Luteinizing Hormone (LH) is produced by the pituitary gland, a structure at the base of your brain. In the female reproductive system, LH plays a role in menstruation and pregnancy. It signals the ovaries to maintain the menstrual cycle and prepare the body for conception.
LH’s Role in Ovulation
The menstrual cycle is divided into phases: the follicular phase, ovulatory phase, and luteal phase. During the follicular phase, LH, along with follicle-stimulating hormone (FSH), stimulates the growth of ovarian follicles containing eggs. As a dominant follicle matures, it produces increasing amounts of estrogen.
When estrogen levels reach a certain threshold, they trigger a rapid increase in LH secretion from the pituitary gland, known as the LH surge. This surge is the direct signal for ovulation, prompting the mature follicle to rupture and release an egg from the ovary. After the egg is released, the remaining follicle transforms into the corpus luteum, which then produces progesterone to prepare the uterus for a possible pregnancy.
Detecting Your LH Surge
Detecting the LH surge is a practical way to identify the fertile window for conception. Ovulation predictor kits (OPKs) are home urine tests that work by detecting the presence of LH in urine. These kits come with test strips or sticks that change color or display a symbol when an LH surge is detected.
To use OPKs effectively, it is recommended to begin testing a few days before your expected ovulation. For example, if you have a regular 28-day cycle, you might start testing around day 11. A positive result on an OPK means the test line is as dark as or darker than the control line, indicating an LH surge. This surge signals that ovulation is likely to occur within the next 24 to 36 hours.
Interpreting LH Levels for Conception
The “high” LH level that indicates fertility is not a sustained elevated level, but rather a distinct surge. While OPKs provide a qualitative “positive” or “negative” result, blood tests can provide numerical values.
LH levels during the surge can range from 12.2 to 118.0 International Units per Liter (IU/L), though individual variations are common. The most fertile window for conception is during the LH surge and the day immediately following it, as the egg is viable for about 12 to 24 hours after release, and sperm can survive in the reproductive tract for up to five days. This timing is important because the surge indicates impending ovulation, not that ovulation has already happened.
Variations in LH Levels
LH levels can deviate from the typical pattern, affecting fertility. Consistently high LH levels outside of the mid-cycle surge may indicate conditions such as Polycystic Ovary Syndrome (PCOS) or primary ovarian insufficiency. In PCOS, an irregular pattern of gonadotropin-releasing hormone (GnRH) production can lead to elevated LH and irregular periods. Genetic conditions like Turner syndrome can also be associated with high LH levels.
Conversely, consistently low LH levels can suggest issues with the pituitary gland, which may not produce enough LH for sexual development or reproduction. Conditions like hypothalamic amenorrhea, often linked to excessive exercise, stress, or poor nutrition, can cause low LH levels and irregular or absent periods. If you observe unusual or absent LH surges, or have concerns about your LH levels, consulting a healthcare professional is advisable to investigate the cause and discuss management.