Treating women under 36 years old without top-quality embryos on day 2: a prospective study comparing double embryo transfer with single blastocyst transfer

background: Embryologists currently face a challenge when counselling patients regarding the stage and the number of embryos to transfer when no top-quality embryos (TQE) are available. methods: The aim of this study was to evaluate the efficacy of single blastocyst transfer (SBT) in comparison with the transfer of two cleavage-stage embryos in women under 36 years old. A total of 450 women under 36 years undergoing their first or second IVF treatment who had no TQE on Day 2 were included in this prospective study. Couples were assigned to either a SBT or a double cleavage-stage embryo transfer (DET). The clinical end-points monitored were rates of implantation, delivery and multiple deliveries. results: The rate of transfer was significantly lower for couples assigned to the SBT group compared with the DET group (88 versus 100%, respectively, P , 0.001) while the delivery rate per oocyte retrieval was similar in both groups (26.7%). By contrast, the rate of multiple deliveries was significantly lower in the SBT group compared with the DET group (3.3 versus 23.3%, respectively, P , 0.01). Blastocyst cryopreservation was twice as high in the SBT group compared with the DET group (39 versus 18%, respectively, P , 0.001). conclusions: These findings show the value of extended embryo culture for couples without TQE. In such situations, delaying embryo transfer in order to select a single blastocyst with the highest potential for implantation can reduce the number of multiple pregnancies. Furthermore, our results demonstrate that extended culture allows blastocyst cryopreservation from embryos not available for Day 2 cryopreservation.