Cryopreservation at a glance
- Cryopreservation is the freezing and storing of mature eggs (oocytes), fertilized eggs (embryos) or sperm for later use in fertility treatments.
- Cryopreservation assists couples or women who plan to have children in the future and wish to save existing healthy eggs or sperm before age diminishes their quality and chance of successful pregnancy.
- Men and women facing cancer treatments or other medical conditions that can render them infertile can use cryopreservation.
- Some patients already undergoing in vitro fertilization (IVF) use cryopreservation to preserve extra embryos for use in later IVF treatments.
What is cryopreservation?
Cryopreservation is the freezing of mature eggs, sperm or embryos for later use in assisted reproductive treatments. Freezing stops all biologic activity and preserves existing cells’ viability.
Ongoing advances in cryopreservation improve the process and success rates, resulting in an increase in its use. In 2012, the American Society for Reproductive Medicine determined that egg freezing should be included in standard clinical practice, and should no longer considered experimental.
The preferred method of freezing is called vitrification, a flash-freezing method where the cells are first bathed in cryoprotectant and rapidly cooled to -320 degrees F by direct exposure to liquid nitrogen. Vitrification results in the lowest occurrence of ice crystal formation, which can damage cells by causing them to tear or rupture.
The process of freezing suspends all biological activity until the cells are thawed for use in the future. Frozen eggs, embryos or sperm are typically stored in a fertility clinic or cryopreservation bank. There isn’t sufficient data to indicate how long frozen embryos, eggs and sperm remain viable, but most researchers believe long-term freezing (10 years and more) does not diminish quality.
Egg freezing (oocyte cryopreservation)
Oocyte cryopreservation is the freezing and storage of unfertilized eggs (oocytes). The woman takes hormone injections in order to stimulate egg production and an ovulation inducing medication once the eggs are mature. The eggs are then extracted via a simple outpatient surgical procedure and frozen.
When the woman or couple is ready to begin fertility treatment, the frozen eggs are thawed and used during IVF. Because freezing tends to harden the egg’s shell, making it difficult for the sperm to penetrate it, intracytoplasmic sperm injection (ICSI), is performed when frozen eggs are used. ICSI involves the injection of one sperm directly into the egg.
Egg freezing is an option that can make it possible for a woman to become pregnant using her own healthy eggs in the future. This may be beneficial for women whose careers are hazardous or demanding, or who prefer to delay motherhood for relationship reasons. It can also be beneficial for women who will undergo cancer treatment that could be detrimental to her fertility.
Embryo cryopreservation is the preservation of fertilized eggs by freezing. This method is generally used when more viable embryos are produced than are used in an IVF treatment cycle. The woman may choose to transfer a single fresh embryo into her uterus and freeze the others, preserving them for later use.
After retrieval and fertilization of eggs using IVF, embryos are then allowed to mature from 3-5 days and are then frozen. The embryos are stored and later warmed for IVF transfer.
Ovarian tissue cryopreservation
Ovarian tissue cryopreservation can be used for women who must immediately receive aggressive chemotherapy or radiation treatment for cancer that can make her infertile. The immediacy of the treatment precludes egg or embryo freezing, which can take 4-6 weeks.
Considered an experimental treatment by ASRM, ovarian tissue cryopreservation may be the only option available to preserve future ability for pregnancy in prepubertal girls needing such immediatecancer treatments. It may also be used for women with sensitivities to the hormones used in egg retrieval.
Sperm cryopreservation is the freezing and storage of sperm for future use. Because sperm has a lower water content (about 50 percent) than a woman’s egg, it tends to be less susceptible to damage from ice crystal formation during the vitrification process.
Men may opt to preserve their sperm for the future if they have careers that are dangerous or demanding, or if they will have cancer treatment or some other medical condition that can damage their fertility.
How long frozen sperm remains viable isn’t known, but 20-year-old and older frozen sperm have resulted in successful pregnancies. Male fertility declines somewhat with age, though not as markedly as does female fertility, so some men freeze sperm to use in conception efforts later in life.
Why use cryopreservation?
Cryopreservation is a fertility preservation option for couples or individuals who:
- Wish to have children in the future but who are not currently ready due to career, relationship or other factors.
- Will be undergoing treatment for cancer or other serious diseases that could affect their fertility.
- Have extra viable embryos remaining after a cycle of IVF that they hope to use to attempt another pregnancy in the future.
Risks of cryopreservation
The high water content of unfertilized eggs can lead to a higher instance of ice crystal formation, as compared to frozen embryos or sperm. However, recent improvements have increased the safety and success of the cryopreservation process, particularly for unfertilized eggs. Studies show that there is no increase in the risk of birth defects among children born via cryopreservation compared with normal births.
Ethical and moral issues related to cryopreservation generally involve concern over destroying unused frozen embryos or eggs. Fertility physicians can refer patients with such concerns to specialized fertility counselors. Couples may also choose to only freeze eggs or embryos that will be implanted in the mother’s uterus.
Benefits of cryopreservation
Cryopreservation can benefit those who must undergo treatments for cancer or other serious diseases that can be damaging to reproductive capability, or for men or women who wish to delay pregnancy until later in life.
Cryopreservation adds minimal extra risk for those already using the IVF process and can help save the patients’ time and money in the case of freezing extra embryos for use in later IVF cycles.