Luteinizing Hormone (LH) is a chemical messenger in the body, important for the female menstrual cycle and reproductive health. Produced by the pituitary gland in the brain, LH helps regulate processes within the ovaries. Fluctuating levels indicate reproductive activity. Understanding LH patterns helps identify key menstrual cycle phases.
The Ovulatory LH Surge
The menstrual cycle begins with the follicular phase, during which follicle-stimulating hormone (FSH) prompts the ovaries to develop small sacs called follicles, each containing an egg. As these follicles mature, they produce increasing amounts of estrogen. This rising estrogen level signals the pituitary gland.
Once estrogen reaches a certain concentration, it triggers an increase in luteinizing hormone, known as the “LH surge.” This surge occurs 24 to 36 hours before ovulation. The LH surge acts as a signal, causing the most mature follicle in the ovary to rupture and release its egg. This egg release is ovulation.
What Happens to LH After Ovulation
Immediately following the LH surge and egg release, luteinizing hormone levels drop sharply. This decline occurs because the hormonal feedback loop that initiated the surge changes. The ruptured follicle transforms into a temporary structure called the corpus luteum, which begins to produce progesterone.
Progesterone, along with some estrogen, prepares the uterine lining for a potential pregnancy. The presence of these hormones signals the pituitary gland, suppressing LH release. LH returns to lower, baseline levels characteristic of the luteal phase. If pregnancy does not occur, the corpus luteum eventually breaks down, leading to a decrease in progesterone and the start of menstruation. LH levels rise again for the next cycle.
Reasons for Elevated LH After Ovulation
While LH levels decrease after ovulation, there are situations where they might appear elevated or remain high. One common reason for persistently elevated LH levels is Polycystic Ovary Syndrome (PCOS). In PCOS, hormonal imbalances lead to chronically high LH levels, often in an elevated ratio compared to FSH. This interferes with regular ovulation, causing irregular periods.
Another scenario involves perimenopause and menopause. As women approach menopause, ovarian function declines. In an attempt to stimulate the ovaries to produce more estrogen, the pituitary gland increases its production of LH. LH levels become consistently elevated during perimenopause and remain high after menopause.
An ovulation predictor kit (OPK) might show a positive result after ovulation due to human chorionic gonadotropin (hCG), the hormone detected by pregnancy tests. hCG has a molecular structure similar to LH, allowing it to bind to the same receptors and trigger a positive result on an OPK, even without an actual LH surge. This can happen if a person is in the very early stages of pregnancy.
Misinterpreting OPK results can also lead to a perception of elevated LH. Ovulation tests require the test line to be as dark as or darker than the control line for a positive result, indicating a surge. Faint lines can appear at various times during the cycle as some LH is always present, but these do not signify a surge. Some individuals may also experience multiple or prolonged LH surges that do not always lead to ovulation, or they may simply have naturally higher baseline LH levels, which can lead to confusion when interpreting test results.