Luteinizing Hormone (LH) is a hormone produced by the pituitary gland, a small organ located at the base of the brain. In women, LH plays a role in regulating the menstrual cycle and fertility. It works alongside other hormones to coordinate the sequence of events that lead to ovulation. Understanding LH patterns throughout the cycle is helpful for individuals monitoring their fertility, particularly when attempting to conceive. LH levels fluctuate throughout the month, providing important signals about reproductive health.
Understanding the LH Surge
The LH surge is a rapid and substantial increase in luteinizing hormone. This surge is a central event in the menstrual cycle, signaling that the body is preparing for ovulation. It is triggered by rising levels of estrogen, produced by a maturing ovarian follicle.
As estrogen levels reach a threshold, they switch from negative to positive feedback on the pituitary gland and hypothalamus. This causes the pituitary gland to release a large amount of LH. The elevated LH then signals the dominant follicle, prompting its maturation and preparation for releasing an egg.
When Ovulation Occurs
Ovulation, the process where a mature egg is released from the ovary, occurs after the LH surge. This critical event typically happens between 24 and 36 hours after the beginning of the LH surge, or around 10-12 hours after the LH peak. The LH surge directly triggers the follicle to rupture and release the egg into the fallopian tube.
While precise timing varies, the LH surge reliably indicates imminent ovulation. The released egg remains viable for fertilization for approximately 12 to 24 hours. This narrow window highlights the sequence of events following the LH surge for fertility awareness.
LH Levels Immediately After the Surge
After the LH surge triggers ovulation, LH levels decline rapidly. The peak of the LH surge precedes the actual egg release. By the time ovulation occurs, LH levels are already decreasing from their highest point.
Therefore, LH does not remain high on the day of ovulation itself. The surge reaches its maximum, initiates the ovulatory process, and then recedes. Typically, LH levels return to their baseline shortly after ovulation, often within 24 to 48 hours. This decline confirms the LH surge has fulfilled its role in triggering egg release.
Using LH to Track Your Cycle
Ovulation predictor kits (OPKs) are a common tool that detect the LH surge in urine, providing a practical way to track fertility at home. These kits identify increased LH levels, which signals that ovulation is likely within 24 to 36 hours. Testing typically involves holding a test stick in a urine stream or dipping it into a collected urine sample.
For accurate results, avoid excessive fluid intake for a few hours before testing to ensure a concentrated urine sample. A positive OPK result, often indicated by a test line as dark or darker than a control line, suggests the fertile window has opened. While OPKs are highly accurate in detecting the LH surge (approximately 90-99% accurate when used correctly), they do not confirm ovulation has definitively occurred. They serve as a reliable predictor, guiding individuals on the best time for intercourse to increase conception chances.