title: Slow freezing, vitrification and ultra-rapid freezing of human embryos: a systematic review and meta-analysis.
abstract: Embryo cryopreservation is an important aspect of assisted reproduction. Many methods have been described, but they have been poorly investigated in randomized trials, highlighting the need for a systematic review of the literature. Meticulous electronic/hand searches were performed to locate randomized trials (RCT) comparing embryo cryopreservation methods. Primary outcomes were clinical pregnancy rate (CPR) and incidence of congenital abnormalities. Secondary outcomes included live-birth (LBR), ongoing pregnancy (OPR), implantation (IR), and miscarriage (MR) rates. Data were extracted to allow for an intention-to-treat analysis and analysed using a random-effects model. Literature search revealed 11 RCT, of which five were excluded. The quality of the included studies was variable, but generally poor. There was a significantly higher CPR, OPR and IR with vitrification compared with slow freezing (odds ratio (OR)=1.55, 95% confidence interval (CI)=1.03-2.32, OR=1.82, 95% CI=1.04-3.20 and OR=1.49, 95% CI=1.03-2.15, respectively). In addition, there was a significantly lower CPR and OPR with embryo ultra-rapid freezing compared with slow freezing (OR=0.35, 95% CI=0.16-0.76 and OR=0.37, 95% CI=0.17-0.81, respectively). Vitrification is superior to slow freezing, which in turn is superior to ultra-rapid freezing. However, more well-designed and powered studies are needed to further corroborate these findings.
authors.affiliation: Department of Obstetrics and Gynecology, Cleveland Clinic Foundation, Cleveland, OH, USA.
authors.forename: Faten F
authors.initials: FF
authors.lastname: AbdelHafez
authors.forename: Nina
authors.initials: N
authors.lastname: Desai
authors.forename: Ahmed M
authors.initials: AM
authors.lastname: Abou-Setta
authors.forename: Tommaso
authors.initials: T
authors.lastname: Falcone
authors.forename: James
authors.initials: J
authors.lastname: Goldfarb
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology; D000013:Congenital Abnormalities / Q000453:epidemiology; D015925:Cryopreservation / Q000379:methods*; D010064:Embryo Implantation; D004622:Embryo, Mammalian; D005260:Female; D006801:Humans; D008297:Male; D011247:Pregnancy; D018873:Pregnancy Rate; D016032:Randomized Controlled Trials as Topic