During IVF cycles an embryo is generally placed into the uterine cavity between 3 and 5 days after fertilization. For a successful pregnancy to take place, that embryo must then implant in the properly primed and staged endometrium, which subsequently must continue to develop to accommodate the growing and maturing embryo and then fetus. This process is normally regulated by hormonal interactions between the fetal, endometrial and luteal tissue. It has been found that after IVF additional support for the endometrium with progesterone improves implantation and subsequent live birth rates in IVF cycle . Recent data has shown that additional supplementation with a single administration of a GnRH agonist around the time the time of embryo transfer may further enhance these rates .