What is lh and fsh

Last updated: April 1, 2026

Quick Answer: LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone) are reproductive hormones produced by the pituitary gland that regulate fertility, menstrual cycles, and sex hormone production in both men and women.

Key Facts

Overview

LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone) are two essential reproductive hormones produced by the anterior pituitary gland. Together, they form the hypothalamic-pituitary-gonadal axis, a complex system that regulates fertility and sexual function in both men and women.

Follicle-Stimulating Hormone (FSH)

FSH initiates the reproductive cycle in women by stimulating the growth of follicles in the ovaries, which contain eggs. These developing follicles produce estrogen, which thickens the uterine lining. In men, FSH stimulates the seminiferous tubules in the testes to produce sperm. FSH levels gradually increase during the menstrual cycle and peak just before ovulation. FSH is continuously produced in men to maintain ongoing sperm production.

Luteinizing Hormone (LH)

LH works in coordination with FSH to complete the reproductive cycle. In women, a significant surge in LH triggers ovulation around day 14 of the menstrual cycle, causing the mature follicle to release an egg. After ovulation, LH stimulates the corpus luteum to produce progesterone, essential for maintaining the uterine lining. In men, LH stimulates Leydig cells to produce testosterone, which supports sperm development and sexual function.

Hormonal Coordination

LH and FSH work together in a tightly coordinated cycle controlled by GnRH (Gonadotropin-Releasing Hormone) from the hypothalamus. The rising estrogen levels from FSH-stimulated follicles initially suppress LH and FSH (negative feedback), then trigger the LH surge that causes ovulation (positive feedback). This sophisticated coordination ensures proper timing of ovulation and hormone production.

Clinical Significance

Blood tests measuring both LH and FSH levels help diagnose fertility problems, hormonal imbalances, and menopause. The LH:FSH ratio provides additional diagnostic information. Abnormal ratios may indicate conditions like PCOS, ovarian failure, or pituitary disorders. Healthcare providers often order both tests together for comprehensive hormonal evaluation.

Related Questions

What is the difference between LH and FSH?

FSH stimulates follicle/sperm development, while LH triggers ovulation and hormone production. FSH acts first in the cycle to prepare the egg or sperm, then LH surges to trigger ovulation or support testosterone production. Both are essential but have different specific functions.

What is the LH to FSH ratio?

The LH to FSH ratio compares the levels of these two hormones and can help diagnose reproductive conditions. In women with PCOS, the ratio is typically elevated (3:1 or higher) compared to the normal ratio of approximately 1:1 to 2:1.

What does the LH:FSH ratio indicate?

The LH:FSH ratio helps diagnose reproductive conditions. In normal women, the ratio is typically 1:1 during the follicular phase. In PCOS, the ratio is often elevated at 2:1 or higher, indicating excessive LH relative to FSH production.

What happens during the LH surge?

The LH surge is a dramatic increase in LH levels that occurs mid-cycle and triggers ovulation in women. This surge causes the mature egg to be released from the ovary and typically occurs about 24-36 hours before ovulation.

When are LH and FSH tests ordered?

LH and FSH tests are ordered when evaluating infertility, irregular periods, amenorrhea (missed periods), menopausal symptoms, and hormonal imbalances. The tests help determine if reproductive problems stem from the ovaries, pituitary gland, or hypothalamus.

How do LH and FSH change during menopause?

During menopause, both LH and FSH levels increase significantly as the pituitary gland attempts to stimulate ovaries that are no longer responsive. Elevated levels (FSH typically above 30 IU/L) indicate declining estrogen production.

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Sources

  1. MedlinePlus - FSH (Follicle Stimulating Hormone) Test Public Domain
  2. Wikipedia - Gonadotropin CC-BY-SA-3.0
  3. Mayo Clinic - Polycystic Ovary Syndrome CC-BY-NC-ND-4.0