Abstract
Worldwide, more than 500,000 assisted reproduction procedures are performed every year. Most of them include pituitary downregulation with gonadotropin-releasing hormone agonists as part of controlled ovarian hyperstimulation. Under this circumstance, luteal support is mandatory and progesterone is the most widely used hormone. Progesterone can be delivered orally, intramuscularly and vaginally. The oral route is the least efficient but the intramuscular route is as efficient as the vaginal route; however, the latter is more acceptable, especially during prolonged treatments, such as oocyte donation and frozen embryo transfer cycles. The purpose of this review is to examine the efficacy and acceptability of different delivery systems and to identify areas where research is needed in order to improve the treatments available today.