title: Vitrified-warmed blastocyst transfer cycles yield higher pregnancy and implantation rates compared with fresh blastocyst transfer cycles--time for a new embryo transfer strategy?
abstract: OBJECTIVE
  To compare the clinical outcome of fresh versus vitrified-warmed blastocyst transfer (BT) cycles.
  
  
  METHODS
  Retrospective study.
  
  
  METHODS
  Medical university affiliated hospital.
  
  
  METHODS
  Women aged less than 40 years undergoing BT cycles.
  
  
  METHODS
  Vitrification and warming of blastocyst with the Cryotop system.
  
  
  METHODS
  Clinical pregnancy rate (CPR), implantation rate (IR), and multiple pregnancy rate (MPR).
  
  
  RESULTS
  In 110 fresh BT cycles versus 136 vitrified-warmed BT cycles performed from January 2007 to March 2010, the IR and CPR of vitrified-warmed BT cycles were 37.0% and 55.1%, respectively, which were statistically significantly higher than the corresponding values of 25.2% and 36.4% obtained for fresh BT cycles. Additionally, the MPR was not statistically significantly different between vitrified-warmed and fresh BT cycles when a similar number of blastocysts was transferred to patients.
  
  
  CONCLUSIONS
  Vitrified-warmed BT cycles resulted in statistically significantly higher CPR and IR compared with fresh BT cycles. A new embryo transfer strategy is therefore proposed whereby fresh BT would be avoided in the initial ovarian stimulation cycle. Instead, all the patient's available blastocysts would be vitrified-warmed and transferred in subsequent cycles.
authors.affiliation: IVF Program, Nanjing Maternity and Child Health Hospital, Nanjing Medical University, Jiangsu, People's Republic of China.
authors.forename: Dandan
authors.initials: D
authors.lastname: Zhu
authors.forename: Juanjuan
authors.initials: J
authors.lastname: Zhang
authors.forename: Shanren
authors.initials: S
authors.lastname: Cao
authors.forename: Junqiang
authors.initials: J
authors.lastname: Zhang
authors.forename: Boon Chin
authors.initials: BC
authors.lastname: Heng
authors.forename: Meiling
authors.initials: M
authors.lastname: Huang
authors.forename: Xiufeng
authors.initials: X
authors.lastname: Ling
authors.forename: Tao
authors.initials: T
authors.lastname: Duan
authors.forename: Guo Qing
authors.initials: GQ
authors.lastname: Tong
mesh_terms: D000328:Adult; D001755:Blastocyst; D001831:Body Temperature / Q000502:physiology; D015925:Cryopreservation / Q000379:methods; D010064:Embryo Implantation / Q000502:physiology*; D004624:Embryo Transfer / Q000379:methods* / Q000639:trends; D005260:Female; D006801:Humans; D007246:Infertility / Q000628:therapy*; D010507:Periodicity; D011247:Pregnancy; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple / Q000706:statistics & numerical data; D012189:Retrospective Studies; D013997:Time Factors; D016896:Treatment Outcome; D015854:Up-Regulation