Luteinizing Hormone (LH) is a glycoprotein hormone produced by the pituitary gland. This hormone plays a role in the reproductive cycle, stimulating changes in the ovaries that regulate the menstrual cycle. Throughout the cycle, LH levels fluctuate widely, controlling the timing of egg maturation and release. Tracking the patterns of this hormone’s rise and fall is a primary method for understanding a woman’s fertility status.
The Purpose of the LH Surge
The entire sequence of events leading to egg release is initiated by a dramatic spike in LH concentration known as the LH surge. This surge is triggered by a preceding rise in estrogen, which occurs when a dominant ovarian follicle has matured. The mature follicle signals the pituitary gland through the increase in estrogen, causing a rapid release of LH.
The LH surge signals that ovulation is imminent. The surge lasts approximately 24 to 48 hours, providing the hormonal stimulus necessary to rupture the mature follicle. This influx of hormone acts on the ovarian tissue, facilitating the breakdown of the follicle wall. The egg release follows the peak of the hormone concentration.
The Timing of Ovulation
Ovulation, the moment the egg is released from the ovary, occurs after the LH surge has begun. The egg is typically released between 24 and 36 hours following the initial rise in LH levels. This time lag allows the hormone to fully stimulate the final steps of follicular maturation and rupture.
Ovulation often occurs approximately 12 to 20 hours after the hormone reaches its highest concentration, or its peak. Therefore, on the actual day of ovulation, LH levels are generally at their peak or still very high. The hormone level does not begin to drop until after the egg has successfully left the ovary. This timing defines the most fertile window, which includes the day of the peak and the day of ovulation.
The Post-Ovulation LH Decline
The answer to whether LH levels drop on ovulation day is generally no, but the decline begins immediately afterward. Once the mature egg is released, the remnants of the ovarian follicle transform into a temporary structure called the corpus luteum.
The corpus luteum begins to secrete large amounts of progesterone. Progesterone then acts on the pituitary gland and the hypothalamus in a process called negative feedback. This feedback loop actively suppresses the further release of LH, causing the hormone’s concentration to rapidly fall back to its low baseline level.
The drop in LH confirms that ovulation has successfully occurred and the body is moving into the luteal phase of the cycle. LH levels typically return to baseline within 24 to 48 hours after the egg release is complete. This rapid decline prepares the body for either menstruation or the hormonal demands of a potential pregnancy.