Retrospective analysis of outcomes following transfer of previously cryopreserved oocytes, pronuclear zygotes and supernumerary blastocysts

Abstract

Oocyte cryopreservation still bears the experimental label. Remarkable innovation in this field has led to immense improvement in clinical outcomes and has even resulted in outcomes comparable to those achieved following fresh embryo transfers. Such success has prompted this centre to investigate outcomes of cryopreservation options (oocyte versus pronuclear zygote versus supernumerary day-5 blastocyst after fresh embryo transfer). This study retrospectively analysed 200 cryopreservation cycles which were divided into three groups according to cryopreservation option, which were all cultured to blastocyst-stage post thaw/warming from January 2005 to December 2008, and compared them with 400 fresh embryo transfer cycles from the same time period. When compared with fresh embryo transfer, frozen embryo transfers originating from previously cryopreserved oocytes or pronuclear zygotes resulted in similar implantation, pregnancy and live-birth rates; however, frozen embryo transfers originating from supernumerary day-5 blastocysts resulted in lower outcomes. Thus, oocyte and/or pronuclear zygote cryopreservation appear to be the most viable options for women desiring fertility preservation. Cryopreservation of supernumerary blastocysts may lead to a slightly lower live-birth rate since the best-quality blastocysts are generally transferred during the fresh embryo transfer attempt.