The test itself measures the level of luteinizing hormone in the urine. As discussed in Woman's Body, the surge of LH during a menstrual cycle triggers the release of a ripened egg from a follicle within the ovaries.
Many women prefer to use their body temperature as a gauge of when they are ovulating.
By taking an oral temperature first thing in the morning, many women can accurately predict their ovulation point. Usually, body temperature rises from .8 to one full degree immediately after an egg has been released. Thus, when the temperature rises, it is a good time to attempt fertilization. Following the prediction of accurate ovulation, many couples employ other techniques to help them conceive children. Some experts, medical and otherwise, suggest the woman keep her pelvis and hips elevated immediately following sexual intercourse.