The corpus luteum is formed in an ovary after the egg has been released. It continues to grow for some time after ovulation and produces significant amounts of hormones. The hormones have the side effect of raising the woman's basal body temperature. Tracking your temperature and calculating from the day of the raised temperature to the first day of the next menstrual cycle will give you your luteal phase.
When hormone levels fall, the corpus luteum atrophies, triggering menstruation and the beginning of the next cycle. From the time of ovulation until menstruation begins, the process typically takes about two weeks, with 14 days considered normal. The length of the luteal phase will be fairly consistent from cycle to cycle.
The loss of the corpus luteum can be prevented by fertilization of the egg; the resulting embryo produces human chorionic gonadotropin (hCG), which can preserve the corpus luteum. Because the hormone is unique to the embryo, most pregnancy tests look for the presence of hCG.