Unit Converter
Follicle stimulating hormone (FSH)
Synonym
Follitropin
Units of measurement
mIU/mL, IU/L
FOLLICLE-STIMULATING HORMONE (FSH)
(Pituitary Gonadotropin – Key Marker for Ovarian Reserve, Menopause, Hypogonadism & Fertility)
Synonyms
- FSH
- Follicle-stimulating hormone
- Pituitary gonadotropin
- Gonadotropin (FSH component)
Units of Measurement
- mIU/mL
- IU/L
Unit Conversion
1 mIU/mL = 1 IU/L
(Values are numerically identical.)
Description
FSH is a glycoprotein hormone secreted by the anterior pituitary, regulated by:
- Gonadotropin-releasing hormone (GnRH)
- Feedback from estradiol, progesterone, inhibin, and testosterone
FSH is essential for:
- Ovarian follicle development in women
- Estrogen synthesis
- Spermatogenesis (Sertoli cell function) in men
FSH testing is one of the core hormones in fertility evaluation and gonadal function.
Physiological Role
In Women
- Stimulates growth of ovarian follicles
- Enhances estradiol production
- Critical for ovulation and menstrual cycle regulation
In Men
- Stimulates Sertoli cells in testes
- Supports spermatogenesis
- Essential for testicular volume and fertility
Clinical Significance
High FSH
Indicates decreased gonadal function (loss of negative feedback).
In Women
- Primary ovarian insufficiency (POI)
- Menopause
- Turner syndrome
- Gonadal dysgenesis
- Chemotherapy or radiation
- Autoimmune oophoritis
In Men
- Primary testicular failure
- Klinefelter syndrome
- Cryptorchidism
- Orchitis (mumps)
- Post-chemotherapy or radiation
Other Causes
- Gonadotropinoma (rare)
- Swyer syndrome
- Oophorectomy/testicular removal
Low FSH
Indicates central (pituitary or hypothalamic) dysfunction.
Causes:
- Hypopituitarism
- Hypothalamic amenorrhea (stress, weight loss, athletics)
- Hyperprolactinemia
- Kallmann syndrome
- Chronic systemic illness
- Anabolic steroid use
- Exogenous estrogens/testosterone
- Cushing’s syndrome
- Opioids, glucocorticoids
Reference Intervals
(Based on Tietz 8E + Endocrine Society + ASRM + Mayo)
Women (mIU/mL or IU/L)
Follicular phase
- 3 – 10
Mid-cycle peak (pre-ovulatory)
- 6 – 26
Luteal phase
- 1.5 – 9
Postmenopausal
- >25–134
(FSH usually >40 confirms menopause when combined with symptoms)
Men
- 1 – 12 mIU/mL
Children
- Values vary by Tanner stage
- Prepubertal: <3 mIU/mL
- Pubertal rise corresponds to testicular maturation
Units Description & Conversion Factors
mIU/mL ↔ IU/L
1 mIU/mL=1 IU/L1\ \text{mIU/mL} = 1\ \text{IU/L}1 mIU/mL=1 IU/L
Diagnostic Uses
1. Menopause & Ovarian Function
- High FSH (>40) + low estradiol → ovarian failure
- Used to diagnose menopause & POI
2. Infertility Evaluation (Women)
- Ovarian reserve testing
- Performed on Day 2–4 of menstrual cycle
- High FSH → diminished ovarian reserve
3. Infertility Evaluation (Men)
- High FSH suggests primary testicular failure
- Low sperm count + high FSH → non-obstructive azoospermia
4. Puberty Disorders
- Delayed puberty
- Precocious puberty
- Kallmann syndrome (low FSH)
5. Hypogonadism
Differentiate:
- Primary hypogonadism → high FSH
- Secondary hypogonadism → low/normal FSH
6. Monitoring Assisted Reproduction
FSH trends assist in controlled ovarian stimulation.
Analytical Notes
- Serum sample
- Should be collected in early follicular phase for cycle evaluation
- Pulsatile secretion → single value usually adequate
- Immunoassays commonly used
- Biotin interference possible
- Interpret with LH, estradiol, testosterone, AMH
Clinical Pearls
- FSH is high when gonads fail (loss of feedback).
- FSH is low when pituitary/hypothalamus fails.
- FSH >40 mIU/mL with low E2 strongly suggests menopause or POI.
- FSH is less stable than AMH for ovarian reserve testing but still clinically essential.
- In men, high FSH → impaired spermatogenesis; normal FSH with azoospermia → obstruction.
Interesting Fact
FSH and LH share the same alpha-subunit as TSH and hCG—only the beta-subunit gives hormone specificity.
SEO Unit Converter Text
FSH converter — convert between mIU/mL and IU/L. Includes phase-specific ranges for women, normal ranges for men, and diagnostic use in menopause, infertility, and hypogonadism.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition — Hormones.
- Endocrine Society Guidelines — Primary Ovarian Insufficiency & Hypogonadism.
- ASRM (American Society for Reproductive Medicine) — Fertility Evaluation.
- AACE/ACE Hormone Evaluation Guidelines.
- Mayo Clinic Laboratories — FSH.
- ARUP Consult — Gonadotropin Interpretation.
- MedlinePlus / NIH — FSH Test.