Down-regulation for 28 days prior to transfer is one of the down-regulation protocols, which is designed to synchronize follicular development and endometrial thickness with that of the pre-transfer embryo, making it more conducive to transfer. The 28-day down-regulation is usually done by injecting long-acting GnRH-a (gonadotropin-releasing hormone)-like drugs on the 1st to 2nd day of menstruation, which effectively inhibits the pituitary gland’s secretion of gonadotropins, and during the process of administering the medication, it can synchronize the follicle development, improve the endometrium’s tolerance, and reduce the inflammatory factors in the pelvis. The 28-day period is favorable for the hormones and the endometrium to reach the standard, which facilitates the transfer. There are many options for down regulation before embryo transfer, including GnRH-a Long, Short, Ultra Short, and Early Follicular Phase Long GnRH-a Long, and the duration of down regulation varies from one option to another. If you need to down-regulate before transplantation, it is recommended to follow the instructions of your hospital’s Assisted Reproductive Medicine doctor and have regular hospital checkups.