Cryopreservation is a crucial technique in fertility preservation, offering hope to individuals and couples wishing to conceive in the future. This process can be particularly significant for cancer patients, who may face fertility-compromising treatments.
The American Society for Reproductive Medicine (ASRM) outlines two primary methods of cryopreservation: embryo cryopreservation and egg (oocyte) cryopreservation, each with its own procedures and considerations. Let's discuss what each procedure is, how it works, and their respective success rates.
How Embryo Cryopreservation vs. Egg Cryopreservation Works for IVF
Embryo Cryopreservation
Embryo cryopreservation is the process of freezing embryos after in vitro fertilization (IVF) to preserve future fertility. The IVF procedure involves stimulating the ovaries with hormones to produce multiple eggs, which are then retrieved and fertilized with sperm in a laboratory setting. The resulting embryos can undergo preimplantation genetic diagnosis (PGD) for specific genetic conditions before being frozen for future use. This method requires the availability of sperm, either from a partner or a donor. It's noted that the hormonal stimulation involved in egg production might increase estrogen levels, potentially exacerbating certain cancers, posing a risk for some patients.
Egg Cryopreservation
Egg cryopreservation might be preferred by those without a male partner or due to personal or religious reasons. This technique has seen significant improvements over the past decade, making it a viable option for many. Like embryo cryopreservation, it involves hormonal stimulation and IVF but differs in that the eggs are frozen unfertilized. After cancer treatment, the eggs can be thawed, fertilized, and implanted. This method provides flexibility for those unsure about immediate fertilization or without immediate access to sperm.
Embryo vs. Egg Cryopreservation for IVF Success Rates
The success rates of pregnancy vary between embryo and egg cryopreservation.
Embryo cryopreservation generally offers higher pregnancy rates because the embryos have already demonstrated their viability by surviving the initial stages of development. The process of freezing and thawing embryos tends to have a higher success rate of implantation compared to eggs.
Egg cryopreservation, while having improved significantly, still typically results in lower pregnancy rates per frozen egg compared to per frozen embryo. This discrepancy is attributed to the fact that not all thawed eggs will survive the fertilization process or develop into viable embryos.
ASRM has also shared that more data is required for egg cryopreservation, given it was only in 2013 that they declared it no longer "experimental." Since many women have proactively frozen their eggs for future use, more data is required. Nonetheless, the difference is an important consideration.
In summary, embryo cryopreservation is often seen as offering the best chance for future pregnancy, particularly for those who have a partner or are open to using donor sperm at the time of freezing. Egg cryopreservation, however, provides an important option for those seeking to preserve fertility without immediate fertilization, offering flexibility for future family planning.
Both methods involve complex considerations, including the potential impact on hormone-sensitive cancers, and require personalized consultation with fertility and oncology specialists.