title: Cryo-thawed embryos obtained from conception cycles have double the implantation and pregnancy potential of those from unsuccessful cycles.
abstract: BACKGROUND
  The purpose of this study was to evaluate the influence of fresh IVF/ICSI cycle outcome on the prognosis of the related frozen embryo replacement (FER) cycle.
  
  
  METHODS
  459 FER cycles, involving 2049 cleavage stage embryos with no or up to 10% fragmentation, were performed for which the outcome of the fresh cycle was recorded. The cycles were divided into two groups; group A included cycles in which cryopreserved embryos were obtained from fresh cycles in which conception occurred. Group B were cycles in which cryopreserved embryos originated from unsuccessful fresh cycles.
  
  
  RESULTS
  Groups A and B were comparable with respect to mean (+/- SD) age at cryopreservation (33 +/- 3.9 versus 33.2 +/- 4 years, P = not significant), mean number of oocytes retrieved and fertilized normally in the fresh cycle (11 +/- 5.2 versus 11.2 +/- 4.8, P = not significant) and mean age at the cryo-thawed transfer (34.5 +/- 4.2 versus 33.9 +/- 4 years, P = not significant). No significant difference was found between the two groups with regard to mean number of embryos cryopreserved (6.5 +/- 3.9 versus 6.2 +/- 3.6) and subsequently thawed (4.5 +/- 2.5 versus 4.5 +/- 1.8) per cycle and number of cryo-thawed embryos transferred per cycle (2.0 +/- 0.7 versus 2.1 +/- 0.8). However, the implantation rate per transferred embryo in group A was double that in group B (23 versus 11.2%, P < 0.0001). Moreover, the clinical pregnancy and ongoing pregnancy rates per cycle were significantly higher in group A compared with group B (34.8 and 27.3% versus 15.6 and 13.1%, P < 0.0001 and P = 0.0003 respectively). The difference in FER cycle outcome could not be explained by confounding variables.
  
  
  CONCLUSIONS
  After thawing, cryopreserved embryos originating from conception IVF/ICSI cycles achieve double the implantation and pregnancy rates of those obtained from unsuccessful cycles.
authors.affiliation: Assisted Conception Unit, Guy's and St Thomas' Hospital NHS Trust, St Thomas' Street, London SE1 9RT, UK. tarekeltoukhy@hotmail.com
authors.forename: T
authors.initials: T
authors.lastname: El-Toukhy
authors.forename: Y
authors.initials: Y
authors.lastname: Khalaf
authors.forename: K
authors.initials: K
authors.lastname: Al-Darazi
authors.forename: F
authors.initials: F
authors.lastname: O'Mahony
authors.forename: E
authors.initials: E
authors.lastname: Wharf
authors.forename: A
authors.initials: A
authors.lastname: Taylor
authors.forename: P
authors.initials: P
authors.lastname: Braude
mesh_terms: D000328:Adult; D015925:Cryopreservation; D010064:Embryo Implantation; D004624:Embryo Transfer; D004622:Embryo, Mammalian / Q000502:physiology*; D005260:Female; D005306:Fertilization; D006358:Hot Temperature; D006801:Humans; D011247:Pregnancy; D016896:Treatment Outcome