Human embryo twinning with proof of monozygocity

To prove monozygocity of human twin blastocysts derived from embryo splitting at the cleavage stage. Human triploid embryos at the 6–8 cell stage were split into twin embryos (D and R) and cultured in vitro to the blastocyst stage. Twin embryos were processed for nested multiplex PCR using fluorescently labeled primers of six selected polymorphic STR markers within the human HLA locus. A total of 11 pairs of twin embryos were analyzed with PCR technology. From five pairs of twin blastocysts, the fluorograms provided detectable STR profiles for identical peak position between the twin embryos. This is the first report on twinned human embryos to prove monozygocity at the DNA level. Embryo splitting exhibits novel potential for future applications in assisted reproductive medicine.