The LH to FSH ratio compares two of the most important pituitary hormones in reproductive health. LH (luteinising hormone) triggers ovulation and stimulates sex hormone production, while FSH (follicle stimulating hormone) drives follicle development and sperm production. In a normal menstrual cycle, FSH tends to be slightly higher than LH in the follicular phase, with LH surging dramatically at ovulation.
An elevated LH to FSH ratio — typically greater than 2:1 or 3:1 in the early follicular phase — is a classic finding in polycystic ovarian syndrome (PCOS). This ratio is not diagnostic on its own but forms part of the hormonal picture when evaluating irregular cycles, absent ovulation, and fertility concerns.
FAQs
Does an elevated LH/FSH ratio confirm PCOS?
Not on its own. The LH/FSH ratio is supportive of PCOS when elevated in the early follicular phase, but diagnosis requires the broader clinical picture. Current PCOS diagnostic criteria (Rotterdam criteria) include ovulatory dysfunction, androgen excess, and polycystic ovaries on ultrasound.
When should the LH/FSH ratio be tested?
The most informative time is in the early follicular phase (days 2-5 of the menstrual cycle), when the baseline LH and FSH levels are most reflective of the underlying pituitary regulatory pattern.
Can the LH/FSH ratio be normal in PCOS?
Yes. An elevated LH/FSH ratio is found in about 60-70% of women with PCOS, so a normal ratio does not exclude the diagnosis. Clinical symptoms, ultrasound findings, and androgen levels are important complementary diagnostic tools.
Does the ratio change with treatment?
Yes. Interventions that improve insulin resistance and reduce LH hypersecretion (exercise, weight loss, metformin) can normalise the LH/FSH ratio in PCOS over months, reflecting improvement in the underlying hormonal dysregulation.
