Discordance between chorionicity and embryo transfer number: Four cases report and literature review.

OBJECTIVE To report four cases of in vitro fertilization-embryo transfer (IVF-ET) with discordance between chorionicity and embryo transfer number.

DESIGN A case series.

MATERIALS AND RESULTS Four cases underwent ART treatment in Kaohsiung Chang Gung Memorial Hospital between 2018 and 2020: a 34-year-old woman who underwent an IVF-frozen cycle with embryo transfer of one blastocyst and one morula, resulting in a quintuplet pregnancy. The ultrasound of the quintuplets showed four gestational sacs, one of which was a blighted ovum (one empty gestational sac), and one of the remaining three was a monochorionic-monoamniotic twin (MCMA); a 39-year-old woman who underwent an IVF-frozen cycle with the transfer of two blastocysts, resulting in a quintuplet pregnancy. The ultrasound of the quintuplets showed four completely separate chorionic sacs, one of which was a blighted ovum, and one of the remaining three was a monochorionic-diamniotic (MCDA) twin; a 33-year-old woman who underwent an IVF-frozen cycle and a 36-year-old woman who underwent an IVF fresh cycle, both with single blastocyst transfer, resulting in twin pregnancies with two completely separate chorionic sacs with one blighted ovum. Excluding the possibility of spontaneous ovulation and conception and laboratory procedure errors, these four cases demonstrate monozygotic splitting after the blastocyst stage, challenging the existing dogma that only monochorionic can develop after day three post-fertilization.

CONCLUSIONS The accepted theory of monozygotic twinning resulting from the splitting of an embryo per a strict postfertilization timing protocol must be re-examined with the advent of discordance between chorionicity and embryo transfer number. Reducing the number of embryo transfers in IVF treatment is important.