title: A randomized comparison of the cryopreservation of one-cell human embryos with a slow controlled-rate cooling procedure or a rapid cooling procedure by direct plunging into liquid nitrogen.
abstract: We conducted a randomized prospective study of the cryopreservation of one-cell human embryos, comparing a slow controlled-rate freezing procedure with a rapid cooling procedure by direct plunging into liquid nitrogen. We analysed the numbers of embryos that were recovered immediately after thawing (= recovery), the number of embryos morphologically intact after thawing and subsequent dilution of the cryoprotectants (= survival), the numbers of embryos undergoing further cleavage after 24 h of in-vitro culture (= cleavage) and the implantation of transferred embryos (= children born per frozen-thawed embryo transferred). We demonstrated that the recovery of embryos was greater after slow controlled-rate freezing. Survival was greater after rapid cooling and the number of embryos undergoing further cleavage was higher after slow controlled-rate freezing. Although the birth rate was twice as high after slow controlled-rate freezing as after rapid cooling, this difference was not statistically significant. In conclusion, our results show clearly that for the freezing of one-cell human embryos, slow controlled-rate freezing is more efficient than rapid cooling. Before rapid cooling is used routinely in clinical in-vitro fertilization programmes, its safety and reproducibility must be convincingly demonstrated.
authors.affiliation: Centre for Reproductive Medicine, University Hospital and Medical School, Dutch-speaking Brussels Free University (Vrije Universiteit Brussel), Belgium.
authors.forename: E
authors.initials: E
authors.lastname: Van den Abbeel
authors.forename: M
authors.initials: M
authors.lastname: Camus
authors.forename: L
authors.initials: L
authors.lastname: Van Waesberghe
authors.forename: P
authors.initials: P
authors.lastname: Devroey
authors.forename: A C
authors.initials: AC
authors.lastname: Van Steirteghem
mesh_terms: D002970:Cleavage Stage, Ovum; D015925:Cryopreservation / Q000379:methods*; D010064:Embryo Implantation; D004624:Embryo Transfer; D004622:Embryo, Mammalian / Q000502:physiology*; D005260:Female; D015181:Gamete Intrafallopian Transfer; D006801:Humans; D009584:Nitrogen; D011247:Pregnancy; D011446:Prospective Studies; D013997:Time Factors
chemical_list: D009584:Nitrogen