Comparative study of the survival rate of frozen-thawed embryos with perforated zonae from microsurgical fertilization and frozen-thawed embryos with intact zonae

Implantation Potential and Clinical Impact of Cryopreservation—A Review

The ability of human embryos to survive the freezing and thawing process is reflected in their implantation potential. Although cryopreservation appears to affect adversely the capacity of human embryos to implant, it has also been shown to enhance consistently IVF outcome. Moreover, despite the reduced implantation potential of cryopreserved embryos as compared to fresh embryos, multiple pregnancies are frequent in frozen embryo transfer (FRET) cycles. There is no conclusive evidence that the stage of development at the time of freezing provides a clear advantage for the outcome of a FRET cycle. On the other hand, a decreased chance for pregnancy achievement appears to exist with advanced maternal age. Neither the mode of endometrium preparation nor the length of cryostorage appears to affect the outcome of FRET cycles which is positively associated to the achievement of pregnancy in the corresponding fresh cycle. Available evidence suggests that there are no adverse consequences in the babies born after embryo cryopreservation, although larger studies are necessary to allow solid conclusions.

A comparison of post-thaw results between cryopreserved embryos derived from intracytoplasmic sperm injection and those from conventional IVF

OBJECTIVE

To study the effect of freezing on early stage embryos derived from intracytoplasmic sperm injection (ICSI) or from IVF.

DESIGN

Prospective, controlled clinical study.

SETTING

Private IVF center.

PATIENT(S)

Sixty-seven consecutive patients undergoing frozen-thawed embryo transfer cycles.

INTERVENTION(S)

Early stage embryos were frozen, thawed, and transferred.

MAIN OUTCOME MEASURE(S)

Post-thaw survival, implantation and pregnancy rates.

RESULT(S)

We noted an 88% post-thaw survival rate, an 18% implantation rate, and a 52% pregnancy rate in the ICSI group and 81%, 11%, and 25%, respectively, with conventional fertilization.

CONCLUSION(S)

Early stage embryos (either zygote or 2-4 cells) derived from ICSI can be frozen with confidence and higher post-thaw survival and pregnancy rates can be achieved when compared with those from conventional IVF.

Reduced survival after human embryo biopsy and subsequent cryopreservation

Preimplantation genetic diagnosis (PGD) is performed in couples at risk of genetic disease, so as to avoid transfer of embryos which are affected by a monogenic disease or which carry chromosomal aberrations. As in all in-vitro fertilization (IVF) cycles, supernumerary non-affected good-quality embryos may be available after PGD. These embryos can be cryopreserved. So far, limited data on survival after cryopreservation of biopsied human embryos are available. In this study, human embryos of good morphological quality derived from abnormal fertilization were used to evaluate the influence of the embryo biopsy procedure on survival after cryopreservation. Embryos were allocated to three different groups: control (n = 20), drilling-only (n = 16), and biopsy (n = 29). After freezing and thawing, a significantly lower number of blastomeres was intact in the drilling-only group (46/118, i.e. 39.0%, P < 0.01) and in the embryo biopsy group (46/156, i.e. 29.5%, P < 0.0001) than in the control group (85/151, i.e. 56.3%). This difference was reflected in survival rates of embryos. Fifty-five per cent of the control embryos, 37.5% of the drilling-only group, and 33.3% of the biopsy group had at least 50% of their blastomeres intact. After further in-vitro culture, four blastocysts, three from the drilling-only group and one from the biopsy group, developed from the surviving embryos. From this study it can be concluded that current cryopreservation procedures are less successful when biopsied human embryos are cryopreserved, but that surviving embryos can develop to the blastocyst stage and thus may have the potential to develop to term.

The outcome of cryopreserved human embryos after intracytoplasmic sperm injection and traditional IVF

OBJECTIVE

Our objective was to analyze the outcome of cryopreserved embryos obtained after intracytoplasmic sperm injection (ICSI) and in vitro fertilization (IVF) in terms of survival rate, implantation rate (IR), total and clinical pregnancy rate (PR) in a retrospective, comparative study.

METHODS

Three hundred seventy-five IVF and 463 ICSI surnumerary cleaved embryos, frozen on Day 2 with 1,2-propanediol, were thawed.

RESULTS

Thirty-two percent of the thawed IVF embryos survived and 11 pregnancies (8 clinical) were obtained from 68 transfers (16.1%). Fourty-seven percent of the ICSI embryos survived, with 19 pregnancies (18 clinical) from 116 transfers (16.4%). The IR was 8.5% (8/94) in IVF cycles and 10.8% (20/185) in ICSI cycles.

CONCLUSIONS

A significantly better survival rate of ICSI embryos was observed but with no difference in PR, preclinical, and clinical abortion rate, or IR.

A comparison of the effects of different degrees of zona pellucida damage followed by cryopreservation on the postthaw development of mouse embryos

PURPOSE

The totally intact zona pellucida is not essential for the development of embryos. It is still unclear how much effect the degree of damages to the zona pellucida will have on the developmental potential of postthaw embryos after cryopreservation. We compared the developmental potential of cryopreserved mouse embryos after induction of two degrees of mechanical damage to the zonae pellucidae by micromanipulation.

METHODS

In experiment I, the development of 124 cryopreserved ICR mouse embryos to the blastocyst stage after zona pellucida penetration of two-cell embryos as in the procedures of subzonal sperm insertion (SUZI) was compared with the development of zona-intact cryopreserved embryos. In experiment II, the zonae pellucidae of 93 two-cell mouse embryos were dissected as in the procedures of partial zonal dissection (PZD), following which the embryos were frozen. This postthaw development was also compared with that of zona-intact two-cell cryopreserved embryos. All the embryos were thawed and cultured to the blastocyst stage. Additional controls were provided by culturing zona-intact and zona-penetrated or zona-dissected embryos without cryopreservation.

RESULTS

The development of unfrozen mouse embryos was not affected by either zona penetration (P = 0.433) or zona dissection (P = 0.659). The developmental potential of cryopreserved mouse embryos was significantly affected after zona dissection (blastocyst rate, 31% ZD vs 72%, control; P < 0.001) but not after zona penetration (blastocyst rate, 59% ZP vs 64% control; P = 0.441).

CONCLUSIONS

The quality of cryopreserved embryos was affected by a large hole on the zona pellucida created by zona dissection but not by simple zona penetration.