Day 3 embryo transfer with combined evaluation at the pronuclear and cleavage stages compares favourably with day 5 blastocyst transfer

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Abstract
BACKGROUND: The respective advantages of day 3 and day 5 embryo transfer are a matter of debate. Previous comparisons did not include pronuclear stage zygote scoring and cumulative success rates (fresh and cryopreserved embryos). METHODS: Patients were randomized prospectively for day 3 or day 5 embryo transfer. Day 3 embryos were selected for transfer and cryopreservation by using combined evaluation at the pronuclear and cleavage stages. RESULTS: There was no difference between day 3 and day 5 fresh embryo transfers as to the rates of pregnancy (58 versus 62%), clinical pregnancy (56 versus 58%), delivery (50 versus 48%), implantation (35 versus 38%) and birth (33 versus 36%) rates. The corresponding values for cryopreserved embryo transfers were also similar. However, day 3 embryo transfer compared favourably with day 5 transfer when the pregnancy (90 versus 66%), clinical pregnancy (85 versus 62%) and delivery (77 versus 52%) rates were calculated per oocyte recovery attempt. CONCLUSIONS: With a selected population of good prognosis patients and our embryo selection criteria, the implantation potential of day 3 and day 5 embryos is equal. Per oocyte recovery attempt, day 3 transfer is more clinically efficient than day 5 transfer, but at least one transfer of cryopreserved embryos is necessary to manifest this superiority.