Many years have passed since GnRH antagonists were introduced to prevent premature LH surges during stimulated cycles. However, there is still no consensus on the optimal GnRH antagonist protocol. Attempts at modifying GnRH antagonist protocols have been made to improve COH outcomes. However, a meta-analysis of 27 randomized controlled trials, including recent reports, showed significantly lower clinical ongoing pregnancy rates in the antagonist group. Thus, additional efforts are needed to identify the optimal stimulation protocols to achieve better follicular and embryonic development and to improve the pregnancy rates in COH using GnRH antagonist.