Egg freezing, also known as mature oocyte cryopreservation, is a method used to save women's ability to get pregnant in the future.

Eggs harvested from your ovaries are frozen unfertilized and stored for later use. A frozen egg can be thawed, combined with sperm in a lab and implanted in your uterus (in vitro fertilization).

Your doctor can help you understand how egg freezing works, the potential risks and whether this method of fertility preservation is right for you based on your needs and reproductive history.

Egg freezing might be an option if you're not ready to become pregnant now but want to try to make sure you can get pregnant later.

Unlike with fertilized egg freezing (embryo cryopreservation), egg freezing doesn't require sperm because the eggs aren't fertilized before they're frozen. Just as with embryo freezing, however, you'll need to use fertility drugs to make you ovulate so that you'll produce multiple eggs for retrieval.

You might consider egg freezing if:

• You have a condition or circumstance that can affect your fertility. These might include sickle cell anemia, autoimmune diseases such as lupus, and gender diversity, such as being transgender.
• You need treatment for cancer or another illness that can affect your ability to get pregnant. Certain medical treatments — such as radiation or chemotherapy — can harm your fertility. Egg freezing before treatment might enable you to have biological children later.
• You're undergoing in vitro fertilization. When undergoing in vitro fertilization, some people prefer egg freezing to embryo freezing for religious or ethical reasons.
• You wish to preserve younger eggs now for future use. Freezing eggs at a younger age might help you get pregnant when you're ready.

You can use your frozen eggs to try to conceive a child with sperm from a partner or a sperm donor. A donor can be known or anonymous. The embryo can also be implanted in the uterus of another person to carry the pregnancy (gestational carrier).

Egg freezing carries various risks, including:

• Conditions related to the use of fertility drugs. Rarely, use of injectable fertility drugs, such as synthetic follicle-stimulating hormone or luteinizing hormone to induce ovulation, can cause your ovaries to become swollen and painful soon after ovulation or egg retrieval (ovarian hyperstimulation syndrome). Signs and symptoms include abdominal pain, bloating, nausea, vomiting and diarrhea. Even rarer is the possibility of developing a more severe form of the syndrome that can be life-threatening.
• Egg retrieval procedure complications. Rarely, use of an aspirating needle to retrieve eggs causes bleeding, infection or damage to the bowel, bladder or a blood vessel.
• Emotional risks. Egg freezing can provide hope for a future pregnancy, but there's no guarantee of success.

If you use your frozen eggs to have a child, the risk of miscarriage will be primarily based on your age at the time your eggs were frozen. Older women have higher miscarriage rates, mainly due to having older eggs.

Research to date hasn't shown an increase in the risk of birth defects for babies born as a result of egg freezing. However, more research is needed on the safety of egg freezing.

If you're considering freezing your eggs, look for a fertility clinic with expertise in the field. Experts are commonly known as reproductive endocrinologists.

The Centers for Disease Control and Prevention and the Society for Assisted Reproductive Technology provide information online about U.S. fertility clinics' pregnancy and live birth rates, although data related to pregnancies using frozen eggs is limited. Keep in mind, however, that a clinic's success rate depends on many factors, such as the ages of the women it treats.

If the expense of egg freezing concerns you, ask for information about the costs associated with each step of the procedure and the annual storage fees.

Before beginning the egg-freezing process, you'll likely have some screening blood tests, including:

• Ovarian reserve testing. To determine the quantity and quality of your eggs, your doctor might test the concentration of follicle-stimulating hormone and estradiol in your blood on day three of your menstrual cycle. Results can help predict how your ovaries will respond to fertility medication.

  Another blood test and an ultrasound of the ovaries might be used to get a more complete picture of ovarian function.

• Infectious disease screening. You'll be screened for certain infectious diseases, such as HIV and hepatitis B and C.

Egg freezing has multiple steps — ovarian stimulation, egg retrieval and freezing.

Ovarian stimulation

You'll take synthetic hormones to stimulate your ovaries to produce multiple eggs — rather than the single egg that typically develops monthly. Medications that might be needed include:

• Medications for ovarian stimulation. You might inject medication such as follitropin alfa or beta (Follistim AQ, Gonal-f) or menotropins (Menopur).
• Medications to prevent premature ovulation. Your doctor might prescribe an injectable gonadotropin-releasing hormone agonist such as leuproline acetate (Lupron Depot) or a gonadotropin-releasing hormone antagonist such as cetrorelix (Cetrotide).

During treatment, your doctor will monitor you. You'll have blood tests to measure your response to ovarian-stimulation medications. Estrogen levels typically increase as follicles develop, and progesterone levels remain low until after ovulation.

Follow-up visits will also include having vaginal ultrasound — a procedure that uses sound waves to create an image of the inside of your ovaries — to monitor the development of fluid-filled sacs where eggs mature (follicles).

When the follicles are ready for egg retrieval — generally after 10 to 14 days — an injection of human chorionic gonadotropin (Pregnyl, Ovidrel) or another medication can help the eggs mature.

Egg retrieval

Egg retrieval is done under sedation, typically in your doctor's office or a clinic. A common approach is transvaginal ultrasound aspiration, during which an ultrasound probe is inserted into your vagina to identify the follicles.

A needle is then guided through the vagina and into a follicle. A suction device connected to the needle is used to remove the egg from the follicle. Multiple eggs can be removed, and studies show that the more eggs retrieved— up to 15 per cycle — the better the chances of birth.

After egg retrieval, you might have cramping. Feelings of fullness or pressure might continue for weeks because your ovaries remain enlarged.

Freezing

Shortly after your unfertilized eggs are harvested, they're cooled to subzero temperatures to preserve them for future use. The makeup of an unfertilized egg makes it a bit more difficult to freeze and lead to a successful pregnancy than does the makeup of a fertilized egg (embryo).

The process most commonly used for egg freezing is called vitrification. High concentrations of substances that help prevent ice crystals from forming during the freezing process (cryoprotectants) are used with rapid cooling.

After the procedure

Typically, you can resume normal activities within a week of egg retrieval. Avoid unprotected sex to prevent an unintended pregnancy.

Contact your health care provider if you have:

• A fever higher than 101.5 F (38.6 C)
• Severe abdominal pain
• Weight gain of more than 2 pounds (0.9 kilograms) in 24 hours
• Heavy vaginal bleeding — filling more than two pads an hour
• Difficulty urinating

When you want to use your frozen eggs, they'll be thawed, fertilized with sperm in a lab, and implanted in your or a gestational carrier's uterus.

Your health care team might recommend using a fertilization technique called intracytoplasmic sperm injection (ICSI). In ICSI, a single healthy sperm is injected directly into each mature egg.

The chances of becoming pregnant after implantation are roughly 30 to 60 percent, depending on your age at the time of egg freezing. The older you are at the time of egg freezing, the lower the likelihood that you'll have a live birth in the future.