Fig. 2

Study time schedule according to SPIRIT (Standard Protocol Items: Recommendations for Interventional Trials)-t1, pre-study period. t0, allocation. t1, post-allocation period; women allocated to the endometrial scratch will undergo this procedure in the same or next month after randomization, in the luteal phase of the natural cycle (6 to 7 days after a positive ovulation test). t2, 12 months after allocation, at which a follow-up questionnaire will be sent to all women who have completed 12 months of follow-up. t3, period in which follow-up of women with an ongoing pregnancy, within 12 months after randomization, will continue until live birth. t4, close-out period. SAE, severe adverse events