In the past, women only had the option of freezing an embryo if they wanted to preserve their fertility. This meant that if the woman was single and wanted to preserve her fertility, she had to find a sperm donor to fertilize the egg before it was frozen.
However, after the ASRM (American Society for Reproductive Medicine) lifted the experimental label for oocyte cryopreservation (egg freezing) in 2012, women today can either freeze their eggs or embroyos for fertility preservation. So which is a better option for you?
Understanding the Fertility Preservation Process
The beginning process of egg freezing and embryo freezing is the same. First, the woman receives hormone medications to stimulate the ovaries to produce multiple mature eggs. The fertility doctor will monitor the maturation of the eggs during this time to determine the timing of the retrieval. Once the eggs are matured, the patient will undergo a minor surgical procedure to retrieve the matured eggs.
After the retrieval of the matured eggs, the process for egg freezing and embryo freezing diverges. In egg freezing, the collected eggs are processed and frozen soon after the retrieval. In embryo freezing, an additional step of fertilizing the egg with sperm is needed before it is frozen. The collected eggs are processed, fertilized with sperm, developed into an embryo before freezing.
The embryos and eggs are typically frozen by a process called vitrification. The frozen eggs or embryos will be stored at deep sub-zero temperatures (-196 degrees Celcius) in liquid nitrogen until they are ready to be thawed for future fertility procedures.
The Differences: Frozen Embryos vs Frozen Eggs
For just freezing embroyos
Frozen embroyos are more stable and less prone to damage during the freezing and thawing processes compared to frozen eggs. Also, for retrieved embryos you can test for chromosomal abnormalities, which can increase the odds for live births, but you cannot test retrieved eggs. Therfore, using frozen embryos can potentially provide a better pregnancy outcome later in life than using frozen eggs.
For IVF cycling
There are also many other benefits of freezing embryos. In a standard IVF cycling, freezing embryos can minimize the risk of multiple pregnancy by reducing the number of embryos transferred during a fresh cycle, avoid repeating stimulation cycles, and increasing cumulative pregnancy rates. Some studies showed that women who had transfers of fresh and frozen embryos obtained an 8% additional births by using their frozen embryos. Additionally, with the success rates of post thaw embryo transfer nearing those of fresh embryo transfer couple, the use of frozen embryos is now a routine procedure in assisted reproduction technology. Thus, the number of live births in woman undergoing IVF with post thaw embryo doubled from 12% in 1997 to 25% in 2011.
Diversity: More patient populations
Egg freezing can offer more options for diverse patients populations in fertility preservation compared to embryo freezing. These include single women who will undergo fertility compromising cancer treatments, women looking to postpone childbirth to pursue educational or career goals, and those who have diminished ovarian reserve and haven’t met their significant other.
Improved technology: Comparable to retrieved fresh eggs
The technology for egg freezing has improved with vitrification and studies have shown signficant improvements in the post thaw survival rates and clinical pregnancy rates compared to the traditional slow freezing method. Freezing with vitrification has been shown in several studies to have high post thaw survival ranging from 79% to 99%. In 2011, Cobo and Diaz conducted a systematic review comparing vitrified and fresh eggs that showed similar fertilization rates and clinical pregnancy rates between the two groups.
Controversies of Embryo and Egg Freezing
The storage of frozen embryos has generated ethical, legal, and religious concerns in some countries due to the concerns on the fate of the surplus frozen embroyos in storagge. Due to this controversy, countries like Italy and the United Arab Emirates have enacted specific laws that prohibit embryo freezing.
Egg freezing is controversial in some countries with conservative family values, therefore its use is strictly controlled. In China, egg freezing is prohibited to single women whereas in Singapore, only women with certain medical needs such as fertility preservation for cancer patients undergoing chemotherapy are allowed.
Safety of egg and embryo freezing
Recent data shows no increase in the number of congenital abnormalities observed in thawed eggs or embryos. Although freezing eggs and embryos are now well-established procedures, caution is advised until there are sufficient data to rule out potential long-term side effects for these children.
Which is better?
Egg and embryo freezing are now an established technology with high success rates and used for a wide range of indications. It just comes down to lifestyle and circumstances. Women who do not have partner or do not wish to store embryos due to ethical and morals considerations are good candidates for egg freezing. While for couples who want to achieve children later, embryos freezing could be a better option than freezing eggs or sperm separately.
Wong KM, Mastenbroek S, Repping S. Cryopreservation of human embryos and its contribution to in vitro fertilization success rates. Fertil Steril. 2014;102(1):19-26.
János Konc, Katalin Kanyó, Rita Kriston, Bence Somoskői, Sándor Cseh. Cryopreservation of Embryos and Oocytes in Human Assisted Reproduction. BioMed Research International. 2014. doi:10.1155/2014/307268
Cobo A, Diaz C. Clinical application of oocyte vitrification: a systematic review and meta-analysis of randomized controlled trials. Fertil Steril. 2011;96(2):277-85.