Flowchart of the systematic literature search, screening, and study selection. Flow chart describing the systematic search for both published (full articles and conference abstracts) and unpublished trials, and subsequent study selection. ^aPublished as full paper or as a conference abstract. ^bNumber of participants unknown because it is unclear if/how many participants have been included. ^cLimited available data due to various reasons, a.o. closure of one of the centers or withdrawal directly after randomization. ^d13 studies, of which 11 published as full text, 1 published as conference abstract, 1 registered but unpublished. n, number; IPD, individual participant data; AD, aggregate data; ITT, intention to treat; AT, as treated; AT+ET, as treated with embryo transfer; LB, live birth; OP, ongoing pregnancy; CP, clinical pregnancy; BP, biochemical pregnancy.