Egg freezing (unfertilized egg freezing) is the process of freezing eggs before they are fertilized. It is sometimes confused with "fertilized egg freezing," which is freezing after fertilization. We will introduce the two types of freezing: egg freezing (unfertilized egg freezing) and fertilized egg freezing.
What is the Egg freezing?
Egg freezing is the process of freezing and preserving eggs collected from the ovaries.
It is also called unfertilized egg freezing because the egg used is an unfertilized egg before it is fertilized by sperm. Most of them are for unmarried women.
There are two types of freezing: one is for medical reasons, such as preserving the fertility of patients with malignant tumors whose ovarian function may decline as a result of the treatment.
And the other reasons may be social, such preserving the fertility of patients who are healthy but whose reproductive capacity is declining due to aging and other factors.
What is the fertilized egg freezing?
Fertilized egg freezing is the process of freezing and preserving an egg that has been fertilized with sperm and has undergone normal cell division.
Fertilized egg freezing is performed as part of the IVF process for fertility treatment, and also for couples who do not wish to have children at this time but wish to have children in the future, or for married couples or couples in Common law marriage to freeze their fertilized eggs in advance in case their fertility declines due to aging.
If you wish to have a child in the future, you can expect a higher pregnancy rate if you cryopreserve a fertilized egg than if you cryopreserve an egg or sperm alone.
Cryopreservation of eggs at a young age can prolong their fertility. The graph below shows the 2018 Japan Society of Obstetrics and Gynecology national pregnancy rates.
As women age, their pregnancy rate decreases, and conversely, their miscarriage rate increases.
However, cryopreservation of eggs at a young age can be expected to maintain the pregnancy and miscarriage rates of the age at which the eggs were frozen.
In vitro fertilization at age 42
When an egg is retrieved at the Mother’s age of 42 and undergoes IVF, the pregnancy rate is about 20% and the miscarriage rate is about 44%. The aging of eggs begins to progress rapidly around the age of 34, so transferring eggs that have aged to the age of 42 years will not result in a high pregnancy rate and will result in a high miscarriage rate.
In vitro fertilization at age 42 using eggs frozen at age 34
Even if you do IVF at the age of 42, if the eggs you use were cryopreserved at the age of 34, before the aging process, you can expect a pregnancy rate of about 40% and a miscarriage rate of about 18%, which is equivalent to the age at which the eggs were frozen (34), rather than the current age of the mother.
* Pregnancy rates are from the ART Data Book of the Japanese Society of Obstetrics and Gynecology.
Why does it become more difficult for women to get pregnant as they age?
There are two main reasons.
(1) Because the number of eggs are limited and decreases with the age.
(2) As the egg itself ages, it becomes more prone to abnormal cell division, which makes it more difficult to have a healthy baby.
The eggs of young women have a higher probability of normal cell division because the eggs themselves are young. An egg that has undergone normal cell division has 23 chromosomes. This is fertilized by a sperm with 23 chromosomes, resulting in 46 chromosomes in fertilized eggs. This fertilized egg will lead to pregnancy and the birth of a healthy baby.