title: Comparison of perinatal outcomes following fresh and frozen-thawed blastocyst transfer.
abstract: OBJECTIVE
  To investigate the effect of ovarian stimulation on endometrial receptivity by comparing singleton pregnancy and perinatal outcomes following fresh or frozen-thawed blastocyst transfers.
  
  
  METHODS
  A retrospective cohort study enrolled patients undergoing fresh or frozen-thawed blastocyst transfers that resulted in live deliveries between January 1, 2010 and September 30, 2013 at a single academic center. Implantation, clinical pregnancy, spontaneous abortion, and live delivery rates were calculated. The incidence of term delivery, preterm delivery, low birth weight, term low birth weight, and very low birth weight were also recorded. To detect a 10% difference in the implantation rate, a minimum sample size of at least 415 transfer cycles in each group was estimated.
  
  
  RESULTS
  The study included data from 918 fresh and 1273 frozen-thawed cycles. Patients in both groups were of similar age and there was no difference in the grading of blastocysts. No differences were observed in the implantation (37.3% vs 37.7%), clinical pregnancy (50.2% vs 49.4%), spontaneous abortion (7.3% vs 9.3%), and live delivery (42.9% vs 40.6%) rates of the two groups. A sub-analysis of all live singleton and twin deliveries revealed no difference in perinatal outcomes between the two techniques.
  
  
  CONCLUSIONS
  The present study demonstrated equivalent singleton pregnancy and perinatal outcomes when comparing frozen-thawed and fresh blastocyst transfer procedures.
authors.affiliation: Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine, Weill Cornell Medical Center, New York, NY, USA. Electronic address: nip9060@med.cornell.edu.
authors.forename: Nigel
authors.initials: N
authors.lastname: Pereira
authors.affiliation: Department of Obstetrics and Gynecology, Weill Cornell Medical College, New York, NY, USA.
authors.forename: Allison C
authors.initials: AC
authors.lastname: Petrini
authors.affiliation: Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine, Weill Cornell Medical Center, New York, NY, USA.
authors.forename: Jovana P
authors.initials: JP
authors.lastname: Lekovich
authors.affiliation: Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine, Weill Cornell Medical Center, New York, NY, USA.
authors.forename: Glenn L
authors.initials: GL
authors.lastname: Schattman
authors.affiliation: Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine, Weill Cornell Medical Center, New York, NY, USA.
authors.forename: Zev
authors.initials: Z
authors.lastname: Rosenwaks
mesh_terms: D000022:Abortion, Spontaneous / Q000453:epidemiology*; D000328:Adult; D001755:Blastocyst / Q000502:physiology; D015925:Cryopreservation / Q000379:methods*; D036861:Delivery, Obstetric / Q000706:statistics & numerical data*; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods*; D006801:Humans; D007231:Infant, Newborn; D009518:New York; D010062:Ovulation Induction; D036801:Parturition; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D018873:Pregnancy Rate; D012189:Retrospective Studies
keywords: Blastocyst; Fresh embryo transfer; Frozen embryo transfer; In vitro fertilization; Perinatal outcomes; Pregnancy outcomes