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  • Writer's pictureDr. H. Singh, ND

Uncovering the Impact of Thyroid Function on Infertility

Thyroid activity can impact health of various organ systems and its symptoms can be quite diverse. With respect to infertility, we are continually learning about the impact thyroid hormones have on likelihood of conception.

What does an elevated TSH mean?

TSH stands for thyroid stimulating hormone, and it is secreted by the pituitary gland in to the blood. From there, it reaches the thyroid gland and stimulates the production and release of thyroid hormones T3 and T4. If the body's levels of T3 and T4 decrease, then the TSH will go up, as the body tries to compensate by trying to stimulate more production of the thyroid hormones in the thyroid gland. Often, patients have the TSH tested and if it is above 4.0-4.5, they will be prescribed thyroid hormone to improve their chances of conception.

How do Thyroid Hormones Impact Fertility?

Thyroid hormones impact every level of fertility: from stimulating ovulation, supporting implantation, and supporting pregnancy. Poor thyroid function may impair one or all of these functions depending on the severity of the low-functioning thyroid gland. Elevated TSH levels have been shown to increase the risk of miscarriage and may increase the risk of infertility as well.

What is an Optimal TSH for Fertility?

The American Thyroid Association recommend treating a patient with thyroid hormones if the TSH is greater than or equal to 2.5 mIU/L. While this is debatable for natural conception, it is strongly recommended for patients going for assisted reproductive technologies (ARTs) as the increase in sex hormones during medicated cycles can further increase the TSH levels, pushing patients into subclinical hypothyroidism (where TSH is elevated but patient does not have any symptoms of hypothyroidism). This is especially true for patients that have elevated thyroid antibodies, as they maybe at greater risk for hypothyroidism with ARTs, such as IVF and/or IUI.

How much of an Impact does Thyroid Hormone have on Pregnancy Rates?

Research actually measuring increases in pregnancy rates are lacking for patients being treated with thyroid hormone compared to those who are not given thyroid hormone, particularly if they have subclinical hypothyroidism. A new research paper published in 2020 found that in a group of patients with elevated TSH that had been dealing with infertility for, on average, 5.8 years, 54% of them were able to conceive within 6 months of lowering the TSH to a level below 2.5 mIU/L with thyroid hormone treatment.

While the results from this study are promising, the sample size was small and lacked a control group. Each patient case should be evaluated to determine if thyroid hormone treatment is suitable based on patient's individual risks and potential benefits.

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. Please discuss with your healtcare provider and only make changes to your medications regimen if recommended by your doctor and under their guidance.


  1. Marghret, K., Wadhwa, L., & Arora, S. (2020). Evaluation of reproductive outcome in infertile hypothyroid women on thyroxine therapy. Journal of Human Reproductive Sciences, 13(4), 272.

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