In simple terms: thyroid-stimulating hormone, a blood test that checks whether the thyroid gland is working normally.
Why it matters for PCOS
TSH is a hormone from the pituitary gland that tells the thyroid how much thyroid hormone to make. Thyroid problems such as an underactive thyroid can cause irregular periods, weight changes, fatigue, and mood changes, symptoms that overlap with PCOS. For this reason, guidelines recommend a TSH test to rule out a thyroid cause before PCOS is confirmed.
In general, a high TSH points to an underactive thyroid and a low TSH to an overactive one, but the result is always interpreted by a doctor alongside symptoms and other thyroid tests. TSH is not a measure of how severe PCOS is.
This glossary is education, not diagnosis. For your own situation, ask a doctor or pharmacist.