title: The importance of number of blastomeres when embryos are transferred in the absence of controlled ovarian hyperstimulation.
abstract: OBJECTIVE
  To determine if the previous findings that transferring embryos with a higher number of blastomeres results in higher pregnancy rates following fresh but not frozen embryo transfer (ET) was related to the use of controlled ovarian hyperstimulation (COH) in the former but not in the latter.
  
  
  METHODS
  Retrospective review of pregnancy and implantation rates following fresh embryo transfer of donor egg recipient cycles (where no COH is used) vs frozen ETs during the same time period according to whether there was at least one embryo with eight blastomeres transferred or not.
  
  
  RESULTS
  Significantly higher pregnancy rates with an 8-cell ET in donor oocyte recipient cycles but not frozen ETs.
  
  
  CONCLUSIONS
  A less favorable uterine environment caused by the use of high dose gonadotropin is not responsible for the once again observed difference in higher pregnancy rates with higher blastomere number in fresh vs frozen ET. However, an effect of the gonadotropin releasing hormone analogue was not ruled out by this study.
authors.affiliation: The University of Medicine and Dentistry of New Jersey, Department of Obstetrics and Gynecology, Division of Reproductive Endocrinology & Infertility, Camden, New Jersey, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Check
authors.forename: D
authors.initials: D
authors.lastname: Summers-Chase
authors.forename: A
authors.initials: A
authors.lastname: Nazari
authors.forename: D
authors.initials: D
authors.lastname: Kiefer
authors.forename: K
authors.initials: K
authors.lastname: Swenson
mesh_terms: D001757:Blastomeres / Q000502:physiology*; D015925:Cryopreservation; D010064:Embryo Implantation; D004624:Embryo Transfer; D005260:Female; D006801:Humans; D010062:Ovulation Induction; D011247:Pregnancy; D018873:Pregnancy Rate; D012189:Retrospective Studies