Embryo freezing, or cryopreservation, adds an important dimension to assisted reproduction by:
We define embryo survival based on the number of viable cells in an embryo after thawing. An embryo has “survived” if >50% of the cells are viable. We consider an embryo to “partially survive” if < 50% of its cells are viable, and to be “atretic” if all the cells are dead at thaw. Approximately, 65-70% of embryos survive thaw, 10% partially survive, and 20-25% are atretic. Our data suggests that embryos with 100% cell survival are almost as good as embryos never frozen, but only about 30-35% survive in this fashion.
Embryo morphology (appearance of the cells / percentage of fragmentation) is one of the most influential factors for embryo survival. Interestingly, embryos produced from intracytoplasmic sperm injection (ICSI) also seem to survive somewhat better than embryos produced from conventional insemination. The following graph illustrates these points. The embryo grade in the graph goes from worst (3.2) to best (1.0).
Embryos that are 2, 4, or 8 cells when frozen have about 5-10% greater survival than embryos with an odd number of cells. Donor egg embryos have a 2-5% greater survival rate than embryos from infertile women when compared by morphology score.
Pregnancy rates are similarly affected by complex relationships and like embryo survival only 7-10% of the predictive value can be observed and measured. Age is not a significant factor with frozen embryos but fewer older women have frozen embryos. From the approximately 20 factors reviewed, the most important factors predicting pregnancy rates are the number of surviving embryos transferred, the number of 100% surviving embryos transferred, and the morphology scores of the transferred embryos. The delivered pregnancy rates ranged from 5% (a single poor quality embryo) to 36% (4 high quality embryos) when the cycles from 1987 to 2001 were combined.
Blastocysts (embryos cultured for 5 days rather than 2-3) are a special case. The embryos are much larger and have special needs with regard to freezing without damage. Many centers have had trouble with blastocyst cryo-survival and pregnancy rates. A new protocol developed in our laboratory and implemented in December 2000 led to a transfer rate of 62% and a 35% pregnancy rate per transfer. This important change now makes blastocyst transfer more appealing since excess blastocysts can be expected to yield pregnancy rates comparable to embryos frozen two to three days after retrieval.
Embryos are frozen with an IVF /ICSI cycle. So, the cost of IVF / ICSI would apply. There would be an additional cost of freezing th embryos and storing them per year. For details on costs, email us on email@example.com