Abstract
Progesterone production from the corpus luteum is critical for natural reproduction. Progesterone supplementation seems to be an important aspect of any assisted reproductive technology treatment. Luteal phase deficiency in natural cycles is a plausible cause of infertility and pregnancy loss, though there is no adequate diagnostic test. This article describes the normal luteal phase of the menstrual cycle, investigates the controversy surrounding luteal phase deficiency, and presents the current literature for progesterone supplementation during assisted reproductive technologies.