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Purpose: To examine the rate of monozygotic twinning associatedwith blastocyst transfer using commercially available,cell-free culture systems with unmanipulated blastocysts.
Methods: A retrospective analysis was conducted in multipleprivate and academic infertility centers throughout theUnited States, of 199 pregnant patients following in vitrofertilization (IVF) blastocyst embryo transfer (ET). Humanembryos obtained through standard IVF stimulation protocolswere cultured in commercially available, cell-free mediasystems and transferred as blastocysts. The main outcomemeasure was the rate of monozygotic twinning.
Results: A total of 199 blastocyst-ET pregnancies wereachieved during the study period at the fertility centersexamined. Monozygotic twinning was noted in 10/199 (5;pc)of these pregnancies. All were monochorionic diamnionic.
Conclusions: Monozygotic twinning previously has beenreported following IVF, especially in relation to assistedhatching. While blastocyst transfer has been available formany years using coculture, there have been no publishedmulticenter reports of monozygotic twinning associated withunmanipulated blastocysts. In a multicenter analysis, a definiteincrease in monozygotic twinning was seen followingblastocyst-ET. We believe this phenomenon is real and thatthis information should be considered when counselingpatients for treatment.