If you're thinking about freezing your eggs to delay having a baby or to preserve your fertility, you are not alone. Today, many women decide to delay starting their families for personal or career related reasons. In fact, in the past decade, pregnancy rates among women in their 20s declined while rates among women in their 30s and 40s increased.
As a result, egg (oocyte) freezing has become a common fertility choice among modern women. Egg freezing empowers women by allowing them to save their more abundant—and healthier—eggs while they’re young then use them to have a child when they’re ready. One study found that the factors that influence the time women decide to have a child are 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."
Sara Richards (WSJ, May 3, 2013)
Egg freezing can also be used for to preserve fertility in women at risk for losing their fertility due to cancer treatment or exposed to chemotherapy for other causes, such as lupus nephritis. And, it can be applied when no sperm were retrieved after surgical sperm harvest in men with severe male factor.
Before you decide freezing your eggs, you should know that this option has a higher potential to yield a baby when eggs are frozen earlier in life (before age 38). Pregnancies, however, were achieved up to age 44.
Frozen eggs are under the sole jurisdiction of the female that produced them and are not under the joint custody of the couple.
How egg freezing works
The human egg is a special cell. It is the largest cell in the body. The cell has high water content. It has a special membrane surrounding it that is less permeable than other cells. The egg chromosomes are spread on a flimsy structure called the spindle rather than enclosed within the nucleus.
When you undergo egg freezing, you will first receive a special medicine—either orally or by injection—that will help to stimulate your ovaries to increase the number of eggs produced. Your fertility specialist will monitor your response and modify the medication dose as needed.
After a few days of ovarian stimulation, you will be sedated and your eggs will be retrieved using a vaginal ultrasound and needle aspiration. Most women usually can return to work the same or next day following the procedure.
Your eggs will then be frozen using one of two methods:
Rapid freezing (vitrification): The temperature is lowered very quickly to -196°C so the water does not have the time to make ice crystals and damage the egg. Rapid freezing is performed four hours after retrieval. High concentrations of cryoprotecting materials are use. Eggs are placed in a small volume of solution. One or more eggs are transferred to a special device (cryotip, cryotop, cryoloop or cryoleaf). The device is sealed and then plunged into liquid nitrogen. Cryotop egg vitrification appears to yield the best outcomes. This is the method used by NYCIVF as eggs survive thawing better than slow freezing (>90% survival).
Slow freezing: The egg is placed within a solution that prevents it from being damaged by ice (cryoprotectant) and the temperature is lowered slowly. Frozen eggs can be stored for a very long time and can be transferred in liquid nitrogen to long term storage facility.
When you’re ready to use your eggs
When you are ready to use your eggs, the lining of your uterus will be prepared. Your eggs will then be thawed and fertilized using ICSI (injection of one sperm into each egg). The embryos will then be transferred into your uterus.
Partner or donor sperm can be used. During this process you will not require injections or anesthesia, only monitoring of the lining of the uterus using ultrasound. Approximately two or three embryos are transferred. Using vitrification, the majority of the eggs usually survive the thaw and about 70% fertilize with ICSI.
Results of egg freezing
It’s important to remember that successful egg freezing doesn’t end with the frozen egg. It also requires that the egg survive after thawing (warming), fertilize after injection with a sperm, develop into viable embryos, and sustain implantation after transfer of resulting embryos into the uterus.
Survival after thawing depends, in part, on the method used to freeze your eggs:
About 85-90% of eggs (oocytes) thawed after rapid freezing (vitrification) survive. This number is similar to the survival rate of thawed embryos. This is the method use by New York City IVF. About 60-70% of eggs thawed after slow freezing survive.
Among the surviving eggs, ICSI (sperm injection) results in the successful fertilization of approximately 75% of eggs. One or more embryos are then transferred into your uterus.
When it comes to a successful pregnancy after egg freezing, the age of the mother appears to be the most influential factor. In the largest study done to date, the ongoing pregnancy rate after egg freezing was 40% among women under the age of 35 but only 15-20% among women over the age of 35. Therefore, it is important to consider this technology at a relatively younger age (less than 38-40 years) Each year reduces your chance of delivery by 7%.
Egg freezing method also appears to have an impact on pregnancy success rates. A thorough review of the medical literature shows that each frozen egg has an 8-12% chance of producing a pregnancy if rapid freezing (vitrification) is used vs about 3% if slow freezing is used. Read more
The chance of obtaining a pregnancy is also markedly increased if more than 8 oocytes are rapidly frozen (vitrified). Each available mature egg increases the delivery rate 8%. Read more
For example: For a 35 year young female undergoing ovarian stimulation, an average of 10 oocytes is collected, with 80% of them being mature (8 eggs). When she is ready to have a baby, 5 eggs (or more) are warmed, with at least 4 eggs expected to survive. An injection of one sperm into each egg is expected to result in at least 3 embryos. Two of those embryos are expected to be of good quality and are transferred to the uterus. Those are expected to yield a delivery rate of approximately 45%.The third embryo can be refrozen.
There is some indication in the medical literature that after slow freezing or vitrification of oocytes, the baby outcomes were similar to naturally conceived children, although there are no long-term follow up study.