Fig. 1

Comparison of recruitment rates between re-randomization and parallel-group designs in in vitro fertilization (IVF) trials. *PG parallel-group, RR re-randomization. The red line denotes recruitment for a parallel-group trial. The blue line denotes recruitment for a re-randomization trial where each participant may be enrolled for a maximum of two treatment cycles. The green line denotes recruitment for a re-randomization design where each participant may be enrolled for a maximum of three treatment cycles. The dotted line denotes the sample size target. For the re-randomization designs, treatment cycles were 6 months apart. Panel a denotes a small trial (n = 564) with a short recruitment duration (21 months). Panel b denotes a small trial (n = 564) with a long recruitment duration (55 months). Panel c denotes a large trial (n = 3730) with a short recruitment duration (21 months). Panel d denotes a large trial (n = 3730) with a long recruitment duration (55 months)