Impairment of the developmental potential of frozen-thawed human zygotes obtained after intracytoplasmic sperm injection.

Objective: To evaluate the effects of cryopreservation on the survival, cleavage, and morphology of embryos and on the implantation and embryonic loss rates of human zygotes obtained after ICSI compared with frozen-thawed zygotes obtained after traditional IVF. A further objective was to evaluate the same parameters in nonfrozen sibling ICSI and IVF zygotes and to compare them with corresponding frozen-thawed zygotes.

Design: Open, retrospective, comparative study.

Setting: University-associated assisted reproductive program.

Patient(s): Couples with severe male factor infertility and couples undergoing IVF during the same period.

Intervention(s): A cohort of 408 ICSI zygotes and 299 IVF zygotes was frozen in 1,2 propanediol and sucrose using a slow-freezing protocol. Both groups of zygotes were frozen at approximately the same time after microassisted or conventional insemination. One hundred and eighty-seven ICSI and 110 IVF frozen zygotes were rapidly thawed during 44 ICSI cycles and 24 IVF cycles. Zygotes that appeared to have survived were cultured for 24 hours, and most of these embryos that were morphologically normal were transferred into patients.

Main Outcome Measure(s): Survival rate (morphologically intact after thawing), cleavage rate and morphology of embryos, implantation rate, and the incidence of embryonic losses.

Result(s): Except for survival rates, for which both ICSI and IVF frozen-thawed zygotes showed similar and relatively high values (87.7% and 89.1%), the outcomes of other parameters evaluated were significantly different. Thus, from a total of 128 ICSI and 68 IVF embryos transferred, 14 (10.9%) and 17 (25.0%) implanted in 44 ICSI and 24 IVF frozen-thawed cycles, respectively. This difference in implantation corresponded with the rate of cleavage and morphology of the replaced embryos; the embryos that developed from frozen-thawed IVF zygotes cleaved faster and were more regular compared to the frozen-thawed ICSI zygotes. The embryonic loss rate was 57.1% for cryopreserved ICSI zygotes and 11.8% for IVF zygotes. On the other hand, no difference in cleavage pattern, embryo morphology, implantation, and embryonic loss rates was found between nonfrozen sibling ICSI and IVF zygotes.

Conclusion(s): The zygotes arising from ICSI cycles survived cryopreservation at a rate similar to IVF zygotes, but their ability to implant and develop further was probably affected by the cryopreservation procedure. The timing of zygote freezing was considered to be the principal reason for the lower developmental potential of frozen-thawed ICSI zygotes in the present study.