Follicle-Stimulating Hormone (FSH) in Women: Function and Normal Values
Follicle-stimulating hormone (FSH) is one of the main hormones that regulate the ovarian cycle. Along with LH, it controls the maturation of follicles in the ovaries and, therefore, ovulation.
Knowing the normal levels of FSH in women is important. It helps diagnose issues related to ovarian reserve. It is also useful for planning assisted reproductive treatments and evaluating fertility.
What is FSH and How Does It Work?
FSH is secreted by the pituitary gland.
- It stimulates the growth and maturation of ovarian follicles.
- It works together with LH to trigger ovulation.
- Its levels fluctuate throughout the menstrual cycle:
- Early follicular phase: moderate levels
- Pre-ovulation: a slight FSH peak along with LH
- Luteal phase: low levels
Role of FSH in the Menstrual Cycle
- Beginning of the follicular phase:
FSH promotes the selection of several follicles, one of which becomes dominant. - Maturation of the dominant follicle:
It increases estrogen production, which in turn provides feedback to the pituitary and regulates further FSH secretion. - LH surge and ovulation:
Although LH is mainly responsible for the follicular rupture, FSH contributes to the process. - Regulation of the luteal phase:
FSH levels drop, allowing the formation of the corpus luteum and the production of progesterone.
Comparative Diagram of FSH, LH, and Estrogens in the Menstrual Cycle
Normal FSH Levels in Women
These ranges may vary slightly depending on the laboratory.
How to Interpret FSH Levels for Conception
High FSH before age 35:
- May indicate a reduced ovarian reserve.
- Requires assessment of AMH and antral follicle count.
Low FSH:
- May be associated with hypopituitarism or central ovarian failure.
Normal levels:
- Indicate a good natural prognosis.
- If conception is difficult, other causes of infertility should be investigated (PCOS, male factor, etc.).
FSH and Maternal Age Relationship
- With age, baseline FSH levels tend to increase.
- After age 35, moderately high FSH is common and may indicate declining fertility.
- In women over 40, the postmenopausal FSH peak is significantly higher, confirming the end of the reproductive stage.
Frequently Asked Questions (FAQ)
What are the normal FSH levels in women?
They depend on the phase of the cycle:
- Early follicular phase: 3.5 to 12.5 mIU/mL
- Ovulatory peak: 4.7 to 21.5 mIU/mL
- Luteal phase: 1.7 to 7.7 mIU/mL
What does a high FSH level before age 35 indicate?
It may suggest low ovarian reserve or early perimenopause. It is advisable to complete testing with AMH and antral follicle count ultrasound.
How does maternal age affect FSH levels?
As age increases, baseline FSH levels tend to rise, reflecting a decrease in ovarian reserve.
Follicle-Stimulating Hormone (FSH) is key to understanding ovarian function and planning fertility treatments.
At Fertility Madrid, we offer a complete analysis of your hormone levels and follow-up ultrasounds to design the best reproductive protocol.
Book your first free consultation and optimize your ovarian reserve.
If you have difficulty distinguishing between implantation bleeding and a normal period, or if you’re planning a pregnancy and have questions about your reproductive health, it’s advisable to speak with a doctor.
