How Your Thyroid Affects Egg Quality and Fertility

In this article

Thyroid disorders are more common than you may realize, affecting many millions of people worldwide. These conditions can have far-reaching effects on various aspects of health, including fertility. For women trying to conceive, understanding the relationship between thyroid function, egg quality, and overall fertility is crucial. This article delves into the intricate connections between thyroid disease and reproductive health, exploring how thyroid dysfunction can impact your egg quality and fertility and affect your chance of having a healthy pregnancy. 

The thyroid, a small butterfly-shaped gland located at the base of the neck, plays a vital role in regulating numerous bodily functions by producing thyroid hormones. These hormones, primarily thyroxine (T4) and triiodothyronine (T3), are essential for proper metabolism, growth, and development.

Thyroid hormones play a crucial role in regulating the reproductive system and can affect fertility in several ways. 

Menstrual cycle irregularity

Your thyroid’s hormone levels impact your menstrual cycle significantly. Women with thyroid disorders may experience oligomenorrhea (irregular or infrequent periods) or amenorrhea (absence of periods). Both irregularities can make it challenging to predict fertile windows and conceive.

Ovulation disruption

Ovulation relies on the proper functioning of thyroid hormones, and hypothyroidism can affect fertility by disrupting ovulation. If you’re hypothyroid, you might experience irregular or absent ovulation (anovulation), making conception significantly more difficult. 

Elevated prolactin levels

Hypothyroidism is linked to elevated prolactin levels in as many as 20% of patients. This connection is primarily due to the increased production of thyrotropin-releasing hormone (TRH), which stimulates both TSH and prolactin secretion, among other effects. High prolactin levels can stop an egg from being released from the ovary and traveling down the fallopian tube, making it harder for ovulation to happen. Without ovulation, conception is impossible.

Implantation

Your thyroid hormone levels can influence implantation success. Proper thyroid function is essential for creating ideal conditions for implanting a fertilized egg.

Early embryonic development

Thyroid hormones impact the early stages of development of an embryo. Thyroid hormones play a crucial role in fetal development. However, dysfunction of the thyroid, particularly hypothyroidism, can significantly raise the risk of miscarriage and other complications during early pregnancy.

Luteal phase defects

Hypothyroidism can cause luteal phase defects, making it harder to conceive. The luteal phase of your period happens between ovulation and the start of your next menstrual period. During this time, the uterine lining thickens to prepare for potential pregnancy. Without sufficient thyroid hormones, the luteal phase can be shorter. This shortened phase may not provide enough time for the uterus to prepare adequately for pregnancy, potentially resulting in early miscarriage or failure to conceive.

Increased risk of miscarriage

Untreated hypothyroidism can increase the risk of losing a pregnancy. Thyroid hormones are essential for the fetus to grow and develop, especially in the early stages of pregnancy. If there aren’t enough thyroid hormones, it can cause problems that might lead to pregnancy loss. This is especially concerning for women who are trying to conceive or are in the early weeks of pregnancy.

Autoimmune thyroid disorders, such as Hashimoto’s thyroiditis, can have additional impacts on fertility beyond hormone imbalances.

Increased risk of premature ovarian failure

Research suggests that autoimmune mechanisms may contribute to both Hashimoto’s disease and premature ovarian failure. These mechanisms could involve genetic factors and environmental triggers affecting both thyroid and ovarian function. This highlights the critical role of thyroid health in maintaining healthy ovarian activity and fertility. 

Cross-reactivity with ovarian tissue

Thyroid autoimmunity doesn’t only affect the thyroid gland—it may also impact ovarian tissue. Research indicates that thyroid antibodies, produced in response to thyroid autoimmunity, can harm ovarian function and egg quality. This can make it harder for women with Hashimoto’s to conceive, as poor egg quality reduces fertilization rates and leads to less viable embryos.

Implantation issues

For women with Hashimoto’s thyroiditis, even successfully fertilized eggs may face obstacles during implantation. Research shows that Thyroid antibodies have been associated with a reduced ability of embryos to implant in the uterus, possibly due to immune system dysfunction or altered uterine receptivity. Additionally, Hashimoto’s has been linked to an increased risk of early pregnancy loss, including miscarriages within the first trimester. This could stem from disruptions in hormone levels essential for pregnancy or inflammatory responses caused by thyroid autoimmunity.

‍Thyroid function impacts egg quality. Recent research has shed light on the direct effects of thyroid hormones on egg quality and ovarian function.

T3 and follicular development

The thyroid makes triiodothyronine, or T3, the active hormone. T3 plays a crucial role in the development of ovarian egg follicles. Studies show that exposure to T3 increases follicle volume, playing a key role in follicular growth and maturation. Low T3 levels, common in hypothyroidism, may make ovulation and fertilization more difficult. 

T3 and granulosa cells 

Additionally, T3 helps protect granulosa cells. These cells, located in the ovaries, surround and support the developing egg. They produce essential female sex hormones, including estrogen and progesterone, and provide nutrients and hormones to the eggs. Healthier granulosa cells together enhance the chances of successful ovulation and fertilization.

When your thyroid is underactive, and you don’t have enough thyroid hormone, granulosa cells don’t respond well, making it harder for eggs to develop properly.

TSH levels and embryo quality

Research has indicated that thyroid-stimulating hormone (TSH) levels, even within the normal range, can impact embryo quality:

• Women with high-normal TSH levels (between 2.5 and 4.5 μIU/mL) may experience reduced embryo quality.
• The presence of thyroid peroxidase (TPO) antibodies can further affect embryo quality, particularly in women with low-normal TSH levels.

Given the significant impact of thyroid function on fertility, it’s crucial to screen for thyroid disorders in patients experiencing fertility issues. 

TSH testing

The primary screening test for thyroid function is the measurement of TSH levels. The general normal range for TSH is 0.5 to 5.5 μIU/mL. For women trying to conceive or during early pregnancy, the optimal TSH range is narrower and recommended to fall between 0.5 and 2.5 μIU/mL.

Additional thyroid function tests

In cases where TSH levels are abnormal, or thyroid dysfunction is suspected, additional tests may be performed:

• Free T4 and Free T3 levels
• Thyroid antibody tests (TPO and thyroglobulin antibodies)

These tests provide a more comprehensive picture of thyroid function and can help identify autoimmune thyroid disorders.

Optimizing your thyroid treatment is essential for optimal fertility outcomes.

• Thyroid hormone replacement: Levothyroxine, the recommended treatment for hypothyroidism in pregnant women, should be carefully dosed to achieve optimal TSH levels.
• Close monitoring: It is essential to get regular thyroid testing during pregnancy, as thyroid hormone requirements often increase, especially during the first trimester. ‍
• Thyroid hormone optimization: Even in cases of subclinical hypothyroidism, where thyroid function is slightly impaired but symptoms are not obvious, women with thyroid antibodies who are trying to conceive may benefit from treatment with levothyroxine.‍
• Monitoring during pregnancy: Women with thyroid autoimmunity require close monitoring throughout pregnancy due to an increased risk of complications.

For patients undergoing in vitro fertilization (IVF) or other assisted reproductive technologies, there are several reasons why it’s crucial to have optimal thyroid function: 

• Embryo quality: As discussed earlier, TSH levels and the presence of thyroid antibodies can affect embryo quality in IVF cycles.
• Implantation rates: Thyroid dysfunction may lead to lower implantation rates and an increased risk of early pregnancy loss.

Some fertility clinics routinely screen for thyroid disorders as part of their initial workup for IVF patients. This workup typically includes:

• TSH testing
• Thyroid antibody screening, particularly in women with a history of thyroid disorders or autoimmune conditions

For a detailed discussion of how IVF is affected by Hashimoto’s and hypothyroidism, read Thyroid Health and IVF: What You Need to Know at the Paloma blog. 

The role of thyroid autoimmunity in fertility, particularly its effects on egg quality and ovarian reserve, is critical for future research. Studies should focus on:

• Understanding how thyroid antibodies affect the development and maturation of egg follicles 
• Investigating the potential impact of thyroid autoimmunity on ovarian reserve 

Developing new and more effective treatments for optimizing thyroid function in fertility patients is also crucial. Future research directions may include:

• Exploring personalized medicine approaches to thyroid hormone replacement to optimize fertility and egg quality, considering genetic factors and individual metabolic profiles.
• Investigating the potential of combination therapies that address thyroid function and related endocrine imbalances.
• Evaluating the efficacy of novel drug delivery systems for thyroid hormones to improve bioavailability and reduce side effects.

As research in these areas progresses, it is likely to lead to more personalized and effective approaches to managing thyroid function in the context of fertility treatment. This could ultimately result in improved conception rates, healthier pregnancies, and better long-term outcomes for mothers and their children.

The intricate relationship between thyroid function, egg quality, and fertility underscores the importance of comprehensive thyroid evaluation in patients planning to conceive. From the direct effects of thyroid hormones on follicular development to the impact of thyroid autoimmunity on embryo quality, maintaining optimal thyroid function is crucial for reproductive success.

If you’re trying to conceive, whether naturally or through assisted reproductive technologies, understanding and addressing any underlying thyroid issues can significantly improve your chances of a successful pregnancy. This is where Paloma Health can make a profound difference. Offering convenient and comprehensive at-home thyroid testing, Paloma Health empowers you to gain critical insights into your thyroid health easily and frequently, without the hassle of visiting a lab or clinic. Paloma’s tests evaluate key thyroid biomarkers, including TSH, free T3, free T4, and thyroid antibodies, ensuring a comprehensive understanding of thyroid function.

Beyond testing, Paloma Health gives you access to expert thyroid care, including personalized treatment plans tailored to optimize your thyroid health. Paloma’s specialized focus on thyroid conditions ensures that you receive the targeted attention needed to address even subtle dysfunctions, which can have profound effects on successful conception and pregnancy. 

Healthcare providers should be vigilant in screening for and managing thyroid disorders in fertility patients. As a Paloma Health member, this process is simplified and enhanced for you. As research in this field continues to advance, the integration of accessible thyroid evaluation and expert management will likely become even more essential, leading to more targeted and effective treatments for those facing thyroid-related fertility challenges.

• Thyroid hormones are essential for regulating the menstrual cycle, ovulation, implantation, and early embryonic development, making proper thyroid function critical for fertility and pregnancy success.
• Hypothyroidism can lead to ovulation disruption, elevated prolactin levels, and luteal phase defects, all of which reduce the chances of conception and increase the risk of early pregnancy loss.
• Autoimmune thyroid disorders like Hashimoto’s can harm ovarian function, egg quality, and embryo implantation due to thyroid antibodies and immune system dysfunction, increasing the risk of miscarriage and infertility.
• Thyroid hormones, especially T3, play a key role in egg follicle development and granulosa cell health, both of which are essential for ovulation, fertilization, and embryo quality.
• Comprehensive thyroid screening, including TSH and thyroid antibody tests, is vital for women experiencing fertility issues, with levothyroxine being a standard treatment to optimize thyroid function for conception and pregnancy.
• For women undergoing IVF, optimal thyroid function is critical for embryo quality and implantation success, making routine thyroid evaluations an essential part of fertility care.