title: To delay or not to delay a frozen embryo transfer after a failed fresh embryo transfer attempt?
abstract: To evaluate if increasing the interval between a failed fresh embryo transfer and a subsequent frozen embryo transfer (FET) cycle has any effect on clinical pregnancy rates (CPRs).
  
  
  
  Retrospective cohort study.
  
  
  
  University-based tertiary referral center.
  
  
  
  Women who underwent at least one FET after ovarian stimulation for in vitro fertilization (IVF) and a failed fresh embryo transfer attempt from January 2010 to November 2014. We divided our sample according to the "timing" of the first FET (TF-FET), defined by the interval between oocyte retrieval and the FET cycle start date. The start of the FET was classified as either immediate (≤22 days after oocyte retrieval) or delayed (>22 days after oocyte retrieval).
  
  
  
  None.
  
  
  
  CPR after the first FET.
  
  
  
  A total of 1,183 FET cycles (performed in 1,087 women) were included in our study. No significant differences were found between the immediate and delayed FET groups regarding age, number of oocytes retrieved, number of good-quality embryos produced, embryo developmental stage at FET, and number of frozen embryos transferred. Most importantly, the CPRs of the first FET did not differ significantly according to the TF-FET (32.5% after immediate FET vs. 31.7% after delayed FET), even after adjusting for potential confounding with the use of multivariable logistic regression.
  
  
  
  FETs performed immediately after fresh IVF cycles had CPRs similar to those postponed to a later time. Therefore, deferring FETs may unnecessarily prolong time to pregnancy.
authors.affiliation: Center for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium; Department of Obstetrics, Gynecology, and Reproductive Medicine, Santa Maria University Hospital, Lisbon, Portugal. Electronic address: samueldsribeiro@gmail.com.
authors.forename: Samuel
authors.initials: S
authors.lastname: Santos-Ribeiro
authors.affiliation: Center for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Johannie
authors.initials: J
authors.lastname: Siffain
authors.affiliation: Center for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium; Department of Clinical Medicine, Faculty of Health, University of Aarhus, Aarhus, Denmark.
authors.forename: Nikolaos P
authors.initials: NP
authors.lastname: Polyzos
authors.affiliation: Center for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Arne
authors.initials: A
authors.lastname: van de Vijver
authors.affiliation: Center for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Lisbet
authors.initials: L
authors.lastname: van Landuyt
authors.affiliation: Center for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Dominic
authors.initials: D
authors.lastname: Stoop
authors.affiliation: Center for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Herman
authors.initials: H
authors.lastname: Tournaye
authors.affiliation: Center for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Christophe
authors.initials: C
authors.lastname: Blockeel
mesh_terms: D000328:Adult; D015331:Cohort Studies; D015925:Cryopreservation / Q000379:methods*; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D006801:Humans; D007247:Infertility, Female / Q000175:diagnosis / Q000453:epidemiology / Q000628:therapy*; D050498:Live Birth / Q000453:epidemiology; D054315:Oocyte Retrieval / Q000379:methods; D010062:Ovulation Induction / Q000379:methods; D011247:Pregnancy; D012189:Retrospective Studies; D013997:Time Factors; D017211:Treatment Failure
keywords: Frozen embryo transfer; assisted reproduction; embryo cryopreservation; endometrial receptivity; time to pregnancy