This document discusses luteal phase support in assisted reproductive technology (ART) and recurrent miscarriages. It defines luteal phase defect (LPD) and notes there is no standardized diagnostic test. LPD can cause infertility and recurrent pregnancy loss. Progesterone supplementation is recommended for confirmed LPD, unexplained infertility, advanced maternal age, ART cycles, hyperprolactinemia, and recurrent miscarriages. Progesterone is the preferred drug for luteal phase support as it promotes endometrial development without luteolytic effects. Vaginal progesterone is as effective as intramuscular with fewer side effects and optimal timing and duration of support is from oocyte retrieval/IUI to 9 weeks of gestation.