What is the role of the thyroid gland?

The thyroid gland produces hormones which regulate the body’s metabolic rate as well as heart and digestive function, muscle control, brain development and bone maintenance. The thyroid gland makes hormones that regulate the way the body uses energy. It is a butterfly-shaped gland that lies in front of your windpipe (trachea), just below your voice box (larynx). The thyroid gland uses iodine from food to make two thyroid hormones: thyroxine (T4) and triiodothyronine (T3).


How is the function of the thyroid gland controlled?

When thyroid hormone levels drop too low, the pituitary gland in the brain produces thyroid stimulating hormone (TSH). The thyroid responds to this by producing more hormones.


What are the symptoms of an Overactive thyroid?

Hyperthyroidism (an excess of thyroid hormones) affects up to five percent of women. Symptoms of this condition can include:

  • unexplained weight loss
  • increased appetite
  • feelings of nervousness and anxiety
  • difficulty sleeping
  • fewer or lighter menstrual cycles
  • increased sweating and heat intolerance.

How might this affect your fertility? In healthy, reproductive-aged women, luteinizing hormone (LH) peaks mid-cycle and signals the ovaries to release an egg. But when the body produces too many thyroid hormones, LH can remain elevated during the entire cycle. With these chronically increased levels of LH, the “peak” is not drastic enough to signal the ovaries to ovulate. In other words, it confuses the body. Unusual ovulatory function can often lead to irregular or absent menstrual cycles. Put simply, if you’re not ovulating, you can’t get pregnant naturally — your ovaries do not release an egg that can get fertilized by a sperm.


What are the symptoms of an Underactive thyroid?

Hypothyroidism (too little thyroid hormones) is found in two to four percent of women. Some common symptoms seen in hypothyroidism are:

  • weight gain
  • fatigue
  • constipation
  • feeling cold
  • thinning hair
  • pale skin
  • increased or heavier menstrual bleeding

When you have low levels of thyroid hormones, as you might have guessed, the body does not produce enough LH. Lower LH levels can inhibit that mid-cycle surge. As a result, your thyroid won’t signal to the ovaries that it’s time to release an egg. Without this signal, ovulation does not occur regularly, making conception difficult.


What is the commonest cause of an underactive thyroid gland?

Autoimmune disease. People who develop a particular inflammatory disorder known as Hashimoto’s thyroiditis have the most common cause of hypothyroidism (underactive thyroid). Autoimmune disorders occur when your immune system produces antibodies that attack your own tissues. The commonest antibodies against the thyroid gland are called anti-TPO antibodies. Some people can have these antibodies despite having apparently normal thyroid hormone levels and no symptoms.

Guide for patients having thyroid function tests

What are the normal levels of TSH?

A TSH level more than 4.5 mIU/L would indicate a degree a thyroid underactivity, even when patients do not have any symptoms; this condition is called subclinical hypothyroidism. For women interested in fertility, it is often suggested that the upper normal range of TSH might be as low as 2.5mIU/L.


What impact can the thyroid gland function have on fertility treatment outcomes?

A raised TSH or the presence of anti-TPO antibodies has been associated with worse pregnancy rates and increased miscarriage risk in some but not all of the studies assessing patients having IVF treatment.


What is the recommended treatment?

International medical guidelines advise the use of low-dose, hormone replacement with oral thyroxine tablets in patients with a TSH >2.5 and present anti-TPO antibodies and for all patients with a TSH>4.5. This treatment should ideally take place for 4-6weeks prior to commencing IVF treatment to allow for its effect to take place.


How long should I take thyroxine for?

We would advise you to continue with thyroxine during treatment and during pregnancy under the close supervision of an obstetrician and gynaecologist.

Thyroxine is safe in pregnancy and has been associated with improved outcomes in patients with an underactive thyroid.


What are the side-effects of using thyroxine tablets?

It is important to take thyroxine only at the doses advised by your doctor. The risk of developing side-effects with low-dose thyroxine is low. If you experience any of side effects such as rapid or irregular heartbeat, chest pain, shortness of breath, muscle weakness nervousness, change in appetite, weight loss, diarrhoea or vomiting, it’s important to discuss them with your doctor.


Who can I contact if I have any queries or concerns?

If you have any queries regarding your thyroid function, please do not hesitate to contact us on info@arkivf.co.uk to arrange a 1-to-1 consultation regarding this.