How do people freeze embryos?
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 lab uses a process called cryopreservation. It involves replacing the water in the cell with a substance called a cryoprotectant.
The embryos were left to incubate in increasing levels of cryoprotectant before freezing them.
After removing most of the water, the lab cools the embryo to its preservation state. They then use vitrification for freezing:
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 lab stores the embryos in liquid nitrogen.
Success rates of thawing frozen embryos
The process of thawing an embryo after cryopreservation has a relatively high success rate, and research suggests that women who use thawed embryos have good chances of delivering healthy babies.
According to a comparative study and review published in 2016, babies born after cryopreservation showed no increase in developmental abnormalities. However, the medical community still requires more long-term follow-up studies.
Some research indicates that, compared with slow freezing, vitrification increases an embryo’s chance of survival, both at the freezing stage and during thawing.
How long can embryos stay frozen?
In theory, a correctly frozen embryo can remain viable for any length of time.
The embryos remain in sealed containers at temperatures of -160 degrees centigrade. At this temperature, almost no biological processes, such as aging, can occur.
There are examples of successful pregnancies resulting from eggs that people have stored for up to 10 years. No long-term research into embryo freezing exists because doctors have only been carrying out the procedure since 1983.
Frozen or fresh embryos?
A study published in the International Journal of Reproductive Biomedicine looked at the results of over 1,000 instances of embryo transfer involving either fresh or frozen embryos.
The researchers found no statistical difference between the types of embryos, in terms of pregnancy rates or fetal health. The authors pointed out that people could use frozen, but not fresh, embryos for additional transfers in the future.
Other studies suggest that transferring frozen embryos may be more effective.
Results of research published in 2014 indicate that frozen embryo transfer might lead to a higher rate of pregnancy and better outcomes for both the woman and baby.
Who can benefit?
Embryo freezing may be a better option for certain groups, such as:
- people with genetic disorders that affect reproduction
- people who will soon undergo chemotherapy
- people who take medications that affect fertility
People who are approaching an advanced reproductive age and who are not yet ready to have children may also benefit from freezing embryos for later use.
In a freeze-all cycle, a doctor extracts an embryo, freezes it, and stores it.
People may benefit from this process if they have a higher risk of ovarian stimulation syndrome. This is a rare and potentially dangerous condition that can arise when a person is receiving stimulating hormones to increase egg production.
To reduce the risk of this condition, we may recommend freezing the embryo and transferring it when the ovaries are no longer stimulated.
We can also use a freeze-all cycle to test an embryo for a genetic disorder. This involves removing a few strands of DNA and testing the chromosomes.
Embryos with a standard set of chromosomes are more likely to transfer successfully. Prescreening can ensure that future offspring have a lower chance of developing genetic diseases.
Embryo freezing is relatively safe and often leads to a successful pregnancy and delivery.