Thyroid-Stimulating Hormone (TSH)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 13, 2026

Thyroid-Stimulating Hormone (TSH) is secreted by the anterior pituitary gland and regulates the thyroid's output of thyroxine (T4) and triiodothyronine (T3). When thyroid hormone output falls, TSH rises. When output is excessive, TSH falls. It is the primary screening marker for thyroid dysfunction.

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." A cross-sectional study of 239 women found that those with unexplained infertility had significantly higher TSH levels than women whose infertility was attributable solely to severe male factor, even though all TSH values fell within the normal assay range.¹ That finding matters clinically: a TSH of 3.8 mIU/L may not prompt treatment from a general practitioner. An RRM clinician reads that same value as a potential contributor to cycle dysfunction.

For women attempting to conceive, many RRM clinicians target a TSH below 2.5 mIU/L. This threshold is grounded in evidence linking higher normal-range TSH to anovulation, luteal phase deficiency, and miscarriage risk.

TSH alone is not sufficient. Evaluation for reproductive thyroid dysfunction should include free T4, free T3, and thyroid antibodies. A Cochrane review found that subfertile women with euthyroid autoimmune thyroid disease may benefit from thyroxine replacement even when TSH is near-normal, though the evidence remained limited at the time of publication.² Autoimmune thyroid disease can impair fertility and increase miscarriage risk through mechanisms independent of TSH level.

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.