Aim of the study was to evaluate the reached spot and also rate of increment for serum FSH levels on the antagonist started day between patients with different COH responses (poor, suboptimal response or normo-responders) stimulated with a high (300 IU) fixed rFSH dose during antagonist cycles. Retrospective cross-sectional cohort study conducted in an University ART Center. Totally 122 women were evaluated, among them 51 were poor responders, 52 had suboptimal response and 19 had normal response. Primary outcome measure was the serum FSH levels on the day of first GnRH antagonist dose administrated and rate of increment in serum FSH (which is calculated as ; serum FSH level on the day of first GnRH antagonist dose administrated – CD2 serum FSH level / CD2 serum FSH level x100, and expressed as a percentage). Secondary outcomes were correlations between rate of increment in serum FSH and cycle outcomes (retrieved oocyte number and the rate of COH response, P and E2 levels on hCG trigger day). The rate of response to COH was calculated as; retrieved oocyte number / AFC x 100 and expressed as a percentage. The rate of response to COH should be evaluated as a clinical performance indicator as many parameters which had been evaluated as laboratory indicators in the Vienna consensus. Basal serum FSH levels differed significantly between all three groups (7[5.2-8.6], 5.7[4.6-7.2], 4.8[4.1-5.3] in poor, suboptimal and normal response groups respectively; p<0.001). Median spot serum FSH levels on the antagonist starting day was significantly lower in the normo responders than poor and suboptimal response groups (p=0.001 and p=0.025). Rate of increment in serum FSH levels till to the antagonist starting day did not differ significantly between groups (p=0.39). Rate of response to COH was significantly higher for the normoresponder group compared to poor and suboptimal groups (p<0.001 and p=0.019). Rate of increment in serum FSH levels till to the antagonist starting day was positively correlated with the response to COH (r=0.24, p=0.008). Although rate of increment from the initial for serum FSH levels did not differ between groups, normoresponder patients had a higher rate of response to COH. Also, these findings support that; poor responders have limited pool of small antral follicles which already advanced due to higher initial FSH levels and may not benefit from higher FSH starting doses. [ABSTRACT FROM AUTHOR]