How to Determine if FSH and LH Levels Indicate Ovulation
FSH and LH levels can indicate ovulation when there is a characteristic LH surge in the mid-cycle, with LH levels rising 2-5 times above baseline, accompanied by a smaller rise in FSH levels. 1
Normal Hormonal Pattern During Ovulatory Cycle
- FSH and LH are released in a pulsatile manner from the pituitary gland in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus 1
- During the follicular phase (days 1-14 of a typical cycle), GnRH pulses occur every 1-1.5 hours 1
- During the luteal phase (days 15-28), GnRH pulses slow to every 2-4 hours 1
- A critical concentration of estradiol, produced by the dominant follicle, triggers positive feedback in the hypothalamus, resulting in the LH surge 1
- The LH surge initiates the process of ovulation 1
Specific Hormone Changes Indicating Ovulation
Pre-Ovulation (Early-Mid Follicular Phase)
- Normal FSH:LH ratio is approximately 1.34 or higher during early follicular phase (days 3-6) 2
- Baseline FSH and LH measurements should be taken between days 3-6 of the menstrual cycle 3
- For accurate assessment, calculate the average of three estimations taken 20 minutes apart 3
During Ovulation
- LH surge: A sharp increase in LH levels, typically 2-5 times above baseline 1
- FSH also rises during this time, but to a lesser degree than LH 1
- The LH surge typically occurs 24-36 hours before ovulation 1
Post-Ovulation (Luteal Phase)
- After ovulation, both FSH and LH levels decrease 1
- Progesterone levels rise significantly in the luteal phase 1
- Mid-luteal phase progesterone levels <6 nmol/L indicate anovulation 3
Laboratory Assessment for Ovulation
- Single measurements of FSH and LH are not reliable indicators of ovulation 2
- Serial measurements showing the characteristic surge pattern are more reliable 1
- Progesterone measurement during mid-luteal phase (approximately 7 days after suspected ovulation) is the most reliable hormonal indicator of ovulation 3
- Low mid-luteal phase progesterone levels (<6 nmol/L) indicate anovulation 3
Abnormal Patterns Suggesting Anovulation
- LH:FSH ratio >2 suggests polycystic ovary syndrome (PCOS) and likely anovulation 3
- FSH >35 IU/L and LH >11 IU/L suggest ovarian failure 3
- LH <7 IU/mL may indicate hypothalamic dysfunction 3
- Women with PCOS typically show hypersecretion of LH, ovarian theca stromal cell hyperactivity, and hypofunction of the FSH-granulosa cell axis 3
Age-Related Changes in FSH and LH
- Progressive increase in FSH levels begins as early as age 29-30 years 4
- LH levels show significant increase at age 35-36 years 4
- These changes occur even in women with regular ovulatory cycles and represent early markers of reproductive aging 4, 5
- The increase in FSH occurs approximately 5-6 years before menopause, while LH increases 3-4 years before menopause 5
Common Pitfalls in Interpretation
- Single measurements of FSH and LH are insufficient to confirm ovulation 2
- Timing of sample collection is critical - measurements should be taken at specific points in the cycle 3
- Some conditions like PCOS can show elevated LH levels throughout the cycle, masking the typical surge pattern 3
- Age-related changes in FSH and LH can affect interpretation of results 4, 5
- Medications, particularly hormonal contraceptives, can suppress normal FSH and LH patterns 3