Thyroid and Fertility
How your thyroid function may affect your fertility and chances of pregnancy
What is the Thyroid Gland and Why is it Important?
The thyroid gland is a small, butterfly-shaped gland located in the front of the neck, which is responsible for many important functions in the body, including metabolism, growth and bone mineralisation. There are several different hormones and molecules involved with thyroid function:
Thyroid-Stimulating Hormone (TSH): released by the pituitary gland in the brain to stimulate the thyroid to produce thyroid hormones
Thyroxine (T4): the non-active form of thyroid hormone. This is the form the thyroid gland actually secretes
Triiodothyronine (T3): The active form of thyroid hormone. T4 is converted into T3 after it has been secreted by the thyroid gland
Reverse T3 (rT3): an inactive form of T3 that is produced by the body during periods of stress
Thyroid antibodies: proteins created by the immune system that can damage the thyroid and contribute to autoimmune thyroid disease
The levels of thyroid hormones in the body need to be tightly controlled to maintain health. If the thyroid stops working properly and begins to produce fewer hormones in response to TSH, the brain will secrete more and more TSH in response, to keep thyroid hormone levels where they need to be. This means that when thyroid functioning is low, TSH levels increase. Many GPs will test only for TSH levels to assess for thyroid health, but this doesn’t give a complete picture. For example, if T4 is not being converted to T3, our health suffers, even if TSH levels are within the normal range. Likewise, if rT3 is too high, then TSH, T3 and T4 levels may actually appear normal on a blood test, even though the reality is poor thyroid function. If too many antibodies are being produced by the immune system, the thyroid gland is at risk of becoming damaged and losing function.
What is sub-clinical hypothyroidism and How Does it Impact Fertility?
Thyroid disorders, and particularly hypothyroidism, are a relatively common issue for women of reproductive age, affecting 2-4% of women in this group. Hypothyroidism is a condition where the thyroid does not produce enough thyroid hormones. This can negatively impact fertility by disrupting ovulation, leading to heavy or infrequent periods. But what happens when our thyroid becomes slightly less functional, without progressing to overt hypothyroidism? This is a condition called subclinical hypothyroidism (SCH). In SCH, TSH levels are elevated, although T3 and T4 levels are within the normal range. This means the pituitary gland is needing to work harder and produce more TSH than normal because the thyroid gland isn’t working as well as it should. SCH may be completely asymptomatic, however, there is also a risk that it may progress to clinical hypothyroidism in the future.
Subclinical Hypothyroidism and Fertility
Whilst the link between clinical hypothyroidism and infertility is well established, it’s less clear how SCH affects fertility, and if so, by how much. A 2020 study from researchers in America investigated the impact SCH can have on fertility. The study followed the IVF treatments of women with and without SCH and found that untreated SCH lead to significantly lower success rates with IVF. This is important because it demonstrates that even subclinical levels of thyroid dysfunction may have a significant impact on fertility for couples trying to conceive.
Pre-Screening with a Naturopath or Clinical Nutritionist to Support Your Fertility Journey
The issue of subclinical hypothyroidism and fertility shows why it is important to have a thorough pre-screening with a naturopath or clinical nutritionist before beginning your fertility journey. Naturopathic thyroid screenings test not only TSH but also look at T3, T4, rT3 and antibody levels, to give you a more accurate picture of your thyroid health. Naturopaths and clinical nutritionists can also assess your body’s levels of vital nutritional precursors required for healthy thyroid function, to help make sure you are supporting your body the best you can for your fertility journey.
