title: Human embryo cryopreservation: one-step slow freezing does it all?
abstract: OBJECTIVE
  Previous studies have shown that a modified one-step slow freezing method with higher sucrose concentration (0.2 M) can achieve higher embryo and blastomere survival rates that are comparable to vitrification. However, no study has evaluated the efficacy of a one-step method using commercial slow freezing kit without altering its composition. This retrospective study examines the effects of using 1.5 M PROH with 0.1 M sucrose (F2 medium) alone in a one-step slow freezing method compared to the conventional two-step method.
  
  
  METHODS
  Cleavage stage embryos from 526 thaw cycles previously cryopreserved by either the conventional two-step slow freezing method or the modified one-step method were studied. The embryo and blastomere survival rates, cleavage rate, clinical pregnancy rate and live birth rate were compared between the two groups.
  
  
  RESULTS
  The results showed that the embryo survival rate was significantly higher in the modified one-step method compared to the conventional two-step method (86.9 % and 83.1 %, respectively; p = 0.04). Total blastomere survival rate was also significantly increased as a result of the modification (81.0 % versus 76.5 %; p < 0.001). However, there was no statistical difference in the cleavage rates, clinical pregnancy rates (CPR/ET) and live birth rates between the two methods.
  
  
  CONCLUSIONS
  Slow freezing using the one-step method is superior to the conventional two-step method in terms of embryo and blastomere survival rates without affecting cleavage rate and clinical outcomes. It can be routinely applied to cleavage stage embryo cryopreservation in IVF centres for greater workflow efficiency.
authors.affiliation: KK Women's and Children's Hospital, Department of Reproductive Medicine, KKIVF Centre, Basement 1, Women's Tower KK Women's and Children's Hospital, 100 Bukit Timah Road, Singapore, 229899, Singapore, Chong.Yee.Shen@kkh.com.sg.
authors.forename: Yee Shen
authors.initials: YS
authors.lastname: Chong
authors.forename: Melinda Ling Hou
authors.initials: ML
authors.lastname: Chan
authors.forename: Heng Hao
authors.initials: HH
authors.lastname: Tan
authors.forename: Sadhana
authors.initials: S
authors.lastname: Nadarajah
mesh_terms: D002970:Cleavage Stage, Ovum; D015925:Cryopreservation / Q000379:methods*; D046149:Embryo Culture Techniques; D004624:Embryo Transfer / Q000379:methods; D005260:Female; D005307:Fertilization in Vitro; D005615:Freezing; D006801:Humans; D011247:Pregnancy; D018873:Pregnancy Rate
references.citation: Hum Reprod. 2008 Sep;23(9):1976-82
references.pmid: 18544577
references.citation: Fertil Steril. 1999 Sep;72(3):527-32
references.pmid: 10519629
references.citation: Hum Reprod. 2002 Aug;17(8):2146-51
references.pmid: 12151450
references.citation: Hum Reprod. 1997 Sep;12(9):2006-10
references.pmid: 9363721
references.citation: Toxicol In Vitro. 2001 Dec;15(6):635-42
references.pmid: 11698163
references.citation: J Assist Reprod Genet. 2010 Sep;27(9-10):549-54
references.pmid: 20640501
references.citation: Cryobiology. 2000 Mar;40(2):110-6
references.pmid: 10788310
references.citation: Teratology. 1988 Nov;38(5):467-74
references.pmid: 3238605
references.citation: J Assist Reprod Genet. 2014 Feb;31(2):241-7
references.pmid: 24317854
references.citation: Hum Reprod. 2003 Mar;18(3):568-71
references.pmid: 12615826
references.citation: Reprod Biomed Online. 2006 Jun;12(6):779-96
references.pmid: 16792858
references.citation: Reprod Biomed Online. 2005 Sep;11(3):300-8
references.pmid: 16176668
references.citation: Hum Reprod. 2002 May;17(5):1321-6
references.pmid: 11980759
references.citation: Reprod Biomed Online. 2009 Oct;19(4):521-5
references.pmid: 19909593
references.citation: Hum Reprod. 2000 Jan;15(1):175-9
references.pmid: 10611209
references.citation: Lancet. 1995 Jul 15;346(8968):137-40
references.pmid: 7603227
references.citation: Fertil Steril. 2011 Jun 30;95(8):2628-30
references.pmid: 21704214
references.citation: Hum Reprod. 2001 Mar;16(3):411-6
references.pmid: 11228204
references.citation: Hum Reprod. 2012 Dec;27(12):3609-15
references.pmid: 22990515
references.citation: Fertil Steril. 1995 Dec;64(6):1125-9
references.pmid: 7589664
references.citation: Hum Reprod. 2003 Aug;18(8):1669-73
references.pmid: 12871880
references.citation: Hum Reprod. 2011 Aug;26(8):1987-96
references.pmid: 21586432