Influence of group embryo culture strategies on the blastocyst development and pregnancy outcome

To compare two different embryo culture methods and to determine whether grouping embryos based on quality following Day 3 improved outcomes. Two group embryo culture methods were compared in this study. All zygotes were individually cultured from Day 1 to Day 3. On Day 3, embryos were then cultured in group of 2-5 embryos per droplet until Day 5 or 6. The two group culture methods are: A, embryos were randomly grouped regardless of embryo quality; B, good and poor quality embryos were separately grouped. Blastocyst development rate, blastocyst utilization rate, implantation rate and pregnancy rate were detected. The group culture of Day 3 embryos, in which good or poor quality embryos were separately grouped, significantly promoted blastocyst development (61.2 %, 289/472) and blastocyst utilization rate (55.9 %, 264/472) in comparison with those embryos that were randomly grouped for culture regardless of embryo quality (44 %, 177/402 and 41.5 %, 167/402). There was no significant difference in the implantation rate and pregnancy rate between two group culture methods. Grouping of embryos after Day 3 based on embryo quality may benefit blastocyst formation. This may be due to secretion of beneficial factors by good embryos, or removal of detrimental factors from poor embryos. No impacts on pregnancy or implantation outcomes were observed.