title: Frozen-thawed embryo transfer: influence of clinical factors on implantation rate and risk of multiple conception.
abstract: BACKGROUND
  Frozen embryo transfer is an important supplementary procedure in the treatment of infertility. While general information concerning the outcome of frozen embryo transfer has been documented, few studies have addressed the potential of embryo implantation in particular clinical situations. Importantly, the risk of multiple conception following frozen embryo transfer has been poorly documented compared with the information available for fresh embryo transfer.
  
  
  METHODS
  This is a retrospective study analysing 3570 frozen embryo transfer cycles (1438 couples) with a view to increasing our understanding of the clinical circumstances that influence the potential for embryo implantation.
  
  
  RESULTS
  The overall implantation rate was 9.1%. The characteristics associated with a more favourable implantation rate were the success of the previous fresh embryo transfer cycle, age < 40 years and non-tubal factor aetiology of infertility. Such women had an increased risk of multiple conception.
  
  
  CONCLUSIONS
  Female age, the aetiology of infertility and the outcome of fresh embryo transfer are the most important factors influencing the implantation rate following frozen embryo transfer. A prognostic table has been constructed that may assist with the determination of the optimal number of embryos to be replaced in frozen embryo transfer to provide better individualized counselling and to secure an optimal chance of pregnancy while reducing the risk of multiple conception.
authors.affiliation: Reproductive Medicine Unit, Department of Obstetrics and Gynaecology, The University of Adelaide, The Queen Elizabeth Hospital, 28 Woodville Road, Woodville, South Australia 5011, Australia. jim.wang@adelaide.edu.au
authors.forename: J X
authors.initials: JX
authors.lastname: Wang
authors.forename: Y Y
authors.initials: YY
authors.lastname: Yap
authors.forename: C D
authors.initials: CD
authors.lastname: Matthews
mesh_terms: D000328:Adult; D000375:Aging; D015331:Cohort Studies; D015925:Cryopreservation; D010064:Embryo Implantation; D004624:Embryo Transfer; D005260:Female; D006801:Humans; D007246:Infertility / Q000209:etiology; D008875:Middle Aged; D011247:Pregnancy; D011272:Pregnancy, Multiple; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors