title: Fresh versus frozen embryo transfer: backing clinical decisions with scientific and clinical evidence.
abstract: BACKGROUND
  Improvements in vitrification now make frozen embryo transfers (FETs) a viable alternative to fresh embryo transfer, with reports from observational studies and randomized controlled trials suggesting that: (i) the endometrium in stimulated cycles is not optimally prepared for implantation; (ii) pregnancy rates are increased following FET and (iii) perinatal outcomes are less affected after FET.
  
  
  METHODS
  This review integrates and discusses the available clinical and scientific evidence supporting embryo transfer in a natural cycle.
  
  
  RESULTS
  Laboratory-based studies demonstrate morphological and molecular changes to the endometrium and reduced responsiveness of the endometrium to hCG, resulting from controlled ovarian stimulation. The literature demonstrates reduced endometrial receptivity in controlled ovarian stimulation cycles and supports the clinical observations that FET reduces the risk of ovarian hyperstimulation syndrome and improves outcomes for both the mother and baby.
  
  
  CONCLUSIONS
  This review provides the basis for an evidence-based approach towards changes in routine IVF, which may ultimately result in higher delivery rates of healthier term babies.
authors.affiliation: Uterine Biology, Prince Henry's Institute of Medical Research, Clayton, VIC 3168, Australia Department of Physiology, Monash University, Clayton, VIC 3168, Australia.
authors.forename: Jemma
authors.initials: J
authors.lastname: Evans
authors.affiliation: Uterine Biology, Prince Henry's Institute of Medical Research, Clayton, VIC 3168, Australia Department of Obstetrics and Gynaecology, University of Melbourne, Heidelberg, VIC 3084, Australia.
authors.forename: Natalie J
authors.initials: NJ
authors.lastname: Hannan
authors.affiliation: Uterine Biology, Prince Henry's Institute of Medical Research, Clayton, VIC 3168, Australia.
authors.forename: Tracey A
authors.initials: TA
authors.lastname: Edgell
authors.affiliation: Monash Health, Clayton, VIC 3168, Australia Monash IVF, Clayton, VIC 3168, Australia Department of Obstetrics and Gynaecology, Monash University, Clayton, VIC 3168, Australia.
authors.forename: Beverley J
authors.initials: BJ
authors.lastname: Vollenhoven
authors.affiliation: Monash IVF, Clayton, VIC 3168, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Lutjen
authors.affiliation: Monash Health, Clayton, VIC 3168, Australia Monash IVF, Clayton, VIC 3168, Australia Department of Obstetrics and Gynaecology, Monash University, Clayton, VIC 3168, Australia.
authors.forename: Tiki
authors.initials: T
authors.lastname: Osianlis
authors.affiliation: Uterine Biology, Prince Henry's Institute of Medical Research, Clayton, VIC 3168, Australia Department of Obstetrics and Gynaecology, Monash University, Clayton, VIC 3168, Australia lois.salamonsen@princehenrys.org.
authors.forename: Lois A
authors.initials: LA
authors.lastname: Salamonsen
authors.affiliation: Monash Health, Clayton, VIC 3168, Australia Monash IVF, Clayton, VIC 3168, Australia Department of Obstetrics and Gynaecology, Monash University, Clayton, VIC 3168, Australia.
authors.forename: Luk J F
authors.initials: LJ
authors.lastname: Rombauts
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D015925:Cryopreservation / Q000379:methods*; D010064:Embryo Implantation; D004624:Embryo Transfer / Q000379:methods*; D004717:Endometrium / Q000502:physiology; D019317:Evidence-Based Medicine; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008597:Menstrual Cycle / Q000502:physiology; D016471:Ovarian Hyperstimulation Syndrome / Q000453:epidemiology / Q000517:prevention & control; D011247:Pregnancy; D011256:Pregnancy Outcome
chemical_list: D018952:Antigens, CD34
keywords: IVF success; endometrial receptivity; frozen embryo transfer; human chorionic gonadotrophin; ovarian stimulation