A prospective evaluation of cryopreservation strategies in a two-embryo transfer programme (original) (raw)

the elective embryo cryopreservation of all embryos and the 2 To whom correspondence should be addressed transfer of thawed embryos in subsequent cycles (Wada et al., 1992, 1993; Pattinson et al., 1994); (iv) in a donor oocyte A total of 364 consecutive patients requesting in-vitro programme, enabling a second human immunodeficiency virus fertilization (IVF) treatment were divided randomly into antibody test to be performed on the oocyte donor 6 months two groups. In the first group, two embryos in the original later, before the embryos are released from 'quarantine' for IVF cycle were allowed to divide prior to transfer, with any replacement (Hamer et al., 1994); and (v) prior to chemotherapy remaining embryos being cryopreserved at the pronucleate as a means of preserving the patient's future fertility potential (PN) stage. In the second group, all the embryos were (Winkel and Fossum, 1993; Brown et al., 1996). allowed to divide to the early cleavage (EC) stage, and the The use of embryo cryopreservation by IVF units is increasbest two replaced; any suitable remaining embryos were ing rapidly, such that in 1989~700 pregnancies had been frozen at the 2-to 4-cell stage. A total of 134 cycles (36.8%) achieved worldwide (Van Steirteghem and Van Den Abbeel, fulfilled the study criteria for a fresh embryo replacement 1990). Indeed, in 1993 in the UK alone, Ͼ764 live births were and supernumerary embryos cryopreserved. In the PN reported from 6004 frozen-thawed embryo transfers (Human group, 72 out of 182 (39.6%) patients had a fresh embryo Fertilization and Embryology Authority, 1995). replacement accompanied by embryo cryopreservation, The cryopreservation of good quality embryos is generally which was not significantly different from the EC group regarded as being of paramount importance for optimum (62/182; 34.1%). The livebirth rate per fresh embryo embryo survival (Cohen et al., 1986; Mandelbaum et al., transfer in the EC group (17/62; 27.4%) was significantly 1987). However, the stage at which embryos are cryopreserved higher than that for the PN group (8/72; 11.1%; P Ͻ 0.05). varies from clinic to clinic: freezing embryos at the pronuclear Embryo survival following thawing was similar for the PN (PN; Testart et al., 1987; Cohen et al., 1988a,b; Fugger et al., (96/129; 74.4%) and EC (79/102; 77.4%) stages. Although 1988), early cleavage (EC; Lassalle et al., 1985; Freeman not significant, the livebirth rate following the transfer of et al., 1986; Friedler et al., 1988) or blastocyst (Fehilly et al., thawed embryos was higher in the PN group (11/44; 25.0%) 1985) stage all result in a large proportion of the embryos than in the EC group (4/38; 10.5%). Following one fresh surviving the rigours of the freeze-thaw process, and have and two freeze-thaw embryo replacements, the observed resulted in live births. The cryoprotectant used in conjunction cumulative viable pregnancy rates were comparable for with freezing is also stage-specific, with propanediol (PROH; patients in both the PN (40.2%) and EC (41.1%) groups. Mohr and Trounson, 1985), dimethylsulphoxide (DMSO; Key words: cryopreservation/embryo/human Cohen et al., 1985b) or glycerol (Troup et al., 1990) being used for the PN, EC and blastocyst stages respectively of embryo development. Embryos can be frozen in vials, straws