Within OB/GYN residency training, there is a gap in knowledge and competence in the reproductive endocrinology and infertility (REI) subspecialty, noted both on resident and post-graduate surveys at our institution as well as nationally. There is currently only one published REI curriculum, and the medical information covered is now outdated. To review this information, and improve retention and applicability for a population of OB/GYN residents, we sought to teach the menstrual cycle backwards using interactive, small group sessions reviewing multiple brief clinical cases to teach and reinforce the physiology.