Abstract The synchronization of the donor stimulation with the endometrial preparation of the recipient is usually done by downregulating the recipient's pituitary with a GnRH analog. Objective The aim of this study is to compare pregnancy and implantation rates among premenopausal oocyte recipients synchronized by pituitary suppression with GnRH agonist (Group AGO) or antagonist (Group ANTAG) and standard endometrial preparation with estrogen and gestagen. Study design Prospective, observational, transversal, comparative study. Consecutive recipients treated at Institut Universitari Dexeus between July 2008 and December 2009. Results One hundred and eighty-three premenopausal women were included. No differences were found regarding the age of donors nor the age of recipients, fertilization rates, number of embryos transferred and embryo quality. No differences were found in clinical pregnancy rates (56.1% Group AGO vs. 52.4% Group ANTAG). Conclusion The administration of GnRH antagonists during endometrial preparation in oocyte recipients facilitates synchronization without affecting the pregnancy rate.