Embryo cryopreservation

Cryopreservation of bovine pre-morula-stage in vitro matured/in vitro fertilized embryos after delipidation and before use in nucleus transfer

We have determined that the tolerance of in vitro matured/in vitro fertilized (IVM/IVF) bovine embryos to cryopreservation at the pre-morula stage can be improved by removal of cytoplasmic lipid droplets by centrifugation. Nucleus transfer was also performed using cryopreserved, delipated (lipid droplets removed) 8- to 16-cell-stage blastomeres of IVM/IVF embryos as donor nuclei. In vitro developmental ability of the delipated embryos to the blastocyst stage (20 of 126) was found to be equal to that of undelipated embryos (35 of 176); and of 53 delipated embryos cryopreserved at the 8- to 16-cell stage, 12 developed into blastocysts in vitro after thawing. On the other hand, only 2 of 43 undelipated embryos and 5 of 59 sham-operated embryos survived (p < 0.05). When blastomeres isolated from cryopreserved, delipated 8- to 16-cell-stage embryos were used for nucleus transfer, 57 of 80 successfully fused with enucleated oocytes, which was significantly lower than the fusion rate obtained with blastomeres of unfrozen, undelipated embryos (93 of 104, p < 0.01). However, the developmental rate to the blastocyst stage for nucleus transfer embryos reconstituted with frozen, delipated blastomeres (9 of 57) was not different from that of the nucleus transfer embryos with unfrozen, undelipated embryos (23 of 93). These results confirm that removal of cytoplasmic lipid droplets from bovine IVM/IVF zygotes allows for successful cryopreservation at the 8- to 16-cell stage and that blastomeres from these embryos can be used as donors of karyoplasts for nucleus transfer.

In vitro maturation and the fertilization and developmental competence of oocytes recovered from untreated polycystic ovarian patients

OBJECTIVE

To determine the maturational and developmental competence of immature oocytes recovered in situ from anovulatory and ovulatory patients with polycystic ovaries (PCO).

DESIGN

A newly designed method for recovery of immature oocytes from 2 to 10 mm follicles by transvaginal ultrasound or laparoscopy was used to compare the recovery and maturation of oocytes from 9 anovulatory polycystic ovarian syndrome (PCOS) patients and 10 ovulatory patients without polycystic ovaries (PCO) (experiment 1). In a second study (experiment 2), we compared the maturation, fertilization, and development of oocytes recovered from another 10 anovulatory PCOS and 13 ovulatory PCO patients. Two types of culture methods and time intervals for maturation were also examined.

RESULTS

In experiment 1, a significantly higher number of immature oocytes were recovered from PCOS patients (15.3) compared with non-PCO patients (2.8). Sixty-five percent of oocytes cultured in medium with gonadotropins, estrogen, and fetal calf serum matured to metaphase II by 43 to 47 hours, and 81% were mature at 48 to 54 hours of culture. Thirty-four percent of the inseminated oocytes fertilized and 56% of the cultured pronuclear oocytes cleaved to eight cells or more. In experiment 2, there was no significant difference between anovulatory PCOS and ovulatory PCO patients in the number of oocytes recovered or their maturation, fertilization, and development. There was no difference between oocytes matured in medium or in coculture with mature granulosa cells, with or without added hCG. However, significantly fewer oocytes were immature and more fertilized when oocytes were inseminated after 34.5 to 35.5 hours of maturation than 29.5 to 32.5 hours of maturation. A pregnancy and the birth of a normal baby occurred in one of the anovulatory PCOS patient receiving an abbreviated steroid replacement protocol after ET.

CONCLUSION

Immature oocyte recovery could be developed as a new method for the treatment of women with infertility due to PCO because the oocytes of these patients retain their maturational and developmental competence.

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

OBJECTIVE

To compare the survival rate of frozen-thawed embryos with perforated zonae from microsurgical fertilization (subzonal insemination) (SUZI) with that of embryos with intact zonae.

DESIGN

Thirty-eight embryos resulting from microsurgical fertilization by SUZI were cryopreserved in 16 patient cycles. Within the same period, 140 zonae-intact embryos from 46 patient cycles were cryopreserved. The survival rate of the SUZI embryos was compared with the zonae-intact embryos after thawing. Clinical pregnancies were compared after the transfer of the thawed embryos.

RESULTS

The total survival rates were 94.7% and 89.3% for thawed SUZI embryos and zonae-intact embryos, respectively. Within each type of embryo, total survival rates were similar irrespective of the age of the embryos at freezing. The blastomere loss per thawed embryo was the same for zonae-intact and SUZI embryos. One clinical pregnancy was obtained in patients who received thawed SUZI embryos and nine in patients who received embryos with intact zonae.

CONCLUSIONS

It is concluded that SUZI embryos can be cryopreserved and thawed with the same degree of confidence as zonae-intact embryos. The low implantation rate of thawed SUZI embryos requires confirmation in a larger clinical series.