What this marker measures
FSH on day 2–3 of the menstrual cycle (early follicular phase) is used to assess ovarian reserve in fertility evaluation. A high day-3 FSH is associated with poorer response to fertility treatments.
High or low: what it can mean
High FSH
Very high FSH in females, particularly at the beginning of the menstrual cycle, often signals diminished ovarian reserve or menopause. In males, high FSH usually indicates impaired sperm production.
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Low FSH
Low FSH can prevent ovulation and impair fertility. Causes are similar to low LH — hypothalamic or pituitary dysfunction, eating disorders, or extreme exercise.
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Frequently asked questions
What is FSH?
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FSH is produced by the pituitary gland and stimulates follicle development in the ovaries and sperm production in the testes. It is a key indicator of ovarian and testicular reserve.
What does FSH measure?
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FSH on day 2–3 of the menstrual cycle (early follicular phase) is used to assess ovarian reserve in fertility evaluation. A high day-3 FSH is associated with poorer response to fertility treatments.
What does high FSH mean?
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Very high FSH in females, particularly at the beginning of the menstrual cycle, often signals diminished ovarian reserve or menopause. In males, high FSH usually indicates impaired sperm production.
What does low FSH mean?
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Low FSH can prevent ovulation and impair fertility. Causes are similar to low LH — hypothalamic or pituitary dysfunction, eating disorders, or extreme exercise.
Related biomarkers
Editorial note
LabTestly explains lab markers using plain-English educational content. Reference ranges may vary by laboratory and should be interpreted with a clinician.
Educational content · Editorially reviewed for clarity · Last updated
Common sources used for lab-test education
Not medical advice
This page is for general understanding only and does not replace medical advice from your clinician. Reference ranges can vary by laboratory, age, sex, pregnancy status, medications, and clinical context.