title: Embryo transfer is equally effective at cleavage stage and blastocyst stage: a randomized prospective study.
abstract: OBJECTIVE
  To compare the implantation and pregnancy rates after cleavage stage embryo transfer (ET) with transfer of blastocyst-stage (days 5-6) embryos.
  
  
  METHODS
  Prospective randomized trial at an assisted reproduction unit in a university hospital. Women with six or more follicles at the last ultrasound scan before oocyte aspiration were randomized for transfer of a maximum of two embryos after 2-3 days (n = 80) or after 5-6 days (n = 64) of culture. Embryo quality, implantation and pregnancy rates were evaluated. Statistical significance was tested with the Chi-square test and Fisher's exact test.
  
  
  RESULTS
  No significant difference was observed in implantation rates (21.1% versus 20.9%, respectively) and clinical pregnancy rates (36.7% versus 32.5% respectively) after blastocyst and cleavage stage transfers for the two groups. The pregnancy rate among subjects who had at least one good quality embryo transferred was 37.5% per day 2-3 ET and 60% per day 5-6 ET.
  
  
  CONCLUSIONS
  The overall implantation and pregnancy rates after embryo transfer at cleavage stage and at blastocyst stage transfer were not statistically different. Women who had at least one good quality blastocyst (n = 25) had a high pregnancy rate (60% per ET). Blastocyst transfer is a good alternative for couples with many good quality embryos on day 2 after insemination.
authors.affiliation: Department of Obstetrics and Gynaecology, Karolinska Institutet, Karolinska University Hospital Huddinge, Fertility Unit K-59, Halsovagen, S-14186 Stockholm, Sweden. julius.hreinsson@kus.se
authors.forename: Julius
authors.initials: J
authors.lastname: Hreinsson
authors.forename: Björn
authors.initials: B
authors.lastname: Rosenlund
authors.forename: Margareta
authors.initials: M
authors.lastname: Fridström
authors.forename: Ingvar
authors.initials: I
authors.lastname: Ek
authors.forename: Lev
authors.initials: L
authors.lastname: Levkov
authors.forename: Peter
authors.initials: P
authors.lastname: Sjöblom
authors.forename: Outi
authors.initials: O
authors.lastname: Hovatta
mesh_terms: D000328:Adult; D001755:Blastocyst; D002970:Cleavage Stage, Ovum; D010064:Embryo Implantation; D004624:Embryo Transfer; D005260:Female; D006801:Humans; D011247:Pregnancy; D018873:Pregnancy Rate; D011446:Prospective Studies