L’apport de la vitrification dans l’efficience de la fécondation in vitro

Abstract

This work aims to show, from data available in the literature and our own experience, how embryos’ vitrification change and/or improve the management of infertile couples. In all, 652 cycles of frozen-thawed embryo transfers (FET) following vitrification were prospectively included and compared with 1126 FETs from slow freezing (SF) method. Primary end points were the (i) survival rate (SR) (% of embryos with>50% post-thaw intact blastomeres) and (ii) intact survival rate (ISR) (% of embryos with 100% post-thaw intact blastomeres). Secondary end point was the clinical pregnancy rate (CPR) defined as the presence of an intra uterine gestational sac with positive foetal heart beat. In all, 1097 and 2408 embryos have been thawed following vitrification and SF, respectively. We observed a highly significant increase of SR and ISR respectively when thawing concerned vitrified embryos rather than those from SF method (97.0% vs. 72.7%, P<10−4; 91.5% vs. 49.8%, P<10−4). Furthermore, CPR were of 26.5% (73/652) and of 18.1% (204/1126) following FETs performed after vitrification or SF and thawing (P=0.0002), respectively. At the blastocyst stage, ISR was significantly improved following vitrification compared to SF (94.5% vs. 21.4%, P<10−4). In the study period, vitrification (i) reduced the mean number of fresh transferred embryos (1.5 vs. 1.6; P=0.08) and (ii) increased the rate of FETs at the blastocyst stage when compared with the control period (18.1% vs 2.5%., P<10−4). Embryo vitrification preserves all embryos from an ART cycle because of its excellent results regarding ISR at all stages of embryo development. This procedure allows a significant increase of pregnancy rates after thawing. In addition, there is a trend for increasing ART cycles performed using extended culture embryo and vitrification. The expected improvement of the cumulative birth rate at the blastocyst stage following vitrification remains to be demonstrated in a prospective randomized study.