Intramuscular progesterone optimizes live birth from programmed frozen embryo transfer: a randomized clinical trial

To determine whether vaginal progesterone for programmed endometrial preparation is noninferior to intramuscular progesterone in terms of live birth rates from frozen embryo transfer (FET). Three-armed, randomized, controlled noninferiority trial. Multicenter fertility clinic. A total of 1,346 volunteer subjects planning vitrified-warmed transfer of high-quality nonbiopsied blastocysts were screened, of whom 1,125 subjects were ultimately enrolled and randomly assigned to treatment.