title: Changes in the freezing protocol for human zygotes alter embryonic development and pregnancy rates.
abstract: OBJECTIVE
  To determine the effect of various freezing protocols on postthaw development and pregnancy rates resulting from transfer of human zygotes.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  Tertiary care center.
  
  
  METHODS
  Couples undergoing assisted reproductive technology (ART) procedures who wished to have their excess zygotes cryopreserved.
  
  
  METHODS
  We cryopreserved zygotes with one of three protocols.
  
  
  METHODS
  Post-thaw survival and development of the zygotes as well as pregnancy rate after transfer of these zygotes.
  
  
  RESULTS
  A 3-minute hold time after seeding, followed by a final preplunging temperature of -180 degrees C, resulted in a clinical pregnancy rate of 28.6%. In contrast, a 15-minute postseed hold time and a -30 degrees C final chamber temperature resulted in a 37.3% clinical pregnancy rate. When we combined the protocols to provide a 15-minute postseed holding time and a -180 degrees C before plunging into liquid nitrogen, we achieved a 69.6% clinical pregnancy rate.
  
  
  CONCLUSIONS
  By increasing the postseeding hold time and decreasing the temperature of the freezing chamber before plunging the zygotes into liquid nitrogen, significant improvements can be made in postthaw development and pregnancy rates.
authors.affiliation: Department of Obstetrics and Gynecology, Greenville Hospital System, South Carolina 29605-5601, USA. bboone@ghs.org
authors.forename: William R
authors.initials: WR
authors.lastname: Boone
authors.forename: Martin M
authors.initials: MM
authors.lastname: Crane
authors.forename: Jane E
authors.initials: JE
authors.lastname: Johnson
authors.forename: H Lee
authors.initials: HL
authors.lastname: Higdon
authors.forename: Dawn W
authors.initials: DW
authors.lastname: Blackhurst
mesh_terms: D000328:Adult; D015925:Cryopreservation; D047108:Embryonic Development; D005260:Female; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy; D018873:Pregnancy Rate; D011446:Prospective Studies; D027724:Reproductive Techniques, Assisted; D015053:Zygote / Q000502:physiology*