title: Should embryos developing to blastocysts on day 7 be cryopreserved and transferred: an analysis of pregnancy and implantation rates.
abstract: OBJECTIVE
  To compare pregnancy rates (PRs) using blastocysts cryopreserved on day 7 with those cryopreserved on days 5 and 6.
  
  
  METHODS
  Retrospective observational cohort study.
  
  
  METHODS
  Infertility center performing IVF.
  
  
  METHODS
  Eight hundred women with infertility undergoing frozen ET.
  
  
  METHODS
  Blastocysts cryopreserved on days 5, 6, and 7 after retrieval were thawed and transferred.
  
  
  METHODS
  Ongoing PRs (pregnancy developing appropriately into the second trimester). Thaw survival, implantation rates, and clinical PRs were also calculated.
  
  
  RESULTS
  A total of 1,406 embryos were thawed with a survival of 90.7% for day 5, 83.7% for day 6, and 78.7% for day 7. Implantation rates were 43.3%, 28.9%, and 28.9%, respectively. Ongoing PRs were 43.9%, 32.9%, and 26.7%, respectively.
  
  
  CONCLUSIONS
  Blastocysts cryopreserved on day 7 have a lower, but clinically important potential. Embryos that do not achieve blastocyst stage on day 6 should not be universally discarded, but should be observed in culture 1 more day as 27% may result in an ongoing pregnancy.
authors.affiliation: Reproductive Associates of Delaware, Newark, Delaware. Electronic address: gkovalevsky@gmail.com.
authors.forename: George
authors.initials: G
authors.lastname: Kovalevsky
authors.forename: Stacy M
authors.initials: SM
authors.lastname: Carney
authors.forename: Linda S
authors.initials: LS
authors.lastname: Morrison
authors.forename: Caitlin F
authors.initials: CF
authors.lastname: Boylan
authors.forename: Adrienne B
authors.initials: AB
authors.lastname: Neithardt
authors.forename: Ronald F
authors.initials: RF
authors.lastname: Feinberg
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001755:Blastocyst; D016009:Chi-Square Distribution; D015925:Cryopreservation; D046149:Embryo Culture Techniques; D010064:Embryo Implantation; D004624:Embryo Transfer / Q000009:adverse effects; D005260:Female; D005298:Fertility; D005307:Fertilization in Vitro / Q000009:adverse effects; D006801:Humans; D007247:Infertility, Female / Q000503:physiopathology / Q000628:therapy*; D011247:Pregnancy; D018873:Pregnancy Rate; D012189:Retrospective Studies; D013997:Time Factors; D016896:Treatment Outcome
keywords: Frozen embryo transfer; blastocyst; day 7 blastocysts