What is in vitro fertilization (IVF)?
Many women and their partners try for a long time to get pregnant, but can’t. Some may turn to the process of in vitro fertilization (IVF) to help them have a baby.
With IVF, a woman’s egg cells and a man’s sperm cells are put together in a dish in a special fluid in the laboratory. The new cell that is made when an egg cell and a sperm cell combine is called an embryo. The doctor then transfers the embryo into the woman’s uterus (womb). The embryo implants (attaches) to the wall of the uterus, where it develops and grows into a baby.
As part of the IVF process, the woman is given special drugs that cause her ovaries to release more egg cells than normal. The man also gives a high number of sperm cells. With many egg and sperm cells to work with, several embryos are often made. The doctor will transfer one to four embryos, based mainly on the woman’s age, into her uterus to lower the chances that she will have more than one baby. That means there may be some embryos left over.
What is embryo cryopreservation?
Embryo cryopreservation is the process of freezing and storing the extra embryos. The embryos are then thawed and used at a later time. Embryo cryopreservation is a vital part of most IVF programs. According to the National Embryo Donation Academy, there were approximately 500,000 embryos in storage in the United States in 2011.
Why is embryo cryopreservation done?
There are many reasons a man and woman might choose to freeze and store their embryos:
- They may feel it is a better option than having the extra embryos destroyed.
- It can provide another chance to get pregnant if the IVF process fails the first time. The couple will not have to go through IVF again.
- If the man and woman have a baby, they can use the embryos later to have a second baby.
- The woman can save embryos before she begins treatments, such as for cancer, that might reduce or eliminate her chances of getting pregnant.
- The embryos could be saved and given to someone else in a donor program.
- The embryos could be saved and donated for research.
How is embryo cryopreservation done?
A cell is made up mostly of water. The main concern when freezing embryos is ice forming in and between the cells. Ice crystals can hurt the cell wall, and can harm the small structures inside the cell.
The embryo must be protected during the freezing process. This is done using special fluids called cryoprotective agents (CPAs). CPAs are like “anti-freeze” for cells.
Doctors use two different methods to freeze and preserve embryos: slow programmable freezing and vitrification.
In the slow freezing method, the embryos are frozen slowly, in stages. The CPAs are added to the embryos in increasing strengths over 10 to 20 minutes. Then the embryos are slowly cooled over two hours in a machine that lowers the temperature minute by minute. Once frozen, the embryos are stored in liquid nitrogen at -321° Fahrenheit (-196.1° Celsius).
Vitrification is a rapid freezing technique that uses much higher strengths of CPAs. With this method, the doctor first mixes the CPAs with the embryos. CPAs that are very strong can also hurt the cell. To prevent this, the embryos are quickly placed into the liquid nitrogen. This process changes them into an almost-solid state, like glass. In this state, ice is unable to form.
When needed, the embryos are slowly thawed. They are soaked in special fluids to remove the CPAs. This also restores the cell’s normal water balance.
When is embryo cryopreservation done?
Embryos are often frozen from one to six days after they are made.
How long can embryos be stored?
Once they are frozen, the embryos are stored in sealed liquid nitrogen freezers. Embryos can be frozen in liquid nitrogen for many years. It is not known how long embryos can be frozen safely and still be useful. Some countries have set time limits on how long embryos can be stored.
Risks / Benefits
How safe is embryo cryopreservation?
Research has shown that freezing and thawing embryos does not harm the baby. Children born from frozen embryos have no greater rate of birth defects or health problems than children born from embryos that were not frozen.
Recovery and Outlook
Does embryo cryopreservation work?
Many healthy babies have been born from embryos that were frozen and thawed. Some babies have been born from embryos frozen for more than 10 years. IVF programs with good cryopreservation techniques have the same pregnancy rates with fresh and frozen embryos.