Luteinizing hormone (LH) is a reproductive hormone released by the pituitary gland, which is located in the brain. This hormone plays a significant role in regulating the menstrual cycle and is especially important for fertility. LH levels fluctuate throughout the cycle, but the dramatic rise and subsequent fall orchestrates the release of a mature egg from the ovary. Understanding this timing is necessary to know how long LH remains elevated after ovulation.
The Trigger for Ovulation
The process of releasing an egg is preceded by a rapid and massive spike in LH, known as the LH surge. This surge is the definitive signal sent from the pituitary gland to the ovary, instructing the most mature follicle to rupture and release its egg. It is triggered when the hormone estrogen, produced by the developing follicle, reaches a high threshold in the bloodstream. The surge in LH levels typically lasts between 24 and 48 hours. Ovulation itself occurs within 12 to 36 hours after the LH peak.
The Immediate Drop After Ovulation
Once the LH surge successfully triggers the release of the egg, the pituitary gland immediately reduces its production of LH. This quick slowdown occurs because the hormone’s primary task—initiating ovulation—is complete. LH levels fall very rapidly back toward their baseline, or pre-surge, levels. The decline often begins within 24 to 48 hours after the peak of the surge. This prompt reduction is a result of the body’s hormonal negative feedback system, which works to restore balance after the massive mid-cycle spike. For most individuals, the LH level will have returned to a non-surge baseline within two days following the peak.
LH Levels During the Luteal Phase
Following the immediate post-ovulation drop, LH does not vanish entirely from the bloodstream. It remains present at a low, steady basal level throughout the second half of the cycle, known as the luteal phase. The sustained, low presence of LH is necessary to support the corpus luteum, which is the structure formed from the remnants of the ruptured follicle. The corpus luteum is responsible for producing the hormone progesterone, which prepares the uterine lining for a potential pregnancy. If conception does not occur, the corpus luteum eventually degrades, and LH levels remain low until the next cycle begins. The typical LH range during the luteal phase is between 0.61 and 16.3 IU/mL, compared to surge levels of 21.9 to 56.6 IU/mL or higher.
Practical Application: Reading Ovulation Tests
The rapid decline of LH after ovulation has direct implications for using at-home Ovulation Predictor Kits (OPKs). These tests are designed to detect the LH surge in urine, which signals that ovulation is imminent, usually within 24 to 36 hours. A positive test, where the line is as dark as or darker than the control line, indicates the surge is happening. Once a positive result is achieved, continued daily testing is generally unnecessary because the hormone level is expected to fall quickly. A subsequent negative test confirms that the surge has passed and that ovulation has likely occurred. It is common to see a faint test line on an OPK throughout the luteal phase. This faint line is caused by the low, basal level of LH circulating to support the corpus luteum. This faint line should not be mistaken for a renewed surge or a sign that ovulation is about to happen again.