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Reading FSH in context
- FSH below 10 IU/L — In a woman with a functioning menstrual cycle, this is generally in the premenopausal range. In perimenopause, FSH can dip back to this range between cycles even when other signs of transition are present. A value below 10 does not rule out early perimenopause.
- FSH 10–25 IU/L — The most ambiguous zone. This range overlaps with normal premenopausal variation in the early follicular phase, with early perimenopause, and with the fluctuations of mid-transition. Without cycle context (day of cycle, recent bleeding pattern, symptoms), this number provides minimal information.
- FSH above 25 IU/L — Associated with late perimenopause and menopause, but in perimenopause the same woman can reach this range one cycle and fall below it the next. STRAW+10 does not use a single FSH above 25 to define any transition stage. For diagnosing postmenopause after natural final menstrual period, guidelines generally use FSH >30–40 IU/L on two separate draws, in the context of 12 months without a period.
- The one place FSH matters reliably: POI. For women under 40 with amenorrhoea or marked cycle disruption, two FSH readings above 25 IU/L, at least four weeks apart, in the context of absent or irregular periods for four or more months, are a key diagnostic criterion for premature ovarian insufficiency (POI). This is a specific, serial-measurement protocol — not a one-off test.
Reading AMH in context
What AMH does well
- AMH declines across the reproductive years and accelerates its decline as the menopause transition approaches.
- AMH often falls below detectable limits several years before the final menstrual period.
- Very low AMH (around or below 0.1 ng/mL) is associated, on average, with the final period occurring within roughly three years, though with considerable individual variability.
This makes AMH useful for:
- Fertility counselling and understanding remaining reproductive window.
- Surgical or treatment planning (e.g., chemotherapy, radiation, or surgery that may affect ovarian function).
- Supplementary assessment in a POI workup alongside FSH.
What AMH does not do well
- AMH cannot tell you whether you are currently in perimenopause.
- Low AMH does not mean you are symptomatic, and a “normal” AMH does not exclude hormonally driven symptoms.
- Correlation between AMH level and vasomotor symptom burden is weak.
- AMH does not reliably predict the type or severity of perimenopausal symptoms; it reflects follicle count, not estrogen activity or cycle irregularity.
The 4-step framework for using FSH and AMH results
- Start with your cycle pattern.
- Are cycles lengthening, shortening, or becoming highly variable?
- Have you had any gaps of 60 days or more?
- This is the primary data; STRAW+10 is built on bleeding pattern, not labs.
- Layer in your symptoms.
- Hot flashes, night sweats, sleep disruption, mood changes, vaginal dryness, brain fog.
- Note duration, severity, and progression.
- Apply the number.
- Use FSH or AMH as an additional data point against an already clear clinical picture.
- Example: If cycles are clearly in late-transition territory (60+ day gaps) with significant vasomotor symptoms, a single FSH of 22 IU/L does not change the staging.
- Escalate if the picture is misaligned.
- If the lab result does not fit the cycle pattern and symptoms, that mismatch is a reason for serial measurements, specialist review, or workup for other diagnoses — not a reason to rely on the single number.
Inhibin B — an early but rarely used marker
Inhibin B is a protein produced by developing follicles that suppresses FSH release. It declines earlier than FSH rises, making it a potentially sensitive early marker of diminishing ovarian reserve. In research settings, falling inhibin B has been used as an early signal of the beginning of the menopause transition.
In routine clinical practice, inhibin B is rarely ordered because it is less widely available, reference ranges are less established than for FSH and AMH, and it usually does not change management for most patients. It is a legitimate marker, but it has not been incorporated into standard clinical algorithms.