title: Prospective randomized study of two cryopreservation policies avoiding embryo selection: the pronucleate stage leads to a higher cumulative delivery rate than the early cleavage stage.
abstract: OBJECTIVE
  To compare the cumulative live birth rates obtained after cryopreservation of either pronucleate (PN) zygotes or early-cleavage (EC) embryos.
  
  
  METHODS
  Prospective randomized study.
  
  
  METHODS
  University hospital.
  
  
  METHODS
  Three hundred eighty-two patients, involved in an IVF/ICSI program from January 1993 to December 1995, who had their supernumerary embryos cryopreserved either at the PN (group I) or EC (group II) stage. For 89 patients, cryopreservation of EC embryos was canceled because of poor embryo development (group III). Frozen-thawed embryo transfers performed up to December 1998 were considered.
  
  
  METHODS
  Age, oocytes, zygotes, cryopreserved and transferred embryos, damage after thawing, cumulative embryo scores, implantation, and cumulative live birth rates.
  
  
  RESULTS
  The clinical pregnancy and live birth rates were similar in all groups after fresh embryo transfers. Significantly higher implantation (10.5% vs. 5.9%) and pregnancy rates (19.5% vs. 10.9%; P< or = .02 per transfer after cryopreserved embryo transfers were obtained in group I versus group II, leading to higher cumulative pregnancy (55.5% vs. 38.6%; P < or = .002 and live birth rates (46.9% vs. 27.7%; P< or = .0001.
  
  
  CONCLUSIONS
  The transfer of a maximum of three unselected embryos and freezing of all supernumerary PN zygotes can be safely done with significantly higher cumulative pregnancy chances than cryopreserving at a later EC stage.
authors.affiliation: Reproductive Medicine Unit, Department of Gynaecology and Obstetrics, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland. alfred.senn@chuv.hospvd.ch
authors.forename: A
authors.initials: A
authors.lastname: Senn
authors.forename: C
authors.initials: C
authors.lastname: Vozzi
authors.forename: A
authors.initials: A
authors.lastname: Chanson
authors.forename: P
authors.initials: P
authors.lastname: De Grandi
authors.forename: M
authors.initials: M
authors.lastname: Germond
mesh_terms: D000328:Adult; D001723:Birth Rate; D015925:Cryopreservation / Q000379:methods*; D010064:Embryo Implantation; D005260:Female; D006801:Humans; D011247:Pregnancy; D018873:Pregnancy Rate; D011446:Prospective Studies; D017388:Zygote Intrafallopian Transfer