A Luteinizing Hormone (LH) chart is a visual record of daily hormone levels used to predict ovulation and identify the most fertile days in a menstrual cycle. This tracking method, often done using over-the-counter ovulation predictor kits (OPKs), detects the sharp increase in LH that signals the body is preparing to release an egg. Understanding the typical pattern of a normal LH chart is a powerful tool for anyone tracking their reproductive health. The chart translates complex hormonal shifts into a simple, readable pattern, allowing for precise timing.
The Role of Luteinizing Hormone in the Cycle
Luteinizing hormone (LH) is a reproductive hormone produced and released by the pituitary gland. Throughout the first half of the menstrual cycle, LH works alongside Follicle-Stimulating Hormone (FSH) to encourage the growth of ovarian follicles. As these follicles mature, they produce increasing amounts of estrogen, which acts as a hormonal signal.
The rising estrogen triggers a dramatic shift, causing the pituitary gland to release a large, rapid burst of LH into the bloodstream, known as the LH surge. This surge is the biological command that triggers the final maturation and release of the egg from the ovary (ovulation). Ovulation typically occurs about 24 to 36 hours after the onset of the LH surge.
After the egg is released, LH stimulates the remaining follicle tissue to transform into the corpus luteum. The corpus luteum produces progesterone, a hormone necessary to prepare the uterine lining for a potential pregnancy. If pregnancy does not occur, LH levels quickly decrease back to their baseline, signaling the cycle to restart.
Defining the Normal LH Chart Pattern
A normal LH chart is characterized by a distinct shape that resembles a mountain peak. For the majority of the follicular phase leading up to ovulation, LH levels remain low and consistent. These low readings form the stable baseline of the chart, often showing only a very faint test line on an OPK.
The main feature of a normal chart is the surge itself, which appears as a sharp, rapid spike in concentration. This dramatic rise is short-lived, with the entire surge lasting only about 24 to 48 hours in many women. The single highest measurement during this time is referred to as the LH peak.
Following the peak, the chart shows an equally rapid decline as LH levels return to the low levels seen during the luteal phase. This clear progression—low baseline, sharp spike, and swift drop—is the classic “single surge pattern.” The visual clarity of this pattern, where the test line becomes as dark as or darker than the control line, allows users to confidently predict the most fertile window.
Practical Charting and Testing Methodology
Achieving a clear LH chart depends on consistent and correct testing methodology. The timing of testing is important because LH surges often begin in the early morning and take a few hours to register in the urine. Using first-morning urine is generally not recommended, as it can cause the surge to be missed. The optimal time to test is typically in the afternoon, between 10 a.m. and 8 p.m.
The test should be performed at approximately the same time each day. Users should also limit fluid intake for about two hours prior to testing to prevent the urine from becoming overly diluted. Diluted urine can lower the concentration of LH, potentially leading to a false-negative result even when a surge is occurring.
The day to begin testing is determined by the length of the individual’s cycle. A common guideline is to start testing 17 days before the expected start of the next period. For example, in a 28-day cycle, testing would begin on Day 11. Tracking the daily results on a paper chart or a digital application helps visualize the progression from low to high levels.
Common Variations and Atypical Results
While the single, sharp spike is the most common pattern, LH charts can exhibit several normal variations. Some women experience a “gradual onset” or “stair-step” increase, where LH levels slowly rise over two to six days before reaching the peak. This contrasts with the “rapid onset” surge, which peaks quickly, sometimes in less than a day. Women with rapid surges may need to test twice daily to avoid missing the brief peak.
Another variation is the appearance of multiple peaks, known as a biphasic or double surge. This pattern involves an initial rise in LH that does not lead to ovulation, followed by a second, true surge several days later. If a cycle is anovulatory, the chart may show a long, flat line of low LH readings, suggesting the hormonal signal required to trigger ovulation was never sent.
Consistently irregular or flat lines, particularly in women with irregular cycles, may indicate an underlying issue such as Polycystic Ovary Syndrome (PCOS). In these cases, the body may attempt to ovulate multiple times without success, causing fluctuating LH levels that make charting difficult. If a person consistently tracks flat lines or confusing, multiple surges, consulting a healthcare professional is recommended.