A modified cryopreservation method increases the survival of human biopsied cleavage stage embryos

The relatively poor survival rate of human biopsied cleavage stage embryos following cryopreservation is a significant obstacle in the application of preimplantation genetic diagnosis (PGD). We have attempted to improve cryosurvival of biopsied embryos by modifying the standard embryo cryopreservation technique.

Biopsied embryos were cryopreserved in 1.5 mol/l 1,2-propanediol in the presence of an elevated concentration of sucrose (0.2 mol/l) and human serum albumin was replaced by maternal serum (20% vol:vol). An additional initial thawing step in the presence of 0.3 mol/l sucrose was also included.

The proportion of biopsied embryos which survived cryopreservation with > or =50% of their blastomeres intact was significantly higher using the modified method (138/185; 75%) than that observed using the standard propanediol method (20/46; 43%; P = 0.022). Total blastomere survival was also significantly increased as a result of the modifications (1010/1513; 67% versus 177/385; 46%; P < 0.001). Six fetal hearts have been detected to date following replacement of biopsied embryos cryopreserved with the modified method.

Survival of human biopsied cleavage stage embryos can be restored to a level similar to that of non-biopsied controls by modification of the cryopreservation procedure. Embryos which have been cryopreserved using the modified method can implant following replacement in utero.