Posted on December 7th, 2020by Dr. Taraneh Nazemin Fertility Preservation

To Freeze or Not to Freeze: That’s Not the Only Question

Exploring the differences between egg and embryo freezing

Fertility preservation has been an evolving area in the field of reproductive medicine. There are multiple ways to preserve one’s fertility, but the two most common methods are through egg freezing, also known as “oocyte cryopreservation,” and embryo banking, in which an egg is fertilized prior to undergoing the freezing process. There are benefits to both methods of fertility preservation and ultimately the question boils down to: what is the right fit for you?

The process of egg freezing or embryo banking is nearly identical. In order to make eggs or embryos, one must undergo the IVF process. This involves about 9-12 days of hormonal injections to stimulate the ovaries to grow and mature multiple eggs. Patients then undergo an egg retrieval in which all their stimulated eggs are removed and evaluated in the laboratory.

The difference between egg and embryo freezing begins after the egg retrieval, at which point either a mature oocyte is frozen through the process of “vitrification,” or inseminated with sperm in order to fertilize and make embryos. Embryos are then typically left in culture until day 5, 6, or 7, during which time they develop into a blastocyst, or an expanded embryo comprising of about 100-200 cells. At this stage of embryonic development it is possible to take a sample of approximately 3-5 cells for pre-implantation genetic testing for aneuploidy (PGT-A) to determine the chromosomal copy number of the embryo (e.g. 46 XY, 46 XX or an abnormal complement of chromosomes.) Embryos are then frozen by vitrification and preserved.

The shared advantage of egg or embryo freezing is the ability to “stop the biological clock.” Since women are born with all the eggs they will have throughout their lifetime and both the quantity and the quality of eggs deteriorates over time, egg/embryo banking is a method that stops this aging process. But while fertility preservation may “stop the clock,” it cannot change the quality of the eggs frozen. Oocyte cryopreservation is limited by the inability to test the quality of the eggs prior to freezing them. And since not every egg will result in the birth of a child, it’s important to consult with a reproductive specialist to determine a reasonable goal for fertility preservation treatment.

Embryo banking, and the use of PGT-A, conversely offers the added benefit of having qualitative information about what is being stored. But embryo banking is not something to consider lightly. Embryos are shared property of the two individuals who created them, and decisions about their use must be mutually determined. Egg freezing has the advantage of so-called “reproductive independence,” and allows for a woman to preserve her fertility without a male partner.

When the time comes to use frozen eggs or embryos, outcomes are comparable. While frozen eggs are deemed a little more fragile, oocytes and embryos have similarly high rates of successful thawing (80-90% vs 95-98%) and fertilization (70% vs. 80%). After oocytes are thawed, fertilized and placed in extended culture, there is also the option to pursue PGT-A testing if desired. Ultimately, the main determinant of success with both egg and embryo banking is the age at which they were frozen.

Fertility preservation has opened up new opportunities for women and couples to “stop the biologic clock” and delay childbearing for a multitude of reasons. Egg and embryo banking have different advantages with similarly high rates of success. Meeting with a reproductive specialist can help in determining which method of fertility preservation is right for you and it is the first step in taking control of your reproductive journey.

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