Thyroid-Stimulating Hormone (TSH)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 7, 2026

Thyroid-stimulating hormone (TSH) is secreted by the anterior pituitary gland and drives the thyroid gland to produce thyroxine (T4) and triiodothyronine (T3). When thyroid output falls, TSH rises. When output is high, TSH falls. It is the primary clinical marker for thyroid function.

Standard laboratory reference ranges for TSH span roughly 0.5 to 4.5 mIU/L. "Within normal limits" is not the same as "optimal for reproduction." Research published in the Journal of Clinical Endocrinology and Metabolism found that higher TSH levels within the standard normal range were independently associated with unexplained infertility.⁶⁸ For women trying to conceive, many RRM clinicians target a TSH below 2.5 mIU/L, because subclinical hypothyroidism at higher values within the standard range carries documented risk for anovulation, luteal phase insufficiency, and miscarriage.

The practical implication: a TSH of 3.8 mIU/L may not trigger treatment from a general practitioner. An RRM clinician may read that same value as a contributor to cycle dysfunction and act on it.

TSH should be evaluated alongside free T4, free T3, and thyroid antibody levels when reproductive concerns are present. Autoimmune thyroid disease can affect fertility even when TSH remains near-normal.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.