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Freezing of embryos, Sperm, Eggs

Most people call it embryo freezing, but more correctly it is “embryo cryopreservation” because the ultimate goal is to store the embryo cryogenically and to preserve its viability for future initiation of pregnancy.

Before good embryo cryopreservation protocols were available, most IVF clinics had to discard any excess embryos left over after embryo transfer. Early embryo cryopreservation programs usually had limited success. Today, more successful protocols have been introduced that have made embryo cryopreservation much more successful. Many IVF children now have younger siblings that were conceived at exactly the same time, but born years apart due to the increased success of embryo cryopreservation.

Basic Principles of Embryo Cryopreservation and Thawing

There are now 2 types of Freezing technologies that are used in IVF laboratories.

The older technology is called SLOW FREEZING and until recently has been the gold standard.

The second and newer technology is called VITRIFICATION which is a rapid cooling method.

Both of these will be discussed below.

Slow freezing

The failure or success of embryo cryopreservation is dependent upon how successful or unsuccessful the removal of water has been from the individual cells of the embryo. If water is left in the cells, it forms crystals when frozen. These crystals act like knives and disrupt the inside of the cells of the embryo or “cut” through the outer layer or “membrane” of the cells. If this cutting or disruption has occurred, the embryo will not survive. In order to avoid the formation of the water crystals, a “cryoprotectant” is added which replaces most of the water inside the embryo. Under the proper conditions, the cryoprotectant will not form crystals and the embryo can safely withstand the drastic reduction in temperature required for cryogenic storage.

When the embryo is removed from cryogenic storage, for use, the reverse process must occur. The cryoprotectant is removed from the cells of the embryo and replaced back with water.

Even though an embryo may look strong and healthy, it may not be able to move water and cryoprotectant in and out of its cells efficiently. If this occurs parts of the embryo or all of the embryo will not survive the cryopreservation and thawing process.


This is a process which allows "glass like" solidification of a solution without ice crystal formation in the living cells. When a solution is cooled,·ice crystals will form -right up until·minus 130 degrees Centigrade.

Vitrification is like "flash Freezing" The embryos are plunged into liquid nitrogen at around· minus 200 degrees. The liquid therefore does not have time to form crystals and assumes a "glass like" state. Therefore there is no damage caused by ice crystals.

Up until recently there have been concerns about the safety of vitrification, however years of research and study have now reassured us that it is a process as safe as slow freezing.

Sperm Freezing

Sperm banking is the specialized cryopreservation and cryogenic storage of sperm for future use in reproduction.

Who would benefit from Sperm Banking?

A patient or a couple may wish to bank sperm for the following reasons:

• To use as a back-up in infertility treatment when the sperm quality is known to be variable

• When a man has difficulties collecting semen by masturbation

• To use in infertility treatment when the man may be absent during treatment (travels frequently or lives elsewhere)

• When sperm are being retrieved surgically from the man (e.g. “MESA”, “PESA” or “TESE” procedures)

• When the man is about to receive medical treatment such as chemotherapy or radiation which will/may affect his fertility

• For men in "high risk" occupations where they are at greater risk of testicular injury

Information reference:

Hours of Operation:Monday – Friday, 8 a.m. – 5 p.m.
Saturday, 8 a.m. – 12 p.m.
Sunday, By Appointment