The main objective of COS is obtaining an adequate number of good quality oocytes, and also minimize the adverse drug reactions and cycle cancellations due to a high or poor response. The ideal number of oocytes to optimize treatment outcomes has been subject of debate for many years. However, based on recent published data, it seems reasonable to define the optimal number of oocytes to be retrieved after an adequate COS as 10-15 oocytes. To perform an adequate COS, it has been suggested that the antral follicle count (AFC) and anti-müllerian hormone (AMH) are the best biomarkers to predict the ovarian response. Recently, two nomograms have been proposed for the calculation of the follicle stimulating hormone (FSH) starting dose for COS, taking into account different parameters, namely: 1) Age, AFC and day 3 serum FSH; and 2) Age, serum AMH and FSH. Meanwhile, these prediction models are not able to predict an unexpected poor response and also a higher and undesirable ovarian response to FSH monotherapy.