You feel terrible. You go to your doctor and say, “I think I’m in menopause. Can you test my hormones?” The doctor draws your blood, measures your FSH (Follicle Stimulating Hormone), and calls you back a week later. “Your FSH is 15. You aren’t in menopause yet.” Or, “Your FSH is 40. You are definitely in menopause.”
Both of these statements might be wrong. Relying on a single FSH blood test to diagnose where you are in the transition is one of the most common medical errors in midlife care. It is a snapshot of a moving target.
What is FSH?
FSH is the messenger. It is the hormone your brain (pituitary gland) sends to your ovaries to say: “Please grow an egg.”
- In your 20s: The ovaries hear the whisper. The brain only needs to send a little bit of FSH (Level < 10) to get a response.
- In Perimenopause: The ovaries are going deaf. They ignore the signal. The brain starts screaming. It pumps out massive amounts of FSH to try to wake the ovaries up. FSH levels rise to 30, 50, or even 100.
The Fluctuation Problem
Here is the trap: FSH fluctuates wildly during perimenopause. In post-menopause (when the ovaries are dead), FSH stays permanently high (usually > 30). But in peri-menopause, it acts like a yo-yo.
- Monday: Your ovaries are asleep. Your brain screams. FSH is 60. (Lab says: “Menopausal”).
- Thursday: Your ovaries suddenly wake up and produce an egg. They produce estrogen. The brain sees the estrogen and stops screaming. FSH drops to 8. (Lab says: “Fertile/Normal”).
If you catch your blood on Monday, you get one diagnosis. If you catch it on Thursday, you get another. Neither is “the truth.” They are just moments in time.
Treating the Number, Not the Patient
The danger of the FSH Trap is that it delays treatment. A woman comes in with hot flashes, rage, and insomnia. Her FSH comes back “Normal” (because she had a good ovarian day). The doctor says: “Your labs are normal. You aren’t in perimenopause. It must be depression. Here is an antidepressant.” She is denied HRT because the number didn’t match the textbook definition, even though her symptoms are screaming perimenopause.
When IS the Test Useful?
FSH testing is rarely useful for diagnosing perimenopause (symptoms are a better guide). However, it is useful for:
- Women with a Hysterectomy: If you don’t have a uterus, you don’t have a period to track. You can’t use the “12-Month Clock.” In this case, doctors monitor FSH over time. If it stays consistently high (>30) across multiple tests, it confirms ovarian retirement.
- Premature Ovarian Insufficiency (POI): If you are 32 and stopped bleeding, a high FSH is a critical diagnostic marker for premature menopause.
The Better Metric
Forget the blood test. Trust the Bleeding Pattern.
- Regular Cycles: Early Reproductive.
- 7-Day Variance: Early Transition.
- Skipped Cycles (60+ days): Late Transition.
- No Period for 12 Months: Menopause.
Your calendar tells the truth. Your blood just tells you the weather on the day of the draw. Do not let a “normal” lab result gaslight you out of getting help for your symptoms.