LH/FSH ratio
HormonesAlso known as: luteinizing to follicle stimulating ratio, LH to FSH ratio
The LH/FSH ratio compares levels of luteinizing hormone to follicle-stimulating hormone, both produced by the pituitary gland.
While FSH stimulates egg follicle development in the ovaries, LH triggers ovulation and supports progesterone production. The ratio between these hormones provides crucial insights into ovarian function and reproductive health that neither hormone alone can reveal.
Why this matters
The LH/FSH ratio is a powerful diagnostic tool for women's reproductive disorders. A ratio above 2.0 often indicates polycystic ovary syndrome (PCOS), where excess LH disrupts normal ovulation and can cause irregular periods, infertility, excess body hair, and acne. A very low ratio may suggest diminished ovarian reserve, poor egg quality, or approaching menopause. The ratio naturally changes throughout the menstrual cycle, being roughly 1:1 during the follicular phase but spiking during ovulation.
Factors like extreme stress, significant weight changes, and excessive exercise can alter this balance.
How this connects to other biomarkers
- LH/FSH Ratio > 2 in the early follicular phase (cycle day 2–5) is suggestive of PCOS (polycystic ovary syndrome), especially when combined with elevated Free Androgen Index (FAI), low Sex hormone-binding globulin (SHBG), and elevated HOMA-Index.
- In menopause, both Luteinizing hormone (Lutropin) and FSH, Follitropin rise but FSH rises more, lowering the ratio.
- In brain/pituitary failure (hypogonadotropic hypogonadism), both gonadotropins are low — the ratio looks preserved but the absolute values flag the diagnosis.
How often should I test LH/FSH ratio?
The LH/FSH ratio is reassessed alongside LH and FSH, typically day 2 to 5 of the cycle in premenopausal women, or yearly in postmenopausal women and men.
At baseline / for screening: Once every 12 months from age 35, with cycle phase noted in premenopausal women (typically drawn on day 2 to 5 of a 28-day cycle for baseline). More frequently during perimenopause.
When monitoring an intervention or change: Retest 6 to 12 weeks after starting or adjusting hormone therapy (HRT, oral contraceptives, fertility medication). Cycle phase matters as much as cadence, so match the cycle day across draws for meaningful comparison. In perimenopause, expect significant cycle-to-cycle variability that settles only after menopause is established.
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