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  • Dr. Singh, ND

Thyroid Auto-Immune Testing for Unexplained Infertility

In general, dealing with Infertility has many challenges, and it can contribute to significant stress, anxiety, and depression. What can make a difficult situation even more difficult? Not knowing exactly what it is that is causing the fertility issues. "Unexplained Infertility" is a common and rather frustrating diagnosis. It is the equivalent of basically telling someone that there is no explanation of why they are going through significant hardship. It also leaves patients feeling like they have less power over the situation. If they were aware of what was actually causing the infertility, then they may be able to take more action against it.

In my opinion, as research continues to focus on unexplained infertility, we will later have a better understanding of why a portion of the population might be experiencing unexplained infertility. Thyroid conditions and testing may hold the answer for a subpopulation of those diagnosed with unexplained infertility.

Three main hormones are tested to evaluate for thyroid health: thyroid-stimulating hormone (TSH), Triiodotyrosine (T3) and thyroxine (T4).

Three important categories of thyroid conditions:

1. Overt Hypothyroidism: A clear and well-established diagnosis of Hypothyroidism based on hormone parameters (TSH is above 5.0 mIU/L).

2. Subclinical Hypothyroidism: the patient does not have any symptoms suggestive of hypothyroidism, but on lab testing the TSH is above 4.5-5.0 mIU/L with normal T4 levels in the body.

3. Elevated Auto-Immune Thyroid Antibodies: the body is producing antibodies that attack an enzyme in the thyroid gland, Thyroid Peroxidase (TPO), or Thyroglobulin (TGab) which is the carrier of thyroid hormones in the body.

How does this affect Fertility?

It has been established that poor functioning of the thyroid gland is strongly connected to infertility, increased miscarriage rates, and possibly decreased developmental outcomes in the baby. Overt hypothyroidism has been clearly connected to the above mentioned outcomes, so a Woman with elevated TSH is usually treated with synthroid (synthetic T4 hormone).

Subclinical Hypothyroidism is more of a grey area. The levels of TSH that are being used as a cut-off to determine optimal functioning of the thyroid gland are not well established. When a Woman is pregnant, the rising estrogen levels in the body interfere with normal thyroid function and TSH increases. Current guidelines suggest a TSH of 2.5 of less during the 1st trimester, 3.0 or less during the 2nd trimester, and 3.5 or less during the 3rd trimester. The current controversy is whether or not Women experiencing unexplained infertility should have a TSH below 2.5, or if a TSH above 2.5 is associated with infertility.

Based on a published review on the topic, there is only an observed improvement in pregnancy rates and decrease in miscarriage rates when TSH is kept below 4.0 mIU/L for Women trying to conceive. A TSH above 4.0 for Women trying to conceive may contribute to increased infertility and miscarriage rates.

Thyroid Auto-Immune Antibodies:

This where the cut-offs for "subclinical hypothyroidism" become a bit more blurry. In Women who have elevated levels of Thyroid Peroxidase Antibodies (TPO-Ab) there is good evidence to suggest that miscarriage rates increase significantly and fair evidence to support that infertility rates increase as well. In fact, some studies have shown increased rates of infertility for Women with elevated TPO-Abs, even when all other thyroid hormone levels are perfectly normal.

Women who had both elevated TPO-Abs and a TSH above 2.5 mIU/L were shown to have increased pregnancy rates when treated with synthroid. However, Thyroid Peroxidase Antibodies are not a test that is done in a routine check-up nor fertility evaluations. It may however, for Women experiencing unexplained infertility, provide more insight as to the cause of the unexplained infertility. Discussing with your healthcare providers the benefit of testing for thyroid antibodies may prove helpful for this subpopulation of patients.

This article is in no way a replacement for medical advice or medical care, it is advised that anyone concerned about their Health should speak with their Naturopathic Doctor or Primary Care Provider.


1. Subclinical hypothyroidism in the infertile female population: a guideline. (2015). Fertility and Sterility, 104(3), 545-553.

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