Thyroid imbalances and fertility: A crash course

We hear a lot about estrogen and progesterone when it comes to fertility and pregnancy, but what about our thyroid hormones?

The American Thyroid Association estimates 20 million Americans have some form of thyroid disorder, yet up to 60% of those afflicted are unaware.

The thyroid is a butterfly-shaped gland located at the base of the neck. It is regulated by the hypothalamic-pituitary adrenal (HPA) axis, the same network that interacts with and regulates reproductive function.

The pituitary secretes thyroid stimulating hormone (TSH), which signals the thyroid to secrete hormones, T3 and T4. These hormones are responsible for regulating metabolism, growth, body temperature, and energy.

These hormones can also have an impact on our reproductive hormonal health, and more specifically, fertility. Read on if you’re wondering:

• What is the difference between hypothyroidism, hyperthyroidism, and thyroid autoimmunity?
• How does our thyroid impact our menstrual cycles?
• How does our thyroid impact fertility?
• Does hypothyroidism or Hashimoto’s increase risk for miscarriage?
• What are the optimal levels of T3, T4, and TSH if I am trying to get pregnant?
• How do I know if it’s time to see a doctor for my thyroid?

An intro to thyroid disorders and fertility: what role does our thyroid play in infertility?

1 in 8 women will develop a thyroid disorder in her lifetime. Both an under-active and overactive thyroid can have a negative influence on sex hormone metabolism, ovulation, implantation, and embryonic development.

However, different symptoms and challenges will arise depending on the type of thyroid disorder you have. Let’s take a look at the main types of thyroid issues:

Hypothyroidism

Hypothyroidism is an under-active thyroid and occurs in 2-4% of reproductive aged women. Symptoms include fatigue, weight gain, hair loss, dry skin, intolerance to cold, constipation, and depression.

More than 50% of hypothyroid patients have abnormal menstrual cycles, including heavy or infrequent periods. Hypothyroidism has been linked to elevated prolactin, a hormone that affects fertility by inhibiting FSH and LH, two hormones responsible for triggering ovulation. Without ovulation, fertilization of the egg cannot occur. Additionally, one study found incidence of miscarriage to be 6-15% in women with hypothyroidism, compared to 2.2% in those without.

Hyperthyroidism

Hyperthyroidism, or an overactive thyroid, causes symptoms such as  rapid heart rate, weight loss, tremors, nervousness, loose stools and insomnia.

Hyperthyroidism occurs in 2.3% of women struggling with infertility, compared to 1.5% of the general population. The change in sex hormones seen with hyperthyroidism results in scanty periods and shortened menstrual cycles (less than 21 days), impacting the ability to conceive. Despite these hormonal changes, ovulation is not found to be affected. Untreated hyperthyroidism is also associated with preterm delivery and delayed fetal growth.

Thyroid autoimmunity

Thyroid autoimmunity affects 5-20% of reproductive age women. Hashimoto’s and Graves’ disease are two examples in which the body creates antibodies that attack the thyroid.

In women with elevated antibodies, pregnancy rate is lower and miscarriage risk is 4x higher. The presence of these antibodies has been found to negatively impact fertility, even when thyroid hormones are within normal range.

What should my thyroid levels be to get pregnant?

There are several key hormones  that can help indicate if our thyroid is functioning properly or if something is awry. The major players we’ll be addressing today are T3, T4, and TSH.

Thyroxine (also known as tetraiodothyronine, or T4) is most readily produced by our thyroid gland. However, T4 actually has a minimal impact on regulating our metabolism.

Our liver converts T4 to T3, or triiodothyronine which is a more powerful regulator. If we are suffering from illness or other imbalances, our liver sometimes does not convert enough T4 to T3, which can subsequently have an adverse impact on our metabolic rate.

A majority of the T4 and T3 hormones in our blood have bound themselves to thyroxine-binding globulin, which is a protein that helps transport thyroid hormones to our body’s tissues to stimulate them to produce proteins and increasing the amount of oxygen that these cells use. A small amount of T3 and T4 continue to circulate freely in our bloodstream; these are active hormones that are referred to as “free" T3 and T4.

Understanding the distinction between free T3 and T4 and the “total” hormone levels, which include the bound forms, is important. Many blood tests will only report the “total” T3 and T4 levels, which can be misleading if there are high amounts of bound T3 and T4 circulating in your bloodstream. For that reason, if you are experiencing symptoms of a thyroid imbalance it is recommended that you test for both “free” T3 and T4 as well as total levels.

Another way thyroid dysfunction is diagnosed by measuring thyroid stimulating hormone (TSH) in the blood. TSH is produced by our body’s pituitary gland, another endocrine system star that plays a major role in regulating bodily functions.

Levels of TSH and our T3 and T4 hormones are inversely related. If thyroid levels are too low (i.e., if we have an under-active thyroid), our pituitary will pump out higher levels of TSH to encourage our thyroid to increase production. Conversely, if we have an overactive thyroid and levels are too high,TSH levels will be low because our pituitary will not want to stimulate more production.

The reference range of TSH varies from 0.5-4.5mIU/L, with high TSH being an indicator of hypothyroidism, and low TSH an indicator of hyperthyroidism. Many studies have shown a TSH less than 2.5mIU/L has been most effective in addressing fertility related to thyroid dysfunction.

When should I see a hormonal health specialist for thyroid issues?

The American Thyroid Association recommends screening for thyroid dysfunction starting at age 35 in non-pregnant adults. However, if you are wanting to conceive and having trouble, you should consider seeing your doctor sooner for further work-up.

Below are some signs that your thyroid may be the culprit behind your issues conceiving:

• Family history of thyroid disease
• Irregular menses
• History of two or more miscarriages
• Unable to conceive after one year of unprotected intercourse

Once a thyroid disorder is diagnosed, treatment can vary depending on severity of symptoms. Treatment may include dietary modifications, nutritional or herbal supplements, and pharmaceutical intervention.

And remember, thyroid issues are manageable. And knowledge is power: symptoms of thyroid dysfunction, including infertility, are expected to resolve with proper treatment. One study of 294 infertile women found that 23.9% were hypothyroid. After being treated for hypothyroidism, 76.6% of infertile women were able to conceive within one year.

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