title: Embryo developmental stage at transfer influences outcome of treatment with intracytoplasmic sperm injection.
abstract: OBJECTIVE
  Our purpose was to determine if embryo cell stage at the time of intrauterine transfer correlates with pregnancy rate in patients treated with intracytoplasmic sperm injection (ICSI).
  
  
  METHODS
  We conducted a retrospective analysis of 455 embryo transfer cycles following ICSI and 304 conventional in vitro fertilization (IVF) and embryo transfer cycles in women aged 40 years or less. Abstracted information included grading of the embryo cell stage and quality at the time of transfer.
  
  
  RESULTS
  The overall ICSI pregnancy rate was 30.8%, while that of conventional IVF was 29.3%. However, the ICSI pregnancy rate fell to 9.3% for embryo transfers taking place at the two-cell stage but increased to 35.8% when at least one embryo had more than two cells, and this difference was statistically significant (P < or = 0.0001). The pregnancy rate following conventional IVF was 22.0% when only two-cell embryos were transferred and 32.0% when at least one of the embryos had more than two cells, but this difference in pregnancy rates was not significant (P > 0.05).
  
  
  CONCLUSIONS
  The stage of embryo development at transfer appears to exert a powerful influence on the successful establishment of pregnancy after ICSI.
authors.affiliation: London Gynaecology & Fertility Centre, UK.
authors.forename: J
authors.initials: J
authors.lastname: Zhu
authors.forename: G I
authors.initials: GI
authors.lastname: Meniru
authors.forename: I L
authors.initials: IL
authors.lastname: Craft
mesh_terms: D000328:Adult; D004624:Embryo Transfer; D005314:Embryonic and Fetal Development; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods*; D006801:Humans; D008297:Male; D008845:Microinjections; D011247:Pregnancy; D012189:Retrospective Studies; D013094:Spermatozoa