Effect of blastomere loss on the outcome of frozen embryo replacement cycles

To assess the impact of survival of cryopreservation and thawing with all blastomeres intact on the outcome of frozen embryo replacement (FER) cycles.

Prospective observational study.

University-affiliated tertiary referral assisted conception unit.

The number of intact blastomeres before cryopreservation and after thawing was prospectively recorded in 1,687 cleavage-stage embryos thawed in 377 FER cycles. The cycles were categorized into two groups: group A (n = 184) included cycles in which all embryos transferred survived the cryopreservation and thawing process with all their original blastomeres intact; group B (n = 193) included cycles in which embryos transferred included at least one partially damaged embryo that has lost up to 50% of its original blastomere number.

None.

Pregnancy and embryo implantation rates.

Groups A and B were comparable with respect to mean age at cryopreservation, mean number of oocytes retrieved and fertilized normally in the fresh cycle, and mean age at frozen transfer. No significant difference was found between the two groups with regard to mean number of frozen and thawed embryos per cycle and mean endometrial thickness reached before P supplementation. More embryos were transferred per cycle in group B than group A (2.4 +/- 0.6 vs. 2.1 +/- 0.6, respectively). However, the pregnancy and clinical pregnancy rates per cycle were significantly higher in group A than in group B (39.1% and 28.3% vs. 22.8% and 13.5%, respectively). The implantation rate was also higher in group A than in group B (17.3% vs. 8.1%, respectively).

FER cycles in which all embryos transferred remained fully intact at thawing achieve a better outcome than those with at least one partially damaged embryo.