title: A retrospective study of single frozen-thawed blastocyst transfer.
abstract: OBJECTIVE
  To study the clinical outcomes of single frozen-thawed blastocyst transfer cycles according to the hatching status of frozen-thawed blastocysts.
  
  
  METHODS
  Frozen-thawed blastocysts were divided into three groups according to their hatching status as follows: less-than-expanded blastocyst (≤EdB), hatching blastocyst (HgB), and hatched blastocyst (HdB). The female age and infertility factors of each group were evaluated. The quality of the single frozen-thawed blastocyst was also graded as grade A, tightly packed inner cell mass (ICM) and many cells organized in the trophectoderm epithelium (TE); grade B, several and loose ICM and TE; and grade C, very few ICM and a few cells in the TE. The clinical pregnancy and implantation rate were compared between each group. The data were analyzed by either t-test or chi-square analysis.
  
  
  RESULTS
  There were no statistically significant differences in average female ages, infertility factors, or the distribution of blastocyst grades A, B, and C in each group. There was no significant difference in the clinical pregnancy and implantation rate of each group according to their blastocyst grade. However, there was a significant difference in the clinical pregnancy and implantation rate between each group. In the HdB group, the clinical pregnancy and implantation rate were similar regardless of the blastocyst quality.
  
  
  CONCLUSIONS
  There was an effect on the clinical outcomes depending on whether the blastocyst hatched during single frozen-thawed blastocyst transfer. When performing single frozen-thawed blastocyst transfer, the hatching status of the frozen-thawed blastocyst may be a more important parameter for clinical outcomes than the quality of the frozen-thawed blastocyst.
authors.affiliation: Maria Fertility Hospital, Seoul, Korea.
authors.forename: Yong Soo
authors.initials: YS
authors.lastname: Hur
authors.affiliation: Maria Fertility Hospital, Seoul, Korea.
authors.forename: Eun Kyung
authors.initials: EK
authors.lastname: Ryu
authors.affiliation: Maria Fertility Hospital, Seoul, Korea.
authors.forename: Seung Hyun
authors.initials: SH
authors.lastname: Song
authors.affiliation: Maria Research Center, Seoul, Korea.
authors.forename: San Hyun
authors.initials: SH
authors.lastname: Yoon
authors.affiliation: Maria Fertility Hospital, Seoul, Korea.
authors.forename: Kyung Sil
authors.initials: KS
authors.lastname: Lim
authors.affiliation: Maria Fertility Hospital, Seoul, Korea.
authors.forename: Won Don
authors.initials: WD
authors.lastname: Lee
authors.affiliation: Maria Fertility Hospital, Seoul, Korea.
authors.forename: Jin Ho
authors.initials: JH
authors.lastname: Lim
keywords: Blastocyst; Single embryo transfer; Vitrification