Luteal phase defect: part of the infertility zeitgeist or relic from the past?

Luteal phase defect (LPD) or short luteal phase is a controversial entity that has been variously defined over the years. There are a number of potential causes for LPD all of which are associated with inadequate progesterone secretion throughout the luteal phase which impairs endometrial development and is thus thought to cause infertility. However, the relationship between LPD and infertility is complex, with LPD found in both fertile and infertile women. Attempts have been made at treating LPD with a number of regimens including progesterone supplementation and ovulation induction using clomiphene citrate, however, problems with study design have prevented conclusive evidence for the efficacy of these treatments being drawn. Practically, with the more interventionalist and aggressive approaches to managing couples with unexplained infertility, LPD may have become an irrelevant entity.