LH is a pituitary hormone that triggers ovulation and stimulates the ovaries to make hormones.

What LH does

LH (luteinising hormone) is released by the pituitary gland, a small gland at the base of the brain. Across the menstrual cycle, LH works together with other hormones such as FSH to control how follicles develop inside the ovaries. In the middle of the cycle, an LH surge triggers the release of an egg, which is the process of ovulation. After ovulation, LH also helps support the next phase of the cycle. In addition, LH stimulates the ovaries to produce hormones, including small amounts of androgens. Because of these roles, LH levels change naturally depending on the point in the cycle.

Some women with PCOS have a higher LH level or a raised LH to FSH ratio. This pattern can contribute to irregular ovulation, which is one feature of PCOS. It can also relate to higher androgen signs in some people, such as acne or excess hair growth. However, this pattern is not present in everyone with PCOS, and it is only part of a wider picture. You can read more about this picture on the hormones and PCOS symptoms pages.

Can the LH/FSH ratio confirm PCOS

No. The LH/FSH ratio is only one clue and not a stand-alone test for PCOS. It is not raised in every patient, so a normal value does not rule PCOS out, and a high value does not confirm it on its own. These hormone levels shift across the phases of the menstrual cycle, so the timing of the test matters and results can differ from one day to another. A doctor considers the result in the context of symptoms, cycle pattern, other hormones, and sometimes ultrasound before drawing any conclusion.

What it means for you

If a doctor measures your LH, it is usually part of a wider picture rather than a value that stands alone. Understanding this can ease worry when you see a single test result that looks unusual. If you have irregular periods or concerns about fertility, it is worth talking to a doctor or pharmacist. They can help explain what your results mean in your own context. For the basics, see also what is PCOS.

This glossary is education, not diagnosis. For your own situation, ask a doctor or pharmacist.