Purpose: Our purpose was to compare the success rate of transferring frozen-thawed embryos generated from either intracytoplasmic sperm injection (ICSI) or conventional in vitro fertilization (IVF).
Methods: A retrospective review of all frozen-thawed embryo transfer (ET) cycles between January 1995 and April 1997 was performed. There were 83 and 204 transfer cycles of frozen-thawed multicellular embryos generated from conventional IVF (group A) and ICSI (group B), respectively. The survival rate of frozen-thawed embryos and the outcome following ET in both groups were assessed.
Results: The groups did not differ in age (31.7 +/- 4.6 and 30.6 +/- 6.0; mean +/- SD) or number of embryos transferred (3.5 +/- 1.1 and 3.8 +/- 1.3 for groups A and B, respectively). An acceptable pregnancy rate per ET was achieved in both groups, but the rate was significantly higher (P = 0.04) for group A than group B, 32.5 and 20%, respectively. Group A included frozen embryos of a higher quality than those of group B, but the proportion of embryos surviving after thawing was significantly higher for group B than group A (92.5 and 85.6%, respectively; P = 0.0004). The abortion rate did not differ between the two groups: 22 and 26.8% for groups A and B, respectively.
Conclusions: Although an overall high pregnancy rate was achieved following frozen-thawed ET, it was lower for cycles in which embryos had been generated from ICSI. This difference may be attributed to a lower prefreezing embryo quality in the ICSI group. Embryos originating from ICSI were not vulnerable to cryopreservation and, when implanted, resulted in a comparable abortion rate to thawed embryos of conventional IVF.