Evaluation of blastocyst recuperation, implantation and pregnancy rates after vitrification/warming or slow freezing/thawing cycles

Cryopreservation of human embryos by vitrification or slow freezing: which one is better?

“…When the two studies that transferred embryos at the cleavage stage were combined [3,12 ], no significant difference in clinical pregnancy rates per transfer between vitrification and slow freezing was detected (OR: 1.82, 95% CI: 0.88-3.74, fixed effects model). Similarly, in the study by Bernal et al [7], no difference in clinical pregnancy rates per transfer was observed by transferring blastocysts cryopreserved using vitrification versus slow freezing (64.5 versus 54.9%, respectively; rate difference: þ9.6%, 95% CI: À8.2 to þ26.9).…”

“…in the setting of an IVF program, it is necessary to define the outcome measures that will be used for this purpose. Several outcome measures have been proposed so far in the literature including postthawing survival rate, cleavage rate, blastulation rate and hatching rate [3][4][5][6][7]. Although the above outcome measures are useful in describing the efficacy of the cryopreservation method per se, assessment of the probability of pregnancy remains the key issue for the clinician.…”

“…The study by Bernal et al [7] evaluated the comparative efficacy of the two cryopreservation methods by randomizing 51 and 64 patients to slow freezing and vitrification, respectively. Cryopreservation of all embryos was performed at the blastocyst stage.…”

“…Regarding clinical pregnancy rates, only three RCTs provided relevant data [3,7,13]. When the two studies that transferred embryos at the cleavage stage were combined [3,12 ], no significant difference in clinical pregnancy rates per transfer between vitrification and slow freezing was detected (OR: 1.82, 95% CI: 0.88-3.74, fixed effects model).…”

“…By pooling the results from these three studies, no significant difference in clinical pregnancy rates per transfer could be detected between the two cryopreservation methods (OR: 1.66, 95% CI: 0.98-2.79, fixed effects model) [3,7,13]. Live birth was reported only in the study by Rama Raju et al [3], and it was also not significantly different between vitrification and slow freezing (32.5 versus 13.0%, respectively; rate difference: þ19.5%, 95% CI: À3.3 to þ37.1).…”