Monozygotic dichorionic-diamniotic pregnancies following single frozen-thawed blastocyst transfer: a retrospective case series

BACKGROUND: The primary aim of the study is to report cases of monozygotic dichorionic-diamniotic (DC-DA) pregnancies after single frozen-thawed blastocyst transfer. METHODS: This is a retrospective case series. All single frozen-thawed blastocyst transfer cycles performed between June 2013 and December 2018 at the Shanghai Ji Ai Genetics and IVF Institute, Obstetrics and Gynecology Hospital, Fudan University, Shanghai, China, were reviewed retrospectively. We included frozen embryo transfer (FET) cycles which clinical pregnancy was confirmed with multiple gestational sacs showed on ultrasonography at around 6 to 7 weeks of gestation. We then conducted an in-depth analysis to further exclude cases which contained newborns of different genders or natural FET cycles. RESULTS: Five thousand four hundred fifteen frozen-thawed single blastocyst transfer cycles were preformed between June 2013 and December 2018 at the Shanghai Ji Ai Genetics and IVF Institute, Obstetrics and Gynecology Hospital, Fudan University, Shanghai, China. Of these, fourteen women underwent a single blastocyst transfer and then achieved clinical pregnancy with an ultrasound diagnosis of multi-chorionic pregnancy. With one natural cycle FET excluded, we finally included thirteen single blastocyst transfer cycles performed in down-regulated controlled FET or hormone replacement FET, in which the possibility of concurrently spontaneous pregnancy was extremely small. These included 13 cases reveal the phenomenon of monozygotic DC-DA twinning after single blastocyst transfer, which challenges the classical theory that only monochorionic pregnancy could happen after 3 days of fertilization. CONCLUSION: This case series suggest that single blastocyst transfer could result DC-DA pregnancies during IVF treatment.