Fertility preservation offers individuals and couples options to maintain their reproductive choices. Deciding whether to freeze eggs or embryos is a personal consideration. Both methods offer pathways to future parenthood, but involve distinct processes and outcomes. This article explores the procedures, success rates, and personal factors influencing this decision.
Egg Freezing Process
The process of egg freezing begins with ovarian stimulation. This phase involves daily self-administered hormone injections, typically lasting 10 to 12 days, to encourage the ovaries to produce multiple mature eggs instead of the single egg released in a natural cycle. Regular monitoring through blood tests and ultrasounds tracks hormone levels and the growth of ovarian follicles.
Once follicles are adequately sized, a “trigger shot” is administered, preparing the eggs for retrieval. About 36 hours later, the eggs are retrieved during an outpatient procedure performed under sedation. A physician uses a transvaginal ultrasound to guide a thin needle into the ovaries, aspirating fluid from the follicles to collect the mature eggs.
After retrieval, mature eggs are prepared for freezing using a rapid method called vitrification. This technique involves exposing the eggs to cryoprotectants, which remove water from the cells, and then flash-freezing them in liquid nitrogen to -196°C. Vitrification prevents the formation of damaging ice crystals, preserving the egg’s structure until ready for future use.
Embryo Freezing Process
Embryo freezing shares initial steps with egg freezing, including ovarian stimulation and egg retrieval. The key difference is that retrieved eggs are fertilized before freezing. This occurs through in vitro fertilization (IVF), combining sperm with eggs in a laboratory.
Fertilization can occur through conventional insemination (sperm placed with eggs) or intracytoplasmic sperm injection (ICSI), where a single sperm is injected into each mature egg. After fertilization, embryos are cultured for several days. They are typically frozen at either the cleavage stage (day three) or blastocyst stage (day five or six).
Vitrification, the same rapid freezing method used for eggs, is also the primary method for freezing embryos.
Success Rates and Viability
Success rates for frozen eggs and embryos depend on several factors. Embryos generally show higher survival and live birth rates after thawing compared to eggs. This is partly because embryos have already demonstrated their ability to fertilize and develop, suggesting viability.
Age at the time of freezing is a primary determinant of success for both methods. Younger individuals yield higher quality eggs and embryos, leading to better outcomes. For instance, a 30-year-old might have a higher chance of success with fewer frozen eggs than a 40-year-old, who may need to freeze more eggs for similar live birth probabilities.
The number of eggs or embryos frozen also influences overall success. A larger number increases the likelihood of viable material for future attempts. While vitrified egg survival rates are high, not all thawed eggs fertilize, and not all fertilized eggs develop into viable embryos. Embryos, having passed fertilization and early development, often have a more predictable path to implantation and live birth.
Key Factors for Decision Making
Beyond clinical success rates, personal and practical factors influence the choice between freezing eggs and embryos. Relationship status is a key consideration; single individuals typically opt for egg freezing, while partnered individuals may choose embryo freezing if a sperm source is available. This aligns with current life circumstances and family planning goals.
Ethical and religious beliefs also play a role, particularly concerning embryo creation and storage. Some individuals or couples have reservations about creating multiple embryos and storing or discarding unused ones. Egg freezing avoids these specific ethical dilemmas, as unfertilized eggs do not carry the same moral status as embryos for all.
Financial implications are another practical consideration, as procedure and long-term storage costs vary. While initial retrieval costs might be comparable, embryo freezing typically involves additional expenses for fertilization and genetic testing. Emotional aspects, including the psychological comfort of preserving fertility versus embryo creation complexities, also factor into this personal decision.