Can Thyroid Issues Cause Infertility?; What your doctor missed during your fertility workup

This is because conventional thyroid testing looks for overt thyroid disease, and often misses the subtle thyroid issues that can disrupt ovulation, slow hormone production, prevent conception, and increase the risk of miscarriage. But, can thyroid issues cause infertility?

This blog covers how to more accurately assess your thyroid health, and figure out if thyroid issues are causing infertility. 

Introduction

Hands down, thyroid health is critical to overall health and fertility. 

The thyroid sets the pace for nearly every process in your body. From how quickly your cells convert food into energy, to the rate of hormone production, to the regularity of your menstrual cycle, and so much more –  it’s all regulated by thyroid hormones.  

With this widespread impact throughout your body, thyroid issues can increase the risk of infertility, and a healthy thyroid is essential to a healthy pregnancy. 

Unfortunately, many doctors miss the impact of thyroid issues on your fertility. Too often, thyroid issues go undiagnosed and untreated, and couples struggle for longer than necessary with infertility.

Thankfully, with a complete thyroid evaluation, thyroid-related fertility challenges can often be identified, and then managed, to help you get pregnant more quickly and easily. 

This blog will cover how thyroid issues can cause infertility, the signs to watch for, why thyroid issues are often missed as part of a fertility workup, and how to comprehensively test for even subtle thyroid issues. 

Let’s dive in.

What is Thyroid Hormone? 

The thyroid is a small, butterfly-shaped gland in your neck, just below the Adam’s apple. While it may be small, its role in your overall health – particularly your fertility-  is substantial.

Think of thyroid hormone as setting the pace for nearly every cellular function in your body – including the rate of converting nutrients into energy, making hormones, growing follicles in your ovaries, etc. 

Even subtle disruptions to thyroid hormone levels can throw everything off – your metabolism, digestion, your menstrual cycle, and your reproductive health.  
 

Getting to Know Your Thyroid Hormones: TSH, T4 and T3

The thyroid hormone pathway begins in the brain with thyroid-stimulating hormone (TSH). As the name suggests, TSH travels from the brain to stimulate the thyroid gland to make thyroid hormone. 

The thyroid gland responds to TSH by producing thyroxine (T4), which is inactive, and requires conversion to triiodothyronine (T3) for your cells to put the hormone into use.

Here’s a summary of the of the thyroid hormone process: 

1. Thyroid Stimulating Hormone (TSH) travels from the pituitary gland in the brain to the thyroid gland;
2. The thyroid gland responds to the TSH by producing thyroxine (T4)
3. Thyroxine (T4) travels in the blood stream to the liver, kidneys and GI tract, etc. where it gets converted into triiodothyronine (T3). 

Triiodothyronine (T3) is the active form of the hormone recognized and used by your cells. 

When thyroid hormone (T4) drops, the brain detects the low levels and responds by producing more TSH, to prod the thyroid gland into upping production of T4. 

This is why high TSH levels are often used to indicate low thyroid hormone levels. It’s called a negative feedback loop. 

Common Thyroid Disorders 

Thyroid issues, whether overt or subclinical, are widespread, especially among women. According to the American Thyroid Association, more than 12% of adults in the US have some form of thyroid issue. Women are 5-8 times more likely than men to struggle with thyroid health. 

Here are three of the most common thyroid issues: 

1.  Hypothyroidism

In hypothyroidism, thyroid hormone levels are too low. About 4-8% of the general population have hypothyroid, but an estimated 5-7% of thyroid issues go undiagnosed. 

The leading cause of hypothyroidism is Hashimoto’s thyroiditis, an autoimmune condition (more on this below). 

2.  Hyperthyroidism

Hyperthyroidism, meaning elevated thyroid hormone levels, affects approximately 1-2% of the population in the U.S. 

3.  Autoimmune Thyroid Disorders

Autoimmune thyroid conditions are the most common cause of thyroid problems, and the most common organ-specific autoimmune condition. 

Autoimmune thyroid conditions occur when the immune system mistakenly attacks the thyroid gland, causing inflammation in the gland, often disrupting how much thyroid hormone gets produced. The two most common autoimmune thyroid disorders are: 

• Hashimoto’s thyroiditis: the leading cause of hypothyroidism
• Graves’ disease: the most common cause of hyperthyroidism
  
  

How Thyroid Issues Can Cause Infertility

Since thyroid receptors are found in nearly every cell of the body – thyroid issues can cause infertility in a variety of ways. When thyroid hormone levels are off, it can disrupt everything from ovulation, to progesterone levels for a healthy uterine lining, to the availability of growth factors needed for embryo growth and development.  

Thyroid issues can cause infertility in three primary ways:

1. Disruption of ovulation and menstrual cycle regularity – making it difficult to find your fertile window, and resulting in fewer opportunities for conception each year;
2. Hormonal imbalances leading to difficulty in both conceiving and building a plush uterine lining for a fertilized egg to implant into; and 
3. Increased risk of miscarriage and early loss.  
   
   

Conception is not the end of the story. Since the fetus depends on mom’s thyroid hormone for the first trimester, low thyroid levels can disrupt the baby’s growth and development. Once pregnant, thyroid issues can increase the risk of pregnancy complications, like preeclampsia, low birth weight, and preterm delivery. 

How Autoimmune thyroid disease can cause infertility

For women with autoimmune thyroid disease, it’s not just the thyroid hormone levels that matter. 

Autoantibodies, like thyroid peroxidase antibodies (TPO-Ab), attack the thyroid gland as though it were a foreign invader. 

Not only does this immune response cause inflammation (a barrier to fertility itself), but the presence of thyroid antibodies are also linked to lower ovarian reserve, worse egg quality, and failed fertility treatments.  

This means that even if thyroid hormone levels like TSH, T4 and T3, are within the normal range, elevated antibodies themselves can cause infertility. 

Can thyroid problems cause miscarriage?

As a fertility dietitian, a worry I frequently hear is, ‘Can thyroid problems cause miscarriage?’ (Because, obviously, the goal is not just to get pregnant – you want to stay pregnant.) 

Unfortunately, yes, thyroid problems can increase the risk of miscarriage – if they go untreated. 

Low thyroid levels can decrease progesterone levels, which can increase the risk of early pregnancy loss. Low thyroid levels can also slow the growth of the placenta, which is critical for delivering oxygen and nutrients to the growing fetus, again, increasing the risk for loss. 

If an autoimmune condition is at play, the thyroid antibodies can cause inflammation, which in turn can prevent implantation and disrupt fetal development, again, increasing the risk of miscarriage.

How do I know if I have a thyroid issue? 

How do you know if you have thyroid issues? Here are some common signs and symptoms to look out for, however, to know for sure, “test don’t guess”. 

Signs and symptoms of low thyroid (hypothyroidism) 

Low thyroid levels can show up with a wide range of signs and symptoms, many of which develop gradually, often going unnoticed for too many years. The most common symptoms include: 

• Persistent fatigue
• Weight gain despite no changes in diet or exercise
• Always feeling cold
• Constipation / bloating / sluggish digestion 
• Dry skin, brittle nails, and thinning hair
• Cognitive symptoms, such as difficulty concentrating or memory lapses—sometimes referred to as “brain fog”. 
• Menstrual irregularities, including missed ovulation, long cycles and/or heavy periods. 
• Depression or irritability
  
  

Signs and symptoms of overactive thyroid (hyperthyroidism) 

Similarly, high thyroid levels show up with a variety of signs and symptoms, including:

• Unexplained weight loss, even when eating well;
• Rapid or irregular heartbeat;
• Irritability or restlessness;
• Heat intolerance / excessive sweating;
• Hand tremors;
• Muscle weakness;
• Lighter or less frequent periods.
  
  

Test, Don’t Guess

Given the wide variety of symptoms caused by thyroid issues, the best way to know for sure is with testing – specifically blood work. 

However, BE AWARE! Standard thyroid testing often misses thyroid issues that cause infertility.

When women come to me and say their thyroid is fine because their “TSH was normal”, I have to explain that TSH is not enough to rule out thyroid issues as a part of their infertility puzzle. 

The standard of care is to assess your thyroid health by ordering only two labs: 

• TSH (thyroid stimulating hormone) and
• Free T4 (Thyroxine)
  
  

If both TSH and Free T4 come back within the “normal” range, they say your thyroid is fine… but that’s not always accurate.

This standard approach to thyroid testing is designed to detect overt thyroid disease, but it does not provide a complete picture of thyroid hormone throughout the body, and it misses the more subtle thyroid issues. Concerns with standard thyroid testing include:  

1. It provides an incomplete picture of your thyroid function 

Looking at just TSH and the T4 only tells you if there’s an issue with the thyroid hormone pathway from your brain to the thyroid gland itself. 

Your thyroid gland makes the thyroxine (T4) thyroid hormone, but it’s inactive, meaning your cells can’t do anything with it.

It’s the active triiodothyronine (T3) that your cells recognize and use. So, just testing TSH and T4, does not give you the full picture of thyroid hormone levels. 

It’s possible for your TSH and T4 levels to come back perfectly normal, but your active T3 levels are low. In this scenario, the amount of thyroid hormone circulating in your blood is within the expected range, but you’re experiencing hypothyroidism at the cellular level. 

Whatsmore, as explained above, even if TSH and Free T4 are within the normal range, thyroid antibodies can make it harder to get (and stay!) pregnant.  

Autoimmune hypothyroidism is often a slowly progressing condition, meaning that you can have antibodies causing thyroid inflammation and sub-optimal function for years, before you notice any symptoms or before TSH or T4 lab values come back out of range. 

Without testing for thyroid autoantibodies, early stages of autoimmune conditions – and an underlying cause of your infertility – all get missed.

2. Sub-Optimal Levels Get Missed. 

The standard approach to thyroid testing catches overt thyroid disease, but misses the more subtle thyroid issues that can still cause infertility and increased risk of  miscarriage. 

The distinction between “normal” and “optimal” thyroid levels is crucial to understand. Many infertility issues occur when thyroid levels are “normal”, but sub-optimal. 

This means that, while you do not have a diagnosable thyroid disease, your thyroid hormone is not functioning optimally as needed to support healthy hormones, follicle development, conception and embryo growth. 

Identifying sub-optimal thyroid levels requires a more narrow reference range than what is used conventionally to determine “normal”. 

For example, reference ranges for TSH, often cited as 0.5 – 5.0mIU/L, are too broad, and based on population averages. For fertility and hormone health, an “optimal” TSH level is within a much more narrow range, between 1.0-2.5 mIU/L. 

Similarly, free T3 and free T4 levels may fall within the standard range, but may not be optimal for your specific metabolic or hormonal demands. 

3. Subclinical Hypothyroidism Gets Missed

Subclinical Hypothyroidism (SCH) is a milder form of thyroid dysfunction where serum thyroxine (T4) is in the normal range, and TSH is slightly elevated (often defined as TSH levels > 2.0 or 2.5 mIU/l)

SCH affects an estimated 5-10% of women of reproductive age, but those estimates jump to nearly 20% of women struggling with subfertility. 

While it may not cause overt symptoms, according to the American Society for Reproductive Medicine (ASRM), SCH is associated with an increased risk of infertility, miscarriage, and adverse pregnancy outcomes. 

Similarly, the American Thyroid Association (ATA) notes that women with SCH have a higher likelihood of miscarriage and preterm delivery. 

Ultimately, even a small disruption in thyroid function can interfere with the delicate hormonal balance needed to support ovulation, implantation, and early pregnancy. 

The standard approach to thyroid testing, with broad ranges based on population averages, and an incomplete panel, misses the small disruptions that could be causing fertility problems. 

Functional Thyroid Testing

Functional medicine testing differs from conventional approaches by offering a more comprehensive, in-depth, and individualized evaluation of thyroid health. 

While conventional testing typically focuses on TSH and sometimes free T4, functional medicine includes a full thyroid panel— and related nutrients like iodine, selenium, and vitamin D, that are all needed for optimal thyroid health. 

This broader scope can uncover subtle thyroid imbalances and pinpoint where to optimize thyroid function.

Here is the list of labs typically ordered by a functional provider, needed to accurately and thoroughly assess thyroid function.

Recommended thyroid tests for fertility:

• Thyroid-Stimulating Hormone (TSH): Assesses how well the thyroid is being signaled by the pituitary gland in the brain.
• Free T4 (Thyroxine): Measures the unbound, active form of T4, the thyroid hormone produced in the largest amount by the thyroid gland.
• Free T3 (Triiodothyronine): Measures the unbound, active form of T3, the hormone responsible for metabolic activity.
• Total T4: Provides an overview of the total amount of T4 in the blood, including both bound and free forms.
• Total T3: Measures the total amount of T3, both bound and free, to assess overall T3 production.
• Reverse T3 (rT3): Although inactive, rT3  is extremely helpful for understanding not just if thyroid levels are off, but also WHY, and what’s causing the issue. If rT3 is elevated, it suggests that stress is impacting your thyroid function. 
  
  

Thyroid Autoantibodies:

• Thyroid Peroxidase Antibodies (TPO-Ab): Identifies autoimmune activity commonly seen in Hashimoto’s thyroiditis and sometimes in Graves’ disease.
• Thyroglobulin Antibodies (Tg-Ab): Helps detect autoimmune thyroid conditions, particularly Hashimoto’s.
• Thyroid-Stimulating Immunoglobulin (TSI): Used to confirm Graves’ disease, as it stimulates excess thyroid hormone production.
  
  

When to Seek Help from a Specialist

Knowing when to seek help from a specialist for thyroid issues is crucial, especially if you’re experiencing symptoms that impact your daily life or fertility. 

When to see an endocrinologist: 

You should consider seeing an endocrinologist if you have persistent symptoms like weight changes, irregular menstrual cycles, or hair thinning, despite normal thyroid blood tests. 

Additionally, elevated thyroid antibodies, a family history of autoimmune thyroid disease, or difficulty managing thyroid hormone levels warrant further evaluation by a specialist. 

Unfortunately, while endocrinologists can help identify anatomical/physical causes of thyroid dysfunction, and manage thyroid levels with prescription drugs, they’re not trained in getting to the root cause of the issue. 

If your conventional doctor leaves you still wondering WHY your thyroid isn’t operating optimally, and what you can do about it so you’re not stuck taking medications for the rest of your life, it’s time to see a functional medicine provider. 

When to see a functional medicine provider: 

Working with a provider trained in functional medicine can be invaluable for understanding the root cause of your thyroid and fertility struggles, and healing the underlying issue. 

A provider trained in functional medicine can help you implement evidence-based strategies for nutrition, stress management, and exercise, all of which are critical for supporting thyroid health. Learn more. 

Supporting Your Thyroid Naturally

For most thyroid issues, you can support thyroid healing with a holistic approach. By focusing on nutrient-rich foods, managing stress, and prioritizing exercise and sleep, you can support your thyroid naturally. 

These natural approaches are not mutually exclusive with medical management. Nutrition and lifestyle approaches to thyroid health and improve the efficacy of thyroid hormone replacement, and help you take a lower dose.  

Whether or not you choose to support your thyroid levels with prescription drugs, your thyroid function (and fertility!) will benefit from also including natural, diet and lifestyle treatments.

 

Take Home: 

If you’ve been struggling with infertility – whether to get pregnant or to stay pregnant – looking into your thyroid health is essential to get the answers you need. 

Both hypothyroidism and hyperthyroidism can disrupt ovulation, hormone balance, and implantation, making it harder to get and stay pregnant. 

Unfortunately, many conventional doctors only test TSH during a fertility workup, missing key factors like free T3, free T4, reverse T3, and thyroid antibodies that could reveal underlying thyroid dysfunction. 

Subclinical hypothyroidism, elevated thyroid antibodies (like TPO-Ab), or poor T4-to-T3 conversion may go undiagnosed, even if your TSH is “normal.” 

If you suspect your thyroid could be affecting your fertility, advocating for a comprehensive thyroid panel and working with a fertility-focused functional practitioner can help uncover hidden imbalances and support your journey to a healthy pregnancy.