Figure 1

Flow-chart of the selection phase. Overall, more than half of the eligible women could not be informative because they did not fullfill our selection criteria (109 out of 199). The most common reason for exclusion was the referral in the early menstrual cycle phase (N = 31), the absence of dominant follicles or corpora lutea at basal ultrasound (N = 22) and the assumption of oral contraceptives (N = 20).