title: Efficiency of oocyte cryopreservation: a meta-analysis.
abstract: OBJECTIVE
  To determine the efficiency of oocyte cryopreservation relative to IVF with unfrozen oocytes.
  
  
  METHODS
  Meta-analysis.
  
  
  METHODS
  Academic assisted reproduction center.
  
  
  METHODS
  Results of all reports from January 1997 to June 2005 with the patients undergoing IVF-intracytoplasmic sperm injection (ICSI) with cryopreserved cycles between 1996 and 2004 were compared with those of patients who underwent IVF-ICSI with unfrozen oocytes in 2002 and 2003 in our program.
  
  
  METHODS
  Mean age and number of ET cycles originating from unfrozen oocytes was matched with those for thaw cycles originating from oocytes cryopreserved with a slow-freezing (SF) protocol. Vitrification (VF) reports were not included in the comparative analysis because of a small number of pregnancies (10) before June 2005.
  
  
  METHODS
  The comparison of fertilization rate, clinical pregnancy, and live-birth rates per injected oocyte, clinical pregnancy and live-birth rates per transfer, and implantation rate between IVF-ICSI cycles with frozen and unfrozen oocytes.
  
  
  RESULTS
  Live-birth rates per oocyte thawed were 1.9% and 2.0% for SF and VF, respectively, before June 2005. Live-birth rates per injected oocyte and ET, respectively, were 3.4% and 21.6% for SF and were 6.6% and 60.4% for IVF with unfrozen oocytes. Compared to women who underwent IVF after SF, IVF with unfrozen oocytes resulted in significantly better rates of fertilization (odds ratio [95% confidence interval]); 2.22 (1.80, 2.74), of live birth per injected oocyte; 1.5 (1.26, 1.79), and of implantation; 4.66 (3.93, 5.52). These odds ratios were lower when oocyte cryopreservation success rates from 2002-2004 were compared with those for IVF with unfrozen oocytes. When the reports after June 2005 were considered, this trend did not appear to continue. With the consideration of VF reports after June 2005, however, higher pregnancy rates were achieved.
  
  
  CONCLUSIONS
  In vitro fertilization success rates with slow-frozen oocytes are significantly lower when compared with the case of IVF with unfrozen oocytes. Although oocyte cryopreservation with the SF method appears to be justified for preserving fertility when a medical indication exists, its value for elective applications remains to be determined. Pregnancy rates with VF appear to have improved, but further studies will be needed to determine the efficiency and safety of this technique.
authors.affiliation: Fertility Preservation Program at Center for Reproductive Medicine and Infertility, New York, New York, USA. kuo9001@med.cornell.edu
authors.forename: Kutluk
authors.initials: K
authors.lastname: Oktay
authors.forename: Aylin Pelin
authors.initials: AP
authors.lastname: Cil
authors.forename: Heejung
authors.initials: H
authors.lastname: Bang
mesh_terms: D015925:Cryopreservation / Q000379:methods / Q000706:statistics & numerical data*; D004624:Embryo Transfer / Q000706:statistics & numerical data*; D005260:Female; D005307:Fertilization in Vitro / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D007247:Infertility, Female / Q000453:epidemiology* / Q000628:therapy*; D050498:Live Birth / Q000453:epidemiology*; D009865:Oocytes / Q000637:transplantation*; D017063:Outcome Assessment, Health Care; D011247:Pregnancy; D016896:Treatment Outcome