What it measures
- FSH (follicle stimulating hormone)
What does FSH do?
Follicle stimulating hormone is made by the pituitary gland. In women it stimulates the ovaries to grow follicles, each containing an egg. In men it supports sperm production.
What your FSH result can show
- A raised FSH early in the cycle can mean the ovaries need more encouragement to respond, which can happen as ovarian reserve falls and around the menopause.
- Low FSH can point to a problem with the pituitary gland, or can be caused by stress, low body weight or very intense exercise.
FSH changes from cycle to cycle, so a single result is a snapshot. For ovarian reserve, many people pair it with an AMH test, which is more stable.
Who it’s for
- Trying to conceive
- Irregular or missed periods
- Perimenopause symptoms under the age of 45
- Men investigating fertility
How to prepare
- Drink plenty of water beforehand; it makes the sample quicker and easier to take.
- You don’t need to fast.
- If you have periods, book for day 2–5 of your cycle (day 1 is the first day of bleeding).
- Stop biotin (vitamin B7) supplements 48 hours before, as biotin can affect hormone and thyroid results.
FSH (Follicle Stimulating Hormone) Blood Test: your questions
When should I have an FSH test?
On day 2–5 of your cycle, where day 1 is the first day of your period. If your periods are irregular or absent, you can test on any day.
Can FSH confirm the menopause?
Over 45, the menopause is usually diagnosed from your symptoms and periods alone. FSH can help if you’re under 45 or your symptoms are unclear.
Information on this page is general and doesn’t replace advice from your GP, midwife or consultant. If you feel unwell or are worried about symptoms, contact your GP, call NHS 111 or, in an emergency, 999.