Comparison of the cryopreservation of human embryos obtained after intracytoplasmic sperm injection with a slow cooling or an ultrarapid cooling procedure

Purpose: Our purpose was to compare an ultrarapid method (URM),modified wit h dimethylsulfoxide (Me2SO) to a slow method (SM) with propanediol (PROH) f or the cryopreservation of extra human embryos in a program of intracytopla smic sperm injection (ICSI). Methods: The extra embryos of 160 patients were cryopreserved in a prospect ive and randomized manner (drawing lots) by a modified URM (3 M Me2SO/0.25 M sucrose/thawing in three sucrose gradients) (Group I) or by a SM (1.5 M P ropanediol/program 0-Cryologic CL863) (Group II). A total of 103 cycles has been thawed thus far The number of thawed cycles was 58 for group I and 45 for group II. Results: The mean age (group I 31.3 +/- 4.5; group II, 31.9 +/- 4.3) did no t differ between the groups (P = 0.38). The number of frozen embryos (group I, 6.6 +/- 3.2; group II, 6.5 +/- 3.2) was similar (P = 0.49) for the two groups, as was the number of thawed embryos (P = 0.52) (group I 6.5 +/- 2.9 ; group 11, 6.2 +/- 3). The survival rate was higher (P < 0.01) for group I I (83.3 +/- 23%) than for group I (69.2 +/- 28.7%). The cleavage rate was a lso higher (P < 0.01) for group 11 (56.8 +/- 31 %) compared with group 1 (2 4.2 +/- 22.4%). The number of embryos transferred did not differ (P = 0.14) between the groups (group I, 3.16 +/- 1.2; group II, 3.5 +/- 1.0). The imp lantation rate (group 1, 6.3%; group II, 13.8%) was significantly significa ntly different between groups (P = 0.034). Pregnancy rates per thawed and t ransferred cycle were higher for group 11 (33.3 and 36.6%, respectively) co mpared with group I (13.8 and 16 %, respectively, and these differences wer e significant (P = 0.03 and P = 0.03, respectively). Conclusion: The data obtained suggest that the SIM is superior to the URM f or the cryopreservation of extra embryos after ICSI.