Illustration of woman showing the thyroid gland and hypothyroidism/under active thyroid
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What is Hypothyroidism?

Jen on the roof terrace at Natural Cycles headquarters.

Written by Jennifer Gray

Jennifer Gray

Jennifer Gray is an award-winning writer with more than five years’ experience covering reproductive topics ranging from birth control to planning pregnancy. She is passionate about providing women with accurate information grounded in science they can use to take charge of their own health - while also dispelling myths that exist within the field of women’s health. She holds a Master of Science from the University of Edinburgh and currently lives in Ireland.

Medically reviewed by Jack Pearson, Medical Affairs Manager at Natural Cycles

Jack Pearson

Dr. Jack Pearson is a previously HCPC registered Embryologist with a PhD in reproductive medicine. Prior to joining Natural Cycles leading Medical Affairs, he worked for more than 10 years in a clinical setting working at some of the busiest fertility clinics in the UK. Today he spends most of his time working with experts at the world’s leading institutions to carry out important research with the vision to further the field of female health. He earned his PhD from the University of Sheffield specializing in Sperm Metabolism and currently lives in London.

An underactive thyroid or hypothyroidism is a condition where an insufficient amount of the thyroxine hormone is produced in the thyroid gland. Hypothyroidism affects both men and women, but is more common in women and is also linked to the menstrual cycle and female fertility more generally. In this article, we’ll look at the causes of hypothyroidism, symptoms, treatments, and more.

What is the thyroid gland?

Found in the lower front of the neck, the thyroid gland is a butterfly-shaped organ that’s main function is to make the thyroid hormone which is then carried through the blood to various tissues throughout the body. The thyroid hormone has many functions including regulating the body’s temperature and ensuring that our muscles and organs work as they should.

Symptoms of hypothyroidism

Although the majority of cases are mild, it’s estimated that 5% of the US population is affected by hypothyroidism. In many cases, an underactive thyroid can take years to develop and symptoms of hypothyroidism are not always obvious at first. 

The most common symptoms of hypothyroidism include:

  • Weight gain
  • Tiredness
  • Depression
  • Feeling cold
  • Dry skin and/or hair

If you are concerned that you might have an underactive thyroid, you should speak to your doctor who may carry out blood tests and a physical exam. In women, thyroid conditions are more likely to occur after pregnancy or menopause. 

Hypothyroidism causes

There are a number of different causes of hypothyroidism. We’ve broken these down below:

Autoimmune disease - this is more common in women than men and can happen suddenly, or develop over several years. This happens when the immune system (which normally works to protect the body from infection) mistakenly attacks the thyroid. This stops the production of the thyroid hormone, causing an underactive thyroid.

Surgery - if part of the thyroid gland has been surgically removed, this can impact the production of the thyroid hormone too. If the whole thyroid gland has been taken out, this will lead to hypothyroidism as the gland will be unable to produce its own thyroid hormone.

Radiation - in some cases, radioactive iodine is used to destroy the thyroid gland, this is a method for treating thyroid cancer, for example. This method can cause hypothyroidism by impairing thyroid function.

Congenital hypothyroidism - occasionally babies are born without a thyroid gland, with the gland in the wrong place or with enzymes and cells in the thyroid that don’t function properly. In these cases the individual is likely to experience thyroid problems from birth. Babies are usually screened for congenital hypothyroidism when they are a few days old.

Thyroiditis - this is an inflammation of the thyroid gland. Thyroiditis can initially cause hyperthyroidism as the thyroid gland unloads its full supply of the thyroid hormone into the bloodstream. This is followed by hypothyroidism, as there is a shortage of the hormone.

Medicines - some medication can also impair thyroid function. Hypothyroidism through medication is more likely to happen when a person has a genetic tendency to autoimmune thyroid disease in the first place.

Too much/too little iodine - the thyroid gland needs iodine to make the thyroid hormone. Iodine is part of our diet, but too much or too little of it can affect the thyroid gland and cause hypothyroidism.

Damaged pituitary gland - located in the brain, the pituitary gland is responsible for regulating hormones throughout the body. Damage to the gland can have a knock-on effect and impair thyroid function.

Rare disorders - in very few cases there are certain conditions that interfere with the thyroid gland and cause hypothyroidism.

Hypothyroidism treatment

If you are concerned about hypothyroidism, or are suffering from any of the symptoms associated with the condition, it’s always a good idea to speak to a healthcare professional. A prescription for thyroxine replacement can be given if you are diagnosed with hypothyroidism - this synthetic version of the hormone works in the same way as natural thyroxine hormone to regulate body function.

Many people with hypothyroidism may have to take hormone replacement medication for the rest of their lives, but with treatment most symptoms are manageable and many women and men with thyroid conditions can continue to live healthy lives.

Hypothyroidism and the menstrual cycle

In women, there is a link between fertility and thyroid conditions and an underactive thyroid is more likely to develop after menopause or post-pregnancy. Hypothyroidism can also affect the menstrual cycle and cause heavy, late, or irregular periods. An underactive thyroid can also have more subtle effects on your cycle. For example, since the thyroid is responsible for regulating body temperature, it can also make it more difficult to detect the natural rise in body temperature that happens after ovulation occurs.

Measuring basal body temperature (BBT) in order to determine fertility is a form of natural family planning. While traditional BBT methods require manual calculation and charting, the Natural Cycles app uses an algorithm to find and predict your fertile window. Women with hypothyroidism, who use Natural Cycles as birth control, won’t find it any less effective as a method. However, it’s worth knowing that if it is more difficult to detect ovulation, the algorithm could give more red days during the cycle. Red days are days when you could be fertile and therefore should use protection or abstain from sex if you are preventing pregnancy.

Pregnancy and hypothyroidism

As mentioned, hypothyroidism is more likely to develop post-pregnancy. However, for some women, it can make conceiving difficult in the first place. This is due to the hormonal imbalance caused by an underactive thyroid which can delay or stop ovulation. Ovulation is essential in order for an egg cell to be released and ready to be fertilized by a sperm cell. 

Learn your cycle, know your body better

Tracking the signs and symptoms that occur throughout your menstrual cycle can provide really useful insights into the way your body is behaving. Whether your cycle is affected by stress, is naturally getting shorter as you get older, or you’re experiencing more severe PMS symptoms, there is a lot that can go unnoticed if we don’t pay attention to our cycle. 

Natural Cycles is not only a certified birth control method, but it can also be used to plan a pregnancy… What’s more, is that the app offers emotion, pain, and other symptom tracking functionality, so you can keep on top of any changes you notice in your body.

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