Human embryo twinning with applications in reproductive medicine.

Objective: To assess the efficacy of human embryo twinning by blastomere biopsy at different early embryonic stages (splitting efficiency) and to determine the in vitro developmental capacity of twinned human embryos (developmental efficiency).

Design: Randomized comparative study.

Setting: Private IVF centers.

Patient(s): Couples undergoing IVF donating triploid embryos.

Intervention(s): Embryos at the 2- to 5- and 6- to 8-cell stage were split into twin embryos. Half the number of blastomeres from donor embryos were removed and inserted into recipient empty zonae pellucidae. After embryo splitting, donor and recipient embryos were cultured in vitro.

Main Outcome Measure(s): Development of twinned embryos to the blastocyst stage.

Result(s): The number of developing embryos obtained after splitting could be increased in comparison with the number of embryos available before splitting at the 6- to 8-cell stage but not at the 2- to 5-cell stage (splitting efficiency). Splitting of 6- to 8-cell embryos yielded superior rates of twin embryos developing to blastocysts (developmental efficiency). Twinning success was related to the superior morphological quality of embryos used for splitting.

Conclusion(s): This is the first report on twinned human embryos developing to blastocysts. This study exhibits the potential for novel applications in human assisted reproduction.