The LH surge is the sharp rise in luteinizing hormone (LH) that triggers ovulation within 24–36 hours. The LH peak is the highest point of that surge, typically occurring 24 hours before egg release. Learn what triggers the LH surge before ovulation, how estrogen and GnRH drive the process, and why timing matters for fertility. This surge in LH is what triggers the release of an egg from the dominant follicle typically 24-36 hours later, enabling ovulation. An LH surge does not always guarantee that a successful ovulation will occur, but tracking this hormone can still give you vital information about your fertile window. Around the midpoint of your cycle, levels of luteinizing hormone (LH) surge. This marks the start of your fertility window. An LH surge is a rapid rise in luteinizing hormone that triggers your ovary to release an egg. It’s the hormonal event that kicks off ovulation, and detecting it is one of the most reliable ways to pinpoint your fertile window. When the body’s levels of luteinizing hormone (LH) rise, it triggers the start of ovulation, the most fertile period of the menstrual cycle. Tracking the surge in luteinizing hormone levels can. This acute elevation is known as the LH surge, and it is the direct biological signal for the ovary to release a mature egg, a process called ovulation. Ovulation typically follows this hormonal signal within 24 to 36 hours, defining the most fertile window of the cycle. Like estrogen and progesterone, LH is another important hormone that surges during your cycle to trigger processes like ovulation. To better understand what an LH surge is, it can help to break down your cycle into two phases. The first part of your cycle is known as the follicular phase. Learn what the LH surge is, how it triggers ovulation, how long it lasts, and how to detect it for optimal conception timing. A surge in LH causes your ovary to release an egg around the second week of each menstrual cycle. A high LH level around this time means that you’re at that moment in your cycle when you’re most likely to get pregnant.