Embryo Freezing



Fertilisation takes place when a sperm enters an egg. The fertilised egg is called an embryo. The resulting embryo may be viewed as potential human life, or in the view of some, a human life.


Following human In Vitro Fertilisation, embryos may be produced in the laboratory which cannot be immediately replaced into the uterus. We offer the patient an opportunity to cryopreserve (freeze) normally developing embryos for future use.


Who would benefit form Embryo Freezing?


Embryo Freezing (Cryopreservation) is an important dimension of the IVF cycle. There are times when patients have additional healthy embryos and want them frozen for various reasons including:


  • Wanting a second or a third opportunity for pregnancy without having to go through the ovarian stimulation and egg retrieval process again
  • Efficient use of each frozen embryo, thus minimising embryo attrition
  • Avoiding ethical dilemmas by eliminating the need to dispose of embryos
  • Reducing the need to transfer too many embryos and risk multiple gestation pregnancies
  • Increasing the number of pregnancies possible per retrieval cycle


Traditional technique vs Vitrification 


Traditionally, embryo cryopreservation is performed using a “slow cooling” or “slow freezing” process that offers a cleavage survival rate of 68%, according to research published in the Journal of Assisted Reproduction and Genetics.


However, during the slow freezing process, ice crystals often forms within the cell(s)and that would destroy the cell’s integrity.


We use the pioneer “flash freezing” technique called “Vitrification” for egg freezing (oocyte cryopreservation). This innovation rapidly freezes the cells in order to avoid intracellular ice formations that cause cell damage, and to increase the embryo survival rate to over 88% according to the study.


Depending on the development of the embryo, we use the most optimal freezing method to ensure the highest chance of success.


How does it work?


Embryos are frozen in the In Vitro Fertilisation laboratory in special holding containers (freezing straws) in which they are suspended in a small volume of supporting medium and a special freezing solution (cryoprotectant).


During the freezing process, the embryos are brought to a temperature of -196º C. They are then submerged in liquid nitrogen in storage tanks. The embryos can be kept in liquid nitrogen indefinitely.


Embryos may be frozen at any stage of development, from one cell to blastocyst (100 cell), or from one to five days after fertilisation.


For frozen embryos to produce a pregnancy, they must be thawed and then put back into the uterus at the correct time of the menstrual cycle. Therefore, the day of embryo replacement varies with the stage at which the embryos are frozen.


The transfer of previously frozen embryos is electively scheduled and you will be instructed as to the exact day of the cycle when the embryos will be replaced. It is not uncommon for a patient to have groups of frozen embryos cryopreserved at different stages and requiring different cycles of frozen embryo transfer.


Success rate


When embryos are frozen, their likelihood of producing a pregnancy is reduced. However, patients who fail to achieve pregnancy with fresh embryos may become pregnant during subsequent embryo transfers using their frozen embryos. A small proportion (about 20%) suffer sufficient damage during freezing that at the time of thawing, they are no longer viable.


Rarely, all of a couple’s frozen embryos are found to be non-viable and the transfer is cancelled. In order to have a reasonable chance of producing a pregnancy after thawing, the embryo must demonstrate normal development and appearance (“morphology”).


Embryos can be stored indefinitely without a compromise in their quality, according to the Society for Assisted Reproductive Technology. Embryos frozen using vitrification have virtually the same viability for uterine attachment (pregnancy) as freshly harvested eggs.