Thyroid and Fertility
Thyroid problems are extremely common, and because they can be asymptomatic, it can be difficult to know if a condition is present. The thyroid is absolutely essential for healthy fertility. Dysfunction can cause ovulatory disorders, menstrual irregularity, and recurrent miscarriage. The thyroid gland is key to support ovarian function. If thyroid function is low, the eggs will not mature fully and, ovulation can be either delayed or prevented. Surprisingly, 5-20 percent of women in their reproductive years have a thyroid condition.
Autoimmune thyroid disease is one major cause of many thyroid conditions. Women who test positive for thyroid antibodies will generally develop hypothyroidism at a rate of 20% per year. Often times, when a fertility general health screening is done, the only test completed for the thyroid is TSH (Thyroid Stimulating Hormone). TSH is a useful test to screen for hypo or hyperthyroidism, however it does not detect autoimmune conditions. Autoimmune thyroid antibodies can be present with no symptoms of hypothyroidism at all. In autoimmune thyroiditis, TSH levels are often normal so it is important to complete a full thyroid panel. This can determine if there is a risk of developing hypothyroidism which could threaten a pregnancy. When a woman becomes pregnant, there are widespread hormonal changes in the body, including an increased demand for thyroid function. If autoimmune antibodies are present, this can trigger miscarriage due to inability of the thyroid to compensate normally for pregnancy. Many cases of recurrent miscarriage or premature birth are related to thyroid disease so this is a very important part of fertility screening in those who suffer from miscarriages. One of the protective functions of pregnancy is a decrease in immunity, so it is unlikely that a new flare up of Grave’s disease (an autoimmune disease which causes symptoms of hyperthyroidism and goitre) will occur during pregnancy, however often we see worsening of hypothyroidism.
Another condition which can be present in those with thyroid disease is primary ovarian failure. This is caused by autoantibodies to the ovary and is associated with autoantibodies to the thyroid. This condition, although not common, can be devastating for women.
In men, hypo- or hyper- thyroidism can cause poor development of sperm, so for all men with sperm quality concerns, the thyroid should be screened. Although thyroid disease is more common in women, it can still happen for many men and go undetected.
Symptoms of Hypothyroidism:
Symptoms of Hyperthyroidism:
To Optimize Fertility the Following lab Testing for Thyroid Should be Done
Explanation of thyroid lab values and normal ranges are included.
This is a hormone released by the pituitary gland(in the brain) which stimulates the thyroid to release thyroid hormones. It is controlled by feedback mechanisms, when thyroid hormone is low in the bloodstream, the pituitary gland will increase its output of TSH to stimulate more release of thyroid hormones.
Normal Levels : 0.4 – 3 mIU/L. Although this range is more commonly accepted, data from the National Academy of Clinical Biochemistry suggests that 95% of the population has a TSH below 2.5 mIU/L.
If levels are above 2, and especially if thyroid antibodies are present with signs and symptoms of hypothyroidism, this is suspect of “subclinical hypothyroidism” and may present risks for fertility. In Canada, labs and many physicians are still using the “old” ranges of up to 5.0 mIU/L, however many patients do experience symptoms of hypothyroidism between 3-5 mIU/L. For fertility and pregnancy we aim for below 2 mIU/L.
A thyroid hormone produced by the thyroid gland. This is the most abundant thyroid hormone in the body. It is also the weaker of the thyroid hormones. It represents 80% of the thyroid hormones in the body, and its major function is to be converted into the stronger T3 hormone. This is a measure of the T4 which is not bound to carrier proteins. Although the range for free T4 is wide, many patients feel best (and may have better fertility) with this number in the upper 1/3 of the range.
Normal Levels: 10-23 pmol/L
A thyroid hormone produced from the conversion of T4 by enzymes. This is a much stronger thyroid hormone and has powerful effects on the body’s metabolism. It represents 20% of the total thyroid hormones in the body. The conversion of T4 into T3 can also be impaired, so this is important to investigate. This is a measure of the T3 which is not bound to carrier proteins. Many patients feel best with their free T3 in the upper 1/4 of the range.
Normal Levels: 3.5 – 6.5 pmol/L
Optimally, the thyroid gland produces T4 and T3 in an approximately 4:1 ratio.
When there is sufficient T3, the body will convert excess T4 into a compound known as reverse T3. This compound is inactive, and serves to protect the body from excessive overstimulation by thyroid hormone. It can bind to receptors where T3 would normally bind, however it does not stimulate the receptor as T3 would. In some cases, the body may actually convert T4 excessively into reverse T3, which can result in metabolic abnormalities. This condition should be screened for whenever signs and symptoms (including low body temperature) are present in fertility patients.
Normal Levels: 200-300 pmol/L
These are antibodies against an enzyme known as Thyroid Peroxidase. Thyroid peroxidase is involved in the conversion of T4 to T3. If antibodies exist, this can cause a conversion disorder which results in hypothyroidism.
Normal Levels: <35
These are antibodies directed against a protein known as Thyroglobulin. Thyroglobulin is present in the thyroid gland and is essential for the production of thyroid hormones. These antibodies can trigger destruction of the thyroid gland.
Normal Levels: <20
Treatment for thyroid conditions can involve thyroid hormones, nutritional supplements, amino acids and herbal medicines, depending on which type of thyroid condition is present. Naturopathic treatment for thyroid is often integrated with conventional thyroid medications when needed to optimize response for fertility concerns.
- Mosby’s Manual of Diagnostic and Laboratory Tests