Luteinizing Hormone (LH) is a gonadotropin released by the pituitary gland. Its primary function within the menstrual cycle is to signal the final maturation and release of an egg from the ovary. Ovulation is the process where a mature egg is ejected from the ovary after developing within a follicle. The rapid increase in LH concentration, known as the LH surge, instructs the start of ovulation roughly 24 to 36 hours later. This hormonal cascade is tightly regulated, but the signal does not always result in the intended action. Sometimes, the hormonal signal to ovulate occurs, but the physical release of the egg does not follow.
The Difference Between an LH Surge and Ovulation
Yes, an LH surge can occur without ovulation; this phenomenon is known as an anovulatory cycle. An ovulation predictor kit (OPK) detects the spike in LH, confirming the brain has sent the signal to the ovary. However, the surge does not guarantee the successful rupture of the ovarian follicle.
This physiological failure occurs when the developing follicle is not mature enough or is unable to respond to the LH signal, even when the hormone is present at high levels. The pituitary gland releases the LH correctly, but the ovary fails to complete the process. In a normal cycle, the LH surge triggers enzymes that break down the follicular wall, allowing the egg to escape. In an anovulatory cycle, this final step is blocked or incomplete.
Conditions That Cause Anovulatory Cycles
The most common underlying cause of chronic anovulation is Polycystic Ovary Syndrome (PCOS). This complex endocrine disorder involves a hormonal imbalance that prevents follicles from maturing fully. In PCOS, elevated levels of androgens (male hormones) interfere with development, causing follicles to stall and fail to ovulate despite a strong LH signal. This often results in multiple small, underdeveloped follicles remaining on the ovary.
Fluctuations in body weight, including being severely underweight (low BMI) or having obesity (high BMI), can disrupt the hypothalamic-pituitary-ovarian (HPO) axis. Adipose tissue influences estrogen production, and too much or too little body fat alters the hormonal feedback loops required for ovulation. Excessive, high-intensity exercise, particularly endurance training, can also create an energy deficiency that suppresses the hormonal pulses needed for proper follicular development.
Thyroid dysfunction, especially hypothyroidism, is another frequent cause, as thyroid hormones are connected with reproductive hormone metabolism. Low thyroid function can increase prolactin levels, which suppresses the release of gonadotropins like LH. High levels of chronic stress also impact the HPO axis through the stress hormone cortisol, which can inhibit the signals needed to trigger successful ovulation.
How to Identify an Anovulatory Cycle
A positive LH test indicates a surge, but tracking other biomarkers is necessary to confirm that ovulation actually occurred. The most accessible at-home method is tracking Basal Body Temperature (BBT), the body’s lowest resting temperature. Following ovulation, progesterone release causes a sustained temperature shift of about 0.5 to 1.0 degrees Fahrenheit. This shift is typically absent or inconsistent in an anovulatory cycle.
Cervical Mucus and Bleeding Patterns
Another indicator is the lack of a characteristic change in cervical mucus, which should become thin, clear, and stretchy, resembling egg whites, just before and during ovulation. Without successful ovulation, this fertile-quality mucus may not appear or may be present multiple times as the body attempts to ovulate repeatedly. Anovulation can also lead to irregular bleeding patterns, sometimes called anovulatory bleeding, which may be lighter, heavier, or more erratic than a typical menstrual period.
Progesterone Testing
For a more direct confirmation, at-home tests measure the progesterone metabolite PdG in urine after the expected ovulation date. These tests provide evidence of progesterone production, which only happens after the egg is released.
When to Seek Medical Guidance
Experiencing an occasional anovulatory cycle is common and usually not a cause for concern, especially during acute illness, high stress, or following changes in diet or exercise. However, a pattern of anovulation warrants professional consultation to investigate the underlying cause. You should seek medical guidance if you suspect or confirm anovulation in two or more consecutive cycles.
A healthcare provider can order blood tests, such as a mid-luteal phase progesterone test, for definitive confirmation of ovulation. They may also check levels of other hormones, including Thyroid-Stimulating Hormone (TSH) and prolactin, to rule out systemic endocrine conditions. Treatment is condition-specific but often begins with lifestyle modifications, such as targeted weight management or stress reduction. If pregnancy is desired, medication can be prescribed to induce ovulation, stimulating the ovary to mature and release an egg.