What do LH (Luteinizing Hormone), estradiol, progesterone, and FSH (Follicle-Stimulating Hormone) mean in the context of the reproductive system?

Understanding Reproductive Hormones: LH, FSH, Estradiol, and Progesterone

Luteinizing Hormone (LH), Follicle-Stimulating Hormone (FSH), estradiol, and progesterone are critical reproductive hormones that regulate ovulation, menstruation, and fertility in women, with distinct roles in the menstrual cycle and reproductive health.

Definition and Function of Each Hormone

Luteinizing Hormone (LH)

• A gonadotropin hormone produced by the anterior pituitary gland
• Primary functions:
  • Triggers ovulation in women when it surges at mid-cycle 1
  • Stimulates the ovarian theca cells to produce androgens 1
  • Supports corpus luteum development after ovulation 2
  • Baseline levels should be assessed at age 13 years in at-risk populations 1

Follicle-Stimulating Hormone (FSH)

• A gonadotropin hormone also produced by the anterior pituitary gland
• Primary functions:
  • Stimulates follicular development in the ovaries 1
  • Promotes estradiol production by granulosa cells 1
  • Higher than LH during early follicular phase 2
  • Increases significantly with advancing age, particularly after age 39 3
  • Elevated levels (>35 IU/L) may indicate ovarian failure 1

Estradiol

• The primary estrogen hormone produced mainly by ovarian follicles
• Primary functions:
  • Promotes development of female secondary sexual characteristics
  • Stimulates endometrial growth during the follicular phase 1
  • Triggers LH surge at mid-cycle through positive feedback on hypothalamus 1
  • Maintains bone density and cardiovascular health 1
  • Levels peak just before ovulation 4

Progesterone

• A steroid hormone produced primarily by the corpus luteum after ovulation
• Primary functions:
  • Prepares the endometrium for potential implantation 2
  • Maintains pregnancy if fertilization occurs
  • Inhibits further follicular development during luteal phase
  • Levels are 10-15 times higher in luteal phase (12.4 ± 2.3 ng/ml) compared to follicular phase (0.65 ± 0.12 ng/ml) 2
  • Peak occurs at mid-luteal phase 2

Hormonal Patterns During Normal Menstrual Cycle

Follicular Phase (Days 1-14)

• FSH levels rise early, stimulating follicular development 4
• FSH is typically higher than LH during this phase 2
• Estradiol gradually increases as follicles develop
• Progesterone remains low (approximately 0.65 ± 0.12 ng/ml) 2

Ovulatory Phase (Mid-cycle)

• Sharp LH surge triggers ovulation 2
• FSH also peaks but to a lesser extent 2, 4
• Estradiol reaches its highest level just before the LH surge 4
• Progesterone begins to rise slightly

Luteal Phase (Days 15-28)

• LH and FSH levels decline
• Progesterone rises significantly (approximately 12.4 ± 2.3 ng/ml) 2
• Estradiol rises to a second, smaller peak
• Progesterone peak occurs at mid-luteal phase 2
• Luteal phase typically lasts 12-15 days 2

Clinical Significance and Assessment

Normal Ovulatory Cycle Criteria

• Mid-cycle LH peak 2
• Progesterone levels 10-15 times higher in luteal phase than follicular phase 2
• Progesterone peak at mid-luteal phase 2
• Luteal phase duration of 12-15 days 2

Hormonal Changes with Age

• FSH levels increase significantly after age 39 3
• LH levels remain relatively stable until the last 5 years before menopause 3
• Estradiol patterns show minor fluctuations but generally remain in normal range 3
• Luteal progesterone levels decline in women over 30 5

Abnormal Patterns

• Elevated FSH (>35 IU/L) with normal or elevated LH (>11 IU/L) suggests primary ovarian failure 1
• LH/FSH ratio >2 may indicate polycystic ovary syndrome (PCOS) 1
• Low LH (<7 IU/ml) may suggest hypothalamic dysfunction 1
• Low progesterone (<6 nmol/L) in luteal phase indicates anovulation 1

Clinical Applications

Diagnostic Uses

• Evaluation of infertility
• Assessment of ovarian function and reserve
• Diagnosis of PCOS, primary ovarian failure, or hypothalamic amenorrhea
• Monitoring response to fertility treatments 6, 7
• Evaluation of early or delayed puberty 1

Therapeutic Interventions

• Clomiphene citrate works by competing with estrogen for receptor sites, increasing gonadotropin release (FSH and LH), which stimulates follicular development 6
• Letrozole inhibits estrogen biosynthesis, leading to increased FSH release without affecting adrenal, thyroid, or aldosterone synthesis 7
• Hormone replacement therapy may be needed in cases of hypogonadism 1

Important Clinical Considerations

• Timing of blood sampling is crucial for accurate interpretation
• Hormone levels should be interpreted in context of menstrual cycle phase
• Single measurements may be misleading; serial measurements provide better information
• Abnormal hormone patterns require further investigation and possible referral to specialists

By understanding these reproductive hormones and their interactions, clinicians can better diagnose and manage various reproductive disorders, optimize fertility treatments, and address hormonal imbalances affecting women's health.