Embryo freezing is a procedure that allows people to store embryos for later use. A person can also freeze eggs, which are not fertilized. An embryo forms after fertilization and after the cells start to divide.
Before freezing can take place, people need to create suitable embryos. To do so in the laboratory, doctors must harvest and fertilize some eggs.
First, the person will take hormones to make sure that ovulation happens on schedule. They will then take fertility medications to increase the number of eggs that they produce.
In the hospital, a doctor will extract the eggs, using an ultrasound machine to ensure accuracy.
A person may wish to freeze their eggs. Or, they may wish to use them at once to become pregnant. In this case, the doctor may recommend in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI).
During IVF, the doctor exposes the eggs to sperm and leaves them in a laboratory for fertilization to take place. After this, the correct term for a fertilized egg is an embryo.
During ICSI, the doctor extracts the eggs and injects a single sperm directly into an egg.
They may do this if there is a problem with the sperm or if past attempts at IVF have not resulted in fertilization. The doctor may use one embryo and freeze the others.
The main aim of freezing embryos is to preserve them for later use.
The biggest challenge is the water within the cells. When this water freezes, crystals can form and burst the cell.
To prevent this from happening, the doctor uses a process called cryopreservation. It involves replacing the water in the cell with a substance called a cryoprotectant.
The doctor then leaves the embryos to incubate in increasing levels of cryoprotectant before freezing them.
After removing most of the water, the doctor cools the embryo to its preservation state. They then use one of two freezing methods:
Slow freezing : This involves placing the embryos in sealed tubes, then slowly lowering their temperature. It prevents the embryo's cells from aging and reduces the risk of damage. However, slow freezing is time-consuming, and it requires expensive machinery.
Vitrification : In this process, the doctor freezes the cryoprotected embryos so quickly that the water molecules do not have time to form ice crystals. This helps protect the embryos and increases their rate of survival during thawing.
After the process of freezing is complete, the doctor stores the embryos in liquid nitrogen.
Embryo freezing may be a better option for certain groups, such as:
people who take medications that affect fertility
A frozen embryo transfer (FET) is a cycle where a frozen embryo from a previous fresh IVF cycle is thawed and transferred back into a woman's uterus. This means you won't have to undergo another cycle of hormone stimulation and an egg collection. Frozen embryo cycles can be undertaken on your natural cycle or using hormone preparation, or ovulation induction
Sometimes during an IVF cycle, we’ll be able to create more than one embryo. We’ll usually recommend transferring one, and freezing the others. This is due to the serious risks associated with multiple pregnancies if you transfer more than one embryo at a time.
Embryo freezing gives you more opportunities for a pregnancy for each hormone stimulation cycle and egg collection. If you do not become pregnant from the first transfer from that cycle, we can transfer a frozen embryo during a frozen embryo transfer cycle.