title: [Cryopreservation in blastocyst stage effectively reduce the number of embryos cryopreserved].
abstract: BACKGROUND
  Multiple pregnancies are the main complication associated to assisted reproduction, due to the transfer of more than one embryo. Embryo cryopreservation allows the sequential transfer of all generated embryos, thus diminishing the risk of multiple pregnancies. However, it leads to accumulation of cryopreserved embryos. To reduce their accumulation in our unit, we started to preserve embryos as blastocysts, that have a rate of successful pregnancies of approximately 40%.
  
  
  OBJECTIVE
  To perform a sensitivity analysis of this change of policy on the accumulation of embryos.
  
  
  METHODS
  Records of 571 cycles of in vitro fertilization since 2007 were reviewed, assuming a transference rate of two embryos in women aged less than 35 years and three embryos in older women. The number of embryos that would be preserved as zygotes, eight cell stage or blastocysts, was analyzed.
  
  
  RESULTS
  Multiple component logistic regression analysis showed a 20% reduction in the odds ratio of cryopreservation per year of age. There was a 95% reduction in the ratio, when comparing the preservation of third and first day embryos and a 99% reduction when comparing preservation of embryos in blastocyst stage and first day embryos.
  
  
  CONCLUSIONS
  Cryopreservation at blastocyst stage effectively decreased the frequency of embryo cryopreservation.
authors.affiliation: Unidad de Medicina, Reproductiva de Clínica Monteblanco, Santiago, Chile. jeschwarze@ivf.cl
authors.forename: Juan Enrique
authors.initials: JE
authors.lastname: Schwarze
authors.forename: José
authors.initials: J
authors.lastname: Balmaceda
authors.forename: Ricardo
authors.initials: R
authors.lastname: Pommer
mesh_terms: D000328:Adult; D015925:Cryopreservation / Q000379:methods*; D046149:Embryo Culture Techniques; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods*; D006801:Humans; D011247:Pregnancy; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple; D012189:Retrospective Studies; D013997:Time Factors