Luteinizing Hormone (LH) is a hormone produced by the pituitary gland in the brain. In women, LH is responsible for triggering ovulation, the release of a mature egg from the ovary. LH levels surge just before ovulation, causing the release of the egg. This test typically finds the cause of infertility or irregular or stopped menstrual periods. In men, LH stimulates the production of testosterone. This test is often used to identify the cause of infertility or irregular menstrual periods in women, and testosterone deficiency in men.