The aim of every IVF treatment is to achieve pregnancy in the quickest and most comfortable way possible for our patients. Therefore, when a treatment begins, the goal is the transfer of one or two top-quality embryos into the uterus of the recipient mother.
In some cases, at the embryo transfer stage, the patient has a large number of good quality embryos available. It is not possible to transfer all of them due to the risk of multiple pregnancies.
These viable embryos that are not used for the transfer are frozen in order to be used at a later date. They can be used if the couple decides to try for another child or subsequently if fresh embryo transfer fails.
Embryo cryopreservation/ Embryo freezing is a well-established form of assisted conception treatment. The first frozen embryo baby was born in 1984. Embryo cryopreservation allows multiple embryo transfers from a single egg collection and improves the chances of live birth. The embryo is frozen using liquid nitrogen which stops all biological processes. The embryo is in a state of suspended animation and stays in this state until it is needed.
The embryo is then slowly thawed out and its biological processes reactivated.
Embryo freezing is not always carried out in every IVF cycle. In most treatments soft stimulation is used in order to obtain an adequate number of eggs causing minimum discomfort to the patients. In this case, spare embryos are not generated.
Not all embryos are viable for freezing. Although there may be several embryos in the laboratory, the embryologist can see which of them would not survive the freezing and defrosting process. These embryos are not frozen. We only freeze embryos where there is a reasonable possibility of survival after the defrosting process.
Some frozen embryos unfortunately do not survive the defrosting process. This means that even though we start a treatment, it does not necessarily mean that we will eventually have embryos to transfer to the uterus.
Pregnancy rates obtained using frozen embryos are similar to the ones achieved using fresh embryos.
The treatment that the patient needs to undergo in order to carry out a frozen embryo transfer is quick, simple and comfortable. Few injections are required. It takes no longer than two weeks and there is no need for frequent monitoring (usually no blood tests are required and normally no more than one ultrasound scan is necessary).
Pregnancies following this treatment proceed normally. The occurrence of complications is no higher than in any other kind of treatment or natural pregnancy. There is no link associated with this treatment to malformations and/or the physical and intellectual development of the child.
Frozen embryos are stored for periods of five years. If the couple decides to end storage, they have four options: use the embryos themselves for a further IVF treatment, donate the embryos to another couple, donate the embryos to scientific research or destroy them.
Indications of freezing embryos
Approximately 50% of women may have spare embryos available for freezing.
Freezing all embryos for subsequent transfer may be advised for women who are at a high risk of developing severe ovarian hyperstimulation syndrome following ovarian stimulation for in-vitro fertilization (IVF).
When embryo implantation may be compromised in cases such as the presence of endometrial polyps, poor endometrial development, break through bleeding near the time of embryo transfer or illness.
Difficulty encountered at fresh embryo transfer e.g. cervical stenosis (inability to pass through the cervical canal because the cervix is narrowed or scarred, etc).
Cryopreservation of embryos is very important to be incorporated in the egg donation programs. It is not always possible to synchronize the recipient’s cycle with that of the egg donor.