Top quality embryos at day 2: a prerequisite for single blastocyst transfer? An observational cohort study in women under 36

PURPOSE: While extended culture has been considerably improved, some questions remain regarding the application of Single Blastocyst Transfer (SBT). METHODS: An observational cohort study was undertaken with 456 women under 36 years old and assigned to SBT on a voluntary basis. The main outcome was the cumulative delivery rate per couple according to the number of Top Quality Embryos (TQE) on day 2 (Group 1= > or =2 TQE, Group 2= 1 TQE and Group 3= 0 TQE). RESULTS: Rate of transfer and mean number of frozen blastocyts were higher in Group 1 compared to Group 3. As a consequence, the cumulative delivery rate per couple was higher in Group 1 (47.9%) compared to Group 3 (34.9%). CONCLUSIONS: Single blastocyst transfer combining fresh and frozen cycles, might be a worthwhile strategy irrespective of embryo quality on day 2 providing good delivery rates while keeping the rate of multiple deliveries low.