Presumed recurrent monozygotic dichorionic diamniotic twinning following programmed single thawed euploid embryo transfer cycles: a case report.

To our knowledge, this is the first documented case of presumed recurrent monozygotic (MZT) dichorionic diamniotic (DCDA) twin gestations following programmed single thawed euploid embryo transfer (STEET) cycles in an individual who is herself a MZT twin. This report presents a 34-year-old nulligravid female patient and her 33-year-old male partner with unexplained infertility who underwent in vitro fertilization with preimplantation genetic testing for aneuploidy followed by subsequent embryo transfers, resulting in a presumed MZT DCDA twin gestation (STEET #1), a singleton gestation (STEET #2) and a confirmed MZT DCDA twin gestation (STEET#3). Monozygosity was confirmed for the second twin gestation (STEET #3) via single nucleotide polymorphism (SNP)-based cell-free DNA screening; the first twin gestation (STEET#1) is presumed to be MZT with high likelihood given that it resulted from a STEET performed in the setting of confirmed ovulation suppression. Chorionicity was confirmed via first-trimester ultrasound in both twin gestations (STEET #1 and #3). Nevertheless, this case shows that recurrent MZT DCDA twinning may be possible even after single blastocyst transfer and that observed chorionicity may not always conform to traditional twinning. Further research is needed to better understand the mechanisms and predisposing factors underlying MZT twinning as well as the development of DCDA twin gestations after single blastocyst transfers in assisted reproduction. Specific factors contributing to early embryo splitting may relate to the individual person, the embryo cohort or laboratory techniques. Informed consent counseling should include a discussion that MZT DCDA twinning remains a rare but real possibility despite single embryo transfer.