['To compare the early-cleavage rates and the implantation potential of embryos between the GnRH antagonist and agonist long stimulation protocols in women older than 35 years.', 'Retrospective analysis.', 'Academic medical center.', 'Two hundred twenty patients older than 35 years old underwent IVF.', 'Sixty-eight patients received GnRH antagonist protocol (GnRH antagonist group) and 152 patients received GnRH agonist long stimulation protocol (GnRH agonist group).', 'Early-cleavage rate of zygotes, implantation rate, and pregnancy rate.', 'Early-cleavage rate of zygotes was significantly lower in the GnRH antagonist group than agonist group (21.8% vs. 32.6%, P<.0001). In the GnRH antagonist group, the pregnancy rate was not significantly different between the early-cleavage and late-cleavage subgroups (40.0% vs. 47.4%). In the GnRH agonist group, the pregnancy rate was significantly higher in the early-cleavage subgroup than in the late-cleavage subgroup (61.0% vs. 29.8%, P<.0001).'] Does early cleavage predict treatment outcome following the use of GnRH antagonists in women older than 35?