reproductive health. Lack of thyroid hormone has been shown to impair ovulation rates and contribute to menstrual irregularities¹. Additionally, receptors for thyroid hormone are found in the endometrium and are involved in the implantation process. When the thyroid is not functioning optimally, there is a significant impact on preconception health and pregnancy success.  

The most common cause of hypothyroidism is autoimmune disease. Women with positive anti-TPO or anti-TG antibodies have higher risk for preterm delivery, miscarriage and preeclampsia². Similar outcomes have been associated with subclinical hypothyroidism^2,3,4. Because thyroid conditions can have such profound impacts on fertility outcomes, it is important to test and treat any imbalances. 

Having decreased thyroid function before conception can be a risk for early pregnancy loss. For optimal fertility outcomes, TSH should be less than 2.0 and thyroid antibodies should be negative. 

Hyperthyroidism and Fertility

Hyperthyroidism is less common, but still has significant effects on fertility outcomes. Symptoms of hyperthyroidism include:

• Feeling hot
• Increased bowel movements
• Feeling of heart racing
• Anxiety and nervousness
• Weight loss
• Fatigue
• Excessive sweating 

Menstrual irregularities are 2.5x more common in women with an overactive thyroid. Additionally, the conversion of testosterone to estrogen is increased, resulting in 2-3x higher estrogen than in women without this condition. In men, erectile dysfunction is more common and sperm DNA and motility may be altered⁵. Autoimmune Grave’s disease is the most common cause of hyperthyroidism. TSH will often be low and antibodies such as anti-TPO, anti-TG, thyroid-stimulating immunoglobulin (TSI) and thyroid receptor antibody (TRAb) may be detected in bloodwork. Testing and treating dysfunction is important to optimize fertility and pregnancy outcomes. 

Thyroid Function in Pregnancy

The requirement for thyroid hormone increases by 20-50% during pregnancy⁶. Maternal thyroid hormone is delivered to the growing baby through the placenta. The fetus does not make its own thyroid hormone until around 10-12 weeks gestation. So, optimal maternal thyroid hormone is crucial during this time for early development.

Hypothyroidism during pregnancy can lead to fetal growth restriction, premature delivery and hypertension.  When TPO antibodies are present in pregnancy, there is an increased risk for postpartum thyroid dysfunction. There may also be an increased risk of miscarriage, preterm birth and impaired child neurological development⁶. 

Frequent blood work to investigate thyroid function is important throughout pregnancy, especially in the first trimester. If you are taking thyroid medication such as Synthroid, the dose may need to be adjusted by your doctor. 

Do you need support with your thyroid health for fertility?

As you can see, optimal thyroid function is crucial for fertility and a healthy pregnancy.  I can help you build the most important foundations for achieving balanced thyroid function to support optimal fertility and better health.