A prospective evaluation of cryopreservation strategies in a two-embryo transfer programme

A total of 364 consecutive patients requesting in-vitro fertilization (IVF) treatment were divided randomly into two groups. In the first group, two embryos in the original IVF cycle were allowed to divide prior to transfer, with any remaining embryos being cryopreserved at the pronucleate (PN) stage. In the second group, all the embryos were allowed to divide to the early cleavage (EC) stage, and the best two replaced; any suitable remaining embryos were frozen at the 2- to 4-cell stage. A total of 134 cycles (36.8%) fulfilled the study criteria for a fresh embryo replacement and supernumerary embryos cryopreserved. In the PN group, 72 out of 182 (39.6%) patients had a fresh embryo replacement accompanied by embryo cryopreservation, which was not significantly different from the EC group (62/182; 34.1%). The livebirth rate per fresh embryo transfer in the EC group (17/62; 27.4%) was significantly higher than that for the PN group (8/72; 11.1%; P < 0.05). Embryo survival following thawing was similar for the PN (96/129; 74.4%) and EC (79/102; 77.4%) stages. Although not significant, the livebirth rate following the transfer of thawed embryos was higher in the PN group (11/44; 25.0%) than in the EC group (4/38; 10.5%). Following one fresh and two freeze-thaw embryo replacements, the observed cumulative viable pregnancy rates were comparable for patients in both the PN (40.2%) and EC (41.1%) groups.