title: Delayed blastocyst development does not influence the outcome of frozen-thawed transfer cycles.
abstract: OBJECTIVE
  To compare the outcome of transfer of thawed blastocysts frozen on either day 5 or day 6 after in vitro fertilisation.
  
  
  METHODS
  Cohort observational study.
  
  
  METHODS
  Tertiary assisted conception unit in London, UK.
  
  
  METHODS
  Six hundred and forty-two consecutive nondonor programmed thawed blastocyst transfer (TBT) cycles.
  
  
  METHODS
  High-grade blastocysts were frozen on day 5 (n = 314) or day 6 (n = 328) after fertilisation using a slow-freezing protocol. Endometrial preparation was performed using estradiol valerate. Progesterone supplementation was commenced when the endometrial thickness had reached 7 mm or more. Frozen blastocysts were thawed on day 6 of progesterone supplementation and assessed immediately after thawing for survival, and after 3-4 hours for blastocoele re-expansion. Main outcome measures Thawed blastocyst survival and re-expansion rates, and pregnancy and live birth rates, per TBT.
  
  
  RESULTS
  Thawed blastocyst survival and re-expansion rates were comparable between the day 5 and day 6 groups (87% versus 87%, P = 0.50 and 73% versus 71%, P = 0.35, respectively). The live birth rate was similar between the two groups (29% versus 28.5%, P = 0.93, respectively). After adjusting for confounding variables, the odds ratio (OR) of a live birth in cycles in which the thawed blastocysts were frozen on day 6 compared with day 5 was 1.23 [95% confidence interval (CI), 0.81-1.86, P = 0.34].
  
  
  CONCLUSIONS
  The pregnancy potential of high-grade blastocysts frozen on day 5 and day 6 after in vitro fertilisation and replaced in programmed TBT cycles is comparable.
authors: Assisted Conception Unit, Guy's and St. Thomas' Hospital NHS Foundation Trust, London, UK. tarek.el-toukhy@gstt.nhs.uk
authors: T
authors: T
authors: El-Toukhy
authors: E
authors: E
authors: Wharf
authors: R
authors: R
authors: Walavalkar
authors: A
authors: A
authors: Singh
authors: V
authors: V
authors: Bolton
authors: Y
authors: Y
authors: Khalaf
authors: P
authors: P
authors: Braude
mesh_terms: D000328:Adult; D001755:Blastocyst / Q000166:cytology*; D002470:Cell Survival; D015925:Cryopreservation / Q000379:methods; D010064:Embryo Implantation / Q000502:physiology*; D004624:Embryo Transfer / Q000379:methods*; D047108:Embryonic Development; D004958:Estradiol / Q000031:analogs & derivatives / Q000627:therapeutic use; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods*; D006801:Humans; D007247:Infertility, Female / Q000628:therapy; D007248:Infertility, Male / Q000628:therapy*; D050498:Live Birth; D008297:Male; D011247:Pregnancy; D011256:Pregnancy Outcome; D018873:Pregnancy Rate; D011374:Progesterone / Q000627:therapeutic use; D011372:Progestins / Q000627:therapeutic use; D013997:Time Factors
chemical_list: D011372:Progestins; D011374:Progesterone; D004958:Estradiol