Embryo freezing

Survival rates of young cancer patients have shown a positive trend in recent decades, particularly in case of breast cancer and Hodgkin’s disease. Advances in treatment modalities have raised awareness of the need for effective and safe fertility preservation procedures for young women with malignancies. The Ethics Committee of the American Society for Reproductive Medicine (ASRM) and the American Society of Clinical Oncology (ASCO) recommend that physicians advise cancer patients of their fertlity-preserving options before cancer treatment is initiated and inform them that sperm and embryo freezing are the only established methods of fertility preservation. Other fertility preservation methods should be considered investigational and should only be performed in centers with the necessary expertise.

The most successful approach is embryo cryopreservation, as this technique yields a pregnancy rate of 20-30 % if at least two embryos are available for replacement. However, there are some drawbacks:

1) The patient must have a male partner or use donor sperm.

2) Ovarian stimulation, oocyte retrieval and IVF cause a delay in the initiation of chemotherapy or radiotherapy, which may not be acceptable in some cases.

3) High estrogen concentrations associated with ovarian stimulation may be contraindicated in women with estrogen-sensitive malignancies.

Different factors influence the success rate after frozen-thawed embryo replacement. Some are clinical (patient profile, hormone replacement therapy and transfer technique), while others are biological (embryo quality, methods of freezing and thawing). In our department, between 1987 and 2004, we thawed 20 318 embryos, obtaining an overall survival rate of 66% and a pregnancy rate per replacement of 22.5%. Five parameters were positively related to implantation:

1. Four or more cells at the time of freezing (day 2)
2. Resumption of mitosis after thawing
3. More than six cells at transfer (day 3)
4. Assisted hatching
5. Child from a previous fresh cycle

For young cancer patients, it is important to know the impact of the duration of freezing on survival and pregnancy rates. We analyzed pregnancy rates obtained with frozen-thawed embryos 7 years, 7-9 years and more than 9 years after cryopreservation and did not observe any difference between the three groups, with a child born after 10 years and another after 14 years of freezing (Table 1). We reported the birth of a healthy boy 4 years after embryo cryopreservation in a patient with a bilateral borderline ovarian tumor.

At present, it appears that:

1. Embryo freezing is the most efficient technique for fertility preservation.
2. Freezing of early-stage embryos (PN and cells) yields better survival and pregnancy rates than blastocyst freezing and thawing.
3. The duration of freezing does not affect embryo survival after thawing or implantation potential.
4. Vitrification will probably serve to improve embryo cryopreservation results in the near future.

Embryo freezing

Institut Universitari Dexeus embryo freezing results according to the duration of freezing (years)

n = 2547 frozen-thawed embryo replacements

n.s.