Can hypothyroidism cause infertility?

Apr 28, 2021

Can hypothyroidism cause infertility?

Thyroid disorders, thyroid antibodies, and suboptimal thyroid function are often missed during fertility evaluation because of the way it’s tested. Yet, thyroid disorders are much more common than you think, especially if you’re struggling with low anti-Müllerian hormone (AMH), high follicle-stimulating hormones (FSH), and premature ovarian failure/insufficiency

While 2 – 4% of women of reproductive age have hypothyroidism, up to 24% among women with infertility are hypothyroid. A clinical study found that once they received treatment for hypothyroidism, 76.6% of them conceived within six weeks to 1 year [1]. Therefore, if you have been struggling with infertility, optimizing thyroid function could be the key step to conception. 

This article will cover:

  • how thyroid function affects your fertility
  • how to know if you have low thyroid function
  • the treatment options available for hypothyroidism
  • ways to balance your thyroid hormones naturally to increase your chance of getting pregnant

The roles of thyroid hormones and fertility

The thyroid is the master gland of metabolism in your body—the thyroid hormones activate the mitochondria and metabolism genes. Healthy thyroid function is critical for sex hormone production, and the development of eggs and uterine lining that you need in order to have healthy cycles and become pregnant. 

During pregnancy, you need even more thyroid function for placental and fetal development. Thyroid disorders and antibodies can cause miscarriage or other pregnancy complications.

Thyroid dysfunction can result in [1,2]:

  • Anovulatory cycles
  • Menstrual irregularities or heavy bleeding
  • Low libido
  • Luteal phase defects
  • High prolactin
  • Sex hormone imbalances
  • Reduced DHEA, which may cause hormone imbalances and low sex hormone levels [3]
  • Failure to sustain a fertilized egg
  • Low antral follicle count (AFC)
  • Low anti-Müllerian hormone (AMH), a measure of ovarian reserve
  • High follicle-stimulating hormone (FSH)
  • Early pregnancy loss (<20 weeks)

Among women over 35, subclinical hypothyroidism is associated with lower ovarian reserve and markers of lower fertility, including low AMH and elevated FSH. Among those under 35 years old, subclinical hypothyroidism is associated with higher FSH but not AMH or AFC [4]. 

Thyroid antibodies are also associated with:

  • Diminished ovarian reserve (DOR), which corresponds to elevated but not menopausal basal FSH levels, low AMH, and AFC. DOR naturally happens in the mid-40s, but when it can be problematic if it happens sooner [5,6].
  • Premature ovarian failure, also called primary ovarian insufficiency (POI), is defined by postmenopausal levels of FSH (>40 IU/L), and four or more months without cycles at the age of under 40 years old [5,7]. 

Do you have low thyroid function?

Aside from infertility and menstrual issues, symptoms of hypothyroidism may include:

  • Fatigue despite getting enough sleep
  • Brain fog
  • Low mood, irritability, and depression
  • Weight gain or inability to lose weight despite diet and exercise, although it’s possible to be hypothyroid at a healthy weight
  • Feeling cold, especially in the extremities
  • Low basal body temperature (<97.8 degrees F or 36.5 degrees celcius
  • Brittle hair and nails
  • Aches, pain, and weakness in the body
  • Slow movements and thoughts

Hypothyroidism may also contribute to polycystic ovarian syndrome, obesity, metabolic syndrome, elevated cholesterol, heart disease, and other health issues [8]. These issues make it harder to become pregnant and increase the risk of pregnancy complications. 

Overall, optimizing your thyroid function will not only improve your fertility, but also your overall health and well-being. 

Thyroid lab tests for fertility

To check your thyroid function, your doctor will typically test only for thyroid-stimulating hormone (TSH), and occasionally total T4 and free T3. 

Elevated TSH is a good screening test for hypothyroidism, while low TSH may indicate hyperthyroidism. The higher TSH is, the lower your thyroid function. However, testing these alone may miss subclinical hypothyroidism, which can also contribute to infertility.

Most medical lab tests have a TSH cutoff for “normal” thyroid function at around 4 – 5 mIU/L. When TSH is above this level, your doctor will prescribe thyroid hormone replacement, mainly levothyroxine (T4). However, some people feel better with cytomel (T3), a combination of T3 and T4, or a bioidentical thyroid hormone such as Armor. 

Studies have shown that TSH of under 2.5 is best for reproductive outcomes. Therefore, the American Thyroid Association recommends titrating thyroid doses until TSH falls under 2.5 [9]. However, some doctors may not initiate treatment until the TSH rises above 5 or 10 mIU/L. 

Many thyroid patients continue to experience thyroid symptoms even with standard treatments until they start addressing the lifestyle factors that impair thyroid function. 

Testing a full thyroid panel allows you to see where the dysfunctions are within the thyroid axis, even if TSH, T4, and T3 come back normal. The full thyroid panel tests for:

  • TSH measures a pituitary hormone that reflects thyroid function
  • Free T4 measures unbound T4, the less active hormone
  • Total T4, which is the total output of your thyroid gland
  • Free T3 measures unbound T3, the active thyroid hormone
  • Total T3 measures the total converted thyroid hormone
  • Thyroxine-binding globulin, a protein that binds thyroid hormone and help transport them through the blood
  • Thyroperoxidase antibodies (TPO-Ab), the most common thyroid antibody
  • Thyroglobulin antibodies (Tg-Ab), another antibody that is often found in hypothyroidism
  • TSH receptor antibodies (TSHR-Ab), an antibody associated with Graves’ disease or hyperthyroidism
  • T3 resin uptake, an estimate of thyroxine-binding globulin in the blood
  • Reverse T3 (rT3), a mirror image of T3, which blocks thyroid hormone function

We’ll discuss a few potential lifestyle causes of thyroid dysfunction in the next section.

Causes of low thyroid function

Suboptimal thyroid function and hypothyroidism are typically due to problems outside of the thyroid gland. The thyroid axis shares the hypothalamus and pituitary with the gonad (sex hormone) and adrenal (stress hormone) axes. These three hormonal systems are deeply intertwined with each other. 

The connections between stress response (adrenals) and thyroid axes [10].


Stress tends to reduce thyroid and sex hormones (progesterone before estrogen), while increasing your stress hormones. The increased cortisol reduces thyroid conversion and increases reverse T3, a thyroid hormone that blocks the thyroid receptor and decreases thyroid function [10]. 

Nutrient deficiencies and gut health

More importantly, after your thyroid hormones produce T4, other tissues, including the gut, liver, and gut bacteria, activate your thyroid hormones by converting the less active form T4 into the active form T3 [11,12]. The conversion process requires nutrients including zinc, iron, iodide, and selenium [11].

Once T3 reaches its target cells, it also requires vitamin A and zinc to turn on the right genes. 

Autoimmunity and thyroid antibodies

Most cases of hypothyroidism in developed countries are due to the immune system attacking the thyroid gland. It is an autoimmune condition caused by an imbalanced immune system due to a combination of genetic predisposition, leaky gut, and lifestyle triggers [13]. 

15% of women with normal thyroid function (euthyroid) have thyroid antibodies[14]. While they don’t always become full-on hypothyroidism, these antibodies interfere with conception and pregnancy, contributing to infertility and miscarriages [15]. 

Gluten intolerance

Gluten is a sticky protein found in wheat, rye, and barley that gives bread its bouncy nature. Because of the protein structure, it is difficult to digest, leaving partially digested fragments that can trigger leaky gut through the zonulin pathway [16]. 

Gluten may also trigger autoimmunity because the gluten fragments are similar to many of our own tissues, including the thyroid [17]. A clinical study found that a gluten-free diet significantly reduced thyroid antibodies and increased thyroid hormone secretion in women with Hashimoto’s thyroiditis[18].

Estrogen dominance

High estrogen increases thyroxine-binding globulin, which can reduce the overall thyroid function [19].

Chronic inflammation

Chronic inflammation and many other illnesses can increase reverse T3, which blocks the thyroid receptors. The inflammation may also reduce free T3. Once the inflammation or illness is resolved, thyroid function typically normalizes [20].

How to increase thyroid hormone naturally for fertility

As you can see, numerous lifestyle factors affect your thyroid function. Therefore, to address thyroid issues and optimize thyroid function, you need to take a whole-body and whole-person approach. If the immune system has destroyed enough thyroid tissues, then thyroid hormone replacement is absolutely necessary and beneficial, but not always sufficient.

You should also further investigate and resolve the root causes to ensure optimal thyroid function and reduce thyroid antibodies, which will be necessary for conception and healthy pregnancy.

Natural ways to balance your thyroid hormones and manage thyroid antibodies include

  • Managing stress
  • Getting adequate nutrition
  • Addressing chronic inflammation 
  • Eliminating inflammatory foods such as gluten
  • Optimizing your gut and liver health 
  • Healing leaky gut
  • Optimizing your sleep 
  • Cutting out the thyroid disruptors, such as triclosan and fluoride

DHEA supplementation and thyroid-related fertility issues

Dehydroepiandrosterone (DHEA) is the most abundant steroid hormone in the body. It is a precursor to your sex hormones. Because the mitochondria (and thyroid) are important for steroid hormone production, low dehydroepiandrosterone (DHEA) is common among women who struggle with thyroid issues and fertility [3]. 

About 25% of women undergoing fertility treatments are prescribed DHEA supplements, especially if their tests show low DHEA levels [21]. A small clinical study of DHEA in women with thyroid antibodies found that DHEA reduced thyroid antibodies. Also, a combination of vitamin D and DHEA slightly reduced TSH levels, indicating improved thyroid function [22]. 

In our practice, we run a state-of-the-art test called the Dried Urine Test for Comprehensive Hormones along with full thyroid panels to guide hormone balancing and supplementation protocols. 


Many women become pregnant shortly after optimizing their thyroid function holistically after years of trying. Not only does balancing thyroid hormone improve your fertility, but it will also improve your overall health and quality of life.

If you would like to optimize your thyroid function naturally to maximize your fertility, book a free call with us here.


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