Monozygotic Twins and Triplets in Association with Blastocyst Transfer

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Abstract
Purpose : To compare the incidence of monozygotic twins following blastocyst versus day-3 embryo transfer (ET). Methods : A retrospective analysis of the outcome of assisted reproductive technology (ART) cycles utilizing blastocyst ET during 1999–2000 was compared to a similar group of patients undergoing day-3 ET during 1997–1998. Results : Blastocyst ET was used in 75 cycles with 2.0 ± 2 embryos transferred. The comparison group consisted of 90 cycles with day-3 ET and 3.0 ± 2 embryos transferred. Conclusions : High pregnancy rates are maintained with blastocyst ET even though fewer embryos are transferred. The rate of monozygotic twins is higher with blastocyst ET than with day-3 ET. This increase may partially negate the benefit of reduced high-order multiple gestations attributed to blastocyst ET.