The process for both IVF (in vitro fertilization) and egg freezing to a large extent is the same. The main differentiating feature is the intent with which the process is performed. In IVF, the eggs are grown and fertilized with a partner’s semen to obtain an embryo, which if implanted into the uterus, may result in a pregnancy and live birth, contributing to IVF success. Egg freezing however implies that the eggs are grown and retrieved in the same manner as in IVF, but they are not fertilized. They are stored as female gametes or eggs in liquid nitrogen in a frozen stage to be used at a later date. When a pregnancy is desired, they can be thawed and fertilized with semen and the resulting embryo can be transferred to the uterus with a hope to achieve pregnancy.
The process of egg retrieval
In a natural cycle of the ovary, which we know as a menstrual cycle (time from day 1 of a period to day 1 of the next period) sees the growth of only one egg, rarely two, in a given cycle. In IVF, since we want to retrieve more eggs from the ovary in a cycle, we overstimulate the ovary with hormones. These are the same hormones which are produced in the body, but in a natural cycle, the ovary makes only so much hormone which is enough to support the growth of one egg. In IVF, the same hormones are administered as injections to make more eggs grow and mature. The follicles, which are small fluid sacs filled that contain eggs) are monitored by ultrasound for their size. Once the size of the follicles seems to be appropriate to yield mature eggs, a final injection for egg maturation is given, and the eggs are retrieved with ultrasound guidance under a short anesthetic after 34-36 hours after the last injection.
Egg freezing is done for various indications:
Social egg freezing – It can be done for social reasons wherein eggs are retrieved and frozen for future use. Girls freeze their eggs because they have not found a suitable life partner and fear that they may lose fertility by the time they find someone.
Before cancer treatment – Chemotherapy can cause premature ovarian failure and fertility preservation should be therefore discussed and offered to all premenopausal women who need chemotherapy to treat their cancer.
Endometriosis – It tends to affect the ovaries resulting in endometriotic or chocolate cysts which cause fibrosis and deplete the egg reserve of the ovaries. If cysts are large, surgical removal may be required which further reduces the egg reserve. Therefore, young girls who are single or for some reason cannot plan pregnancy may decide to go for egg freezing.
How many eggs do I need to freeze?
Every egg that is retrieved from the ovary will not get fertilized, every embryo formed after fertilization will not grow, and every embryo transferred to the uterus will not get implanted. Even if implantation is successful, not every pregnancy will result in a live birth. This means that there is attrition at every stage. It increases with the woman’s age, because as the age advances, not only the quantity, but also the quality of eggs deteriorates. So, the pregnancy rates decline and miscarriage rates increase as the woman’s age increases.
So how many eggs should be frozen to have a realistic chance of a baby? To help the IVF specialist in counselling women opting for egg freezing, American scientists developed a prediction model which showed that for a 50%, 80% or 95% chance of having a baby from eggs frozen from a woman age 35 or less is 6, 14, and 30 eggs respectively.
When should I go for egg freezing?
In light of the number of eggs required, the younger the woman, more are her chances of pregnancy and live birth. But certainly, it is desirable to go for freezing before age 35.
