Over the years since the world’s first baby was born from IVF in 1978, fertility clinics have become highly proficient in freezing and storing embryos. But while embryo freezing is a common process, the freezing and thawing of eggs is far more difficult.
The good news is that quickly advancing medical technologies are bringing increased hope to women hoping to preserve their fertility for either health reasons or personal circumstances.
Known clinically as “human oocyte cryopreservation,” the egg freezing process includes extracting, freezing and storing a woman’s eggs (oocytes); then, months or years later, ideally the eggs can be thawed, fertilized, and transferred to the uterus as embryos.
The History of Egg Cryopreservation
Cryopreservation is certainly not new in the field of reproductive medicine. Clinics and tissue banks have been freezing sperm since the 1950s and embryos since the 1980s. A short time later, cryoprerserved oocytes proved successful in 1984, when doctors in Australia claimed the world’s first pregnancy using frozen eggs.
But while sperm and embryo freezing have become routine, the success of egg cryopreservation has developed at a slower pace. This is largely because eggs are one of the largest cells in the body, and cells consequently risk damage in the freeze-thaw process.
For this reason, pregnancy rates from oocyte cryopreservation have traditionally been much lower than in traditional in vitro fertilization (IVF) using either fresh or frozen embryos. But advances in freezing processes, especially vitrification, have resulted in pregnancy rates from frozen approaching rates for cryopreserved embryos.
Recent Advances Mean New Hope
As egg freezing outcomes improve, three groups may soon be able to benefit from oocyte cryopreservation:
- Women who have been diagnosed with cancer but have not begun chemotherapy or radiotherapy.
- Women who wish to use assisted reproductive technologies but do not want to consider embryo freezing for religious and/or moral reasons.
- Women wanting to preserve their future fertility, either because they do not yet have a partner, or for other personal or medical reasons.
Because cancer treatments are often highly damaging to oocytes, egg freezing offers women diagnosed with cancer the chance to preserve their eggs so that they might be able to have children in the future.
For other women, there are different advantages. Some healthy women undergoing IVF object to the practice of freezing excess embryos. Oocyte cryopreservation allows them to fertilize only the minimum number of eggs needed for a single treatment cycle, freezing additional eggs for later use. This way, they do not have to face the question of what to do with excess embryos.
Still other women are choosing egg freezing in order to focus on different pursuits – such as education, career or travel – with plans to attempt childbearing later. Freezing healthy eggs at an early age may optimize chances for a future pregnancy.
Finally, young women with a family history of premature menopause can freeze their eggs in case their eggs are depleted at an early age.
The egg freezing process
Egg retrieval for oocyte cryopreservation is similar to that for in vitro fertilization (IVF). After an evaluation of overall and reproductive health, the woman takes ovulation-inducing medication.
The goal is to stimulate the ovaries in order to produce a sufficient amount of eggs in one cycle (or treatment) for retrieval. The retrieval procedure is a minor outpatient surgical process conducted in a clinic with mild sedation.
Although the largest single cell in the human body, the human egg is also exceptionally fragile. In current circumstances, some will undoubtedly be lost in the freezing and thawing processes. However, much research is underway into new ways to bring more eggs successfully through the cryopreservation process.
When the woman is ready to attempt conception, an embryologist thaws her eggs and fertilizes those that survive the thaw by injecting each egg with a sperm. A physician then transfers the embryos into her uterus.
The Future of Oocyte Cryopreservation
All over the world physicians and scientists have documented hundreds of births from oocyte cryopreservation, and rates of birth defects and chromosomal defects appear to be about the same as that of the general population. The total cost to utilize egg freezing to achieve a pregnancy is comparable to that of IVF. There is also a separate egg storage fee.
