Egg freezing
How egg freezing works, what to expect from stimulation to storage, and why the age at which you freeze matters most.
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If you’re thinking about freezing your eggs to delay having a baby or to preserve your fertility, you are not alone. Many women today decide to start their families later for personal or career reasons, and more women are having children in their 30s and 40s.
Why women freeze their eggs
Egg (oocyte) freezing has become a common fertility choice. It lets you save eggs while you’re younger, when they tend to be more plentiful and healthier, and use them to have a child when you’re ready. Research on when women choose to have children points to being in a secure relationship, feeling in control of one’s life and feeling prepared to parent.
Far from encouraging women to wait, I found that egg freezing made it easier for women to relax and find a partner.
Egg freezing can also:
- Preserve fertility for women at risk of losing it because of cancer treatment or chemotherapy for other conditions, such as lupus nephritis
- Provide an option when no sperm are found after surgical sperm retrieval in men with severe male factor infertility
Frozen eggs belong solely to the woman who produced them. They are not under the joint custody of a couple.
Age matters most
Egg freezing has a higher chance of leading to a baby when eggs are frozen earlier in life, ideally before about age 38. Pregnancies have been reported from eggs frozen into the early 40s, but the chance of success declines with each year. The number of mature eggs frozen also matters: freezing more mature eggs improves the chance of having a baby later.
How egg freezing works
The human egg is a special cell. It is the largest cell in the body and has a high water content. Its outer membrane is less permeable than that of other cells, and its chromosomes are spread along a delicate structure called the spindle rather than enclosed in a nucleus. These features are why the freezing method matters.
- Ovarian stimulation. You take medication, by mouth or by injection, that stimulates your ovaries to mature more eggs than usual. Your fertility specialist monitors your response and adjusts the dose as needed.
- Egg retrieval. After several days of stimulation, you are sedated and your eggs are retrieved with a needle guided by vaginal ultrasound. Most women return to work the same or the next day.
- Freezing. Your eggs are frozen and stored in liquid nitrogen. Frozen eggs can be stored for a very long time and can be moved in liquid nitrogen to a long-term storage facility.
Rapid freezing and slow freezing
There are two methods for freezing eggs.
Rapid freezing (vitrification)
The temperature is lowered very quickly to -196°C, so water has no time to form ice crystals that could damage the egg. Vitrification is done a few hours after retrieval. The eggs are placed in a small volume of solution with a high concentration of protective agents (cryoprotectants), loaded onto a special device, sealed and plunged into liquid nitrogen. Eggs frozen this way survive thawing much better than eggs frozen slowly. NYC IVF uses vitrification.
Slow freezing
The egg is placed in a solution that protects it from ice damage, and the temperature is lowered gradually. Fewer eggs survive thawing after slow freezing than after vitrification.
When you’re ready to use your eggs
When you’re ready, the lining of your uterus is prepared. Your eggs are thawed (warmed) and fertilized using ICSI, where one sperm is injected into each egg. You can use partner or donor sperm. The resulting embryos are then transferred to your uterus, usually one or two at a time.
This part of the process doesn’t require injections for egg production or anesthesia. We monitor the lining of your uterus with ultrasound.
What affects results
A successful outcome doesn’t end with a frozen egg. Each egg also needs to:
- Survive thawing
- Fertilize after a sperm is injected
- Develop into a healthy embryo
- Implant after the embryo is transferred to the uterus
The age at which eggs are frozen is the most influential factor in the chance of pregnancy. The freezing method also matters, with vitrified eggs giving a better chance than slowly frozen eggs, and the chance of a baby increases with the number of mature eggs frozen. That is why we recommend considering egg freezing at a relatively younger age.
Studies so far suggest that babies born from frozen eggs have outcomes similar to naturally conceived children, although long-term follow-up studies are still limited.
This article is general information, not medical advice. Every situation is different, so talk with your doctor about yours.
