Blastocyst-ET and monozygotic twinning

Purpose: To examine the rate of monozygotic twinning associated with blasto cyst transfer using commercially available, cell-free culture systems with unmanipulated blastocysts. Methods: A retrospective analysis was conducted in multiple private and aca demic infertility centers throughout the United States, of 199 pregnant pat ients following in vitro fertilization (NF) blastocyst embryo transfer (ET) . Human embryos obtained through standard IVF stimulation protocols were cu ltured in commercially available, cell-free media systems and transferred a s blastocysts. The main outcome measure was the rate of monozygotic twinnin g. Results: A total of 199 blastocyst-ET pregnancies were achieved during the study period at the fertility centers examined. Monozygotic twinning was no ted in 10/199 (5%) of these pregnancies. All were monochorionic diamnionic. Conclusions: Monozygotic twinning previously has been reported following IV F; especially in relation to assisted hatching. While blastocyst transfer h as been available for many years using coculture, there have been no publis hed multicenter reports of monozygotic twinning associated with unmanipulat ed blastocysts. In a multicenter analysis a definite increase in monozygoti c twinning was seen following blastocyst-ET. We believe this phenomenon is real and that this information should be considered when counseling patient s for treatment.