Luteal phase support for assisted reproductive technologies: between past, present and future.

The luteal phase is defined as the period between ovulation and either the establishment of a pregnancy or the onset of menses two weeks later. Assisted reproductive technologies (ART), and in particular controlled ovarian stimulation (COS), negatively interfere with the endocrine mechanisms normally regulating the luteal phase. Up to now, there is no generally accepted opinion as to the most appropriate therapeutic schemes for luteal phase support in ART cycles. Progesterone-based protocols are the most frequently adopted, while alternative regimens including human chorionic gonadotropin (hCG) and GnRH agonists (GnRH-a) are controversial. A GnRH-a can be used instead of hCG for ovulation triggering and the effectiveness of luteal phase support in such new protocols is the object of a growing number of experimental studies. Currently, vaginal progesterone is considered as the first line therapy for luteal phase support (LPS). The starting-time and the duration of luteal phase supplementation after the onset of pregnancy are still debated. Despite the lack of clinical or biological evidence supporting the efficacy of luteal phase support in intrauterine insemination cycles, the use of progesterone has become a well-established practice.