Female Fertility Health: Can Thyroid Hormone Levels Be Affecting Your Fertility Health?
Many things can affect our fertility; there are ways to help improve your chances of conceiving, and also, many ways to assess why you might be having trouble conceiving. Some potential causes of infertility are more well researched than others, and more recently, there are new issues surfacing that can cause potential issues with conception. One of these issues are thyroid hormones.
The thyroid hormone is a major part of your endocrine system and manages the body’s metabolism (rate at which your metabolism works). Thyroid hormone helps your body turn the food that you consume into energy that your body uses for many physiological processes. Your thyroid releases two main hormones that are known as thyroxine (T4) and triiodothyronine (T3), making up your thyroid hormone. Once your body releases T4, different organs in your body turn it into T3, which is the active form of your thyroid hormone.
The mechanism at which thyroid hormones are released is through a feedback loop. Your hypothalamus releases thyroid-releasing hormone (TRH). TRH stimulates the pituitary gland to make and release thyroid-stimulating hormone (TSH) which thereby triggers the production of T4 (80%) and T3 (20%). When T3 and T4 increase to adequate levels, the feedback loop stops TRH, and thereby TSH, from producing anymore T3 and T4. Therefore, if there are any issues with your hypothalamus, pituitary gland, or thyroid, this can create an imbalance in your thyroid hormone levels causing dysfunction of certain bodily processes. Some symptoms of thyroid hormone imbalances are, but not limited to, unexplained weight gain or loss, decreases or increases in heart rate, dry/moist skin and brittle hair, irregular menstrual cycles, etc. Laboratory testing can assess your thyroid functioning and levels of Total T4, Free T4, Total T3, Free T3, TSH, Reverse T3, Thyroid Antibodies, and Thyroglobulin. By viewing these levels, your healthcare provider can better understand the health of your thyroid.
How does this relate to your fertility? Well studies on the subject are continuing to emerge, drawing an association of increased TSH and/or thyroid autoimmunity to infertility, low ovarian reserve, impaired ovulation, and in men, sperm chromosomal abnormalities. These studies are bringing a new perspective and understanding to the pathogenesis of thyroid levels and it’s impact on fertility.
Thyroid dysfunction or disease is increasingly common in women of reproductive age, and infertility is seemingly more common in women with thyroid hormone imbalances. But it isn’t just female fertility that is affected, can also affect male fertility (a topic that I will focus on in another blog post). Testing of the thyroid hormone doesn’t just end after conception; studies have shown the negative impacts of subclinical hypothyroidism and thyroid peroxidase (TPO Ab) antibody levels on obstetrical outcomes and fetal health. It is recommended that TSH be tested now in early pregnancy, and anti-TPO levels in high-risk women.
A large retrospective study found that in those with hypothyroidism (high TSH) with levels between 4.1-10 mIU/L had an increased chance of miscarriage. However, chance of miscarriage decreased with conventional treatment measures. A grouping of other studies looking at thyroid autoimmunity and fertility found increased infertility and low ovarian reserve in the women who were studied. It is important to mention that some large RCT’s found that women who did not have thyroid hormone imbalance but were positive for anti-TPO Ab failed to show a positive effect of conventional treatment in the improvement of miscarriage and live birth outcomes. Interesting right? Let’s dive a bit deeper into the physiology of how these hormone levels affect fertility.
The ovary is made up of a variety of different cells, and some of these cells express the TSH receptors. These proteins are regulated differently throughout the different stages of follicular development. In addition, the endometrium also has these proteins that are regulated differently throughout the different stages of the menstrual cycle. By expressing these proteins(receptors) for TSH means that thyroid hormones have the ability to affect these stages of reproductive health that your body goes through in follicular development and menstrual regulation.
When it comes time for conception, the thyroid hormone continues to play a role. The thyroid hormone is involved in the implantation of the fertilized egg and in early fetal development/health via the placenta and endometrium. In other words, the thyroid hormone helps determine the susceptibility of the endometrium to take on and grow a fertilized egg into a healthy fetus. Research has agreed upon an association between thyroid levels and fertility and fetal health, but what they have also begin to show is that the thyroid itself is also regulated by our reproductive hormones. Studies have assessed human chorionic gonadotropin (hCG) hormone, and found that because of its similarity in structure to TSH, actually cross reacts with the TSH receptor, creating a relation of hCG levels and free T4 levels, and an inverse association of hCG and TSH in pregnancy. This relationship is found to be affected in thyroid autoimmunity; the regular hCG and free T4 levels seen in women without thyroid autoimmunity were reduced in anti-TPO positive women. In these women, there was a lack of appropriate response to hCG, leading to a greater risk of preterm delivery. Another study found that thyroglobulin antibodies also lead a dysfunctional hCG response. These studies not only educate us on the varying effects that thyroid levels can have on fertility and fetal development, but they also explain to us the importance of a balance in our reproductive hormones and their roll in relation to the thyroid.
This is an exciting time in research, as more studies are surfacing about the impact of thyroid health on fertility, and the importance of fertility-based hormone panels that are inclusive of thyroid hormone. These advances in knowledge may help your healthcare provider better understand where conventional and/or naturopathic medicinal support is warranted.
What does a comprehensive hormone panel for fertility look like? Typically, when issues of infertility arise or just to check fertility health, naturopathic doctors order blood work that is conclusive of, but not limited to:
Note: Other hormones are tested based on an individual basis. This blog post and accompanying table is more focused on female fertility health. As indicated in current research, other thyroid levels may be beneficial in testing when assessing fertility health.
Main Resources:
1. Cleveland Clinic (2022). Thyroid Hormone.
2. Dosiou, C (2020). Thyroid and Fertility: Recent Advances. Mary Ann Liebert Inc., 30(4).
Disclaimer: It is best to consult with your naturopathic doctor or healthcare provider before implementing anything new into yours or your child's healthcare plan. This information is not intended to treat or diagnose, and should not replace any currently prescribed protocols from your healthcare team. All information here is presented in an easy to read format; for those interested in evidence that supports this information, please contact us at ca@nadarra.health for citations or book an appointment to learn more.
