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Sperm, Eggs & Embryo Freezing

By Dr. Kirsten Small


The concept that sperm might be frozen and used to achieve a pregnancy at some later point in time has actually been around since the 1770’s, when an Italian priest called Spallanazani began to understand that in animals both an egg and a sperm are required for conception to occur.

It wasn’’t until the development of modern equipment and techniques during the 50’s that semen freezing became a reality. The small cell size and vast numbers of sperm in a semen sample make semen a relatively easy target for cryopreservation. The larger cell size and the multicellular nature of the embryo was more of a challenge. It was not until the 1980’s that the techniques for cryopreservation of embryos where perfected. The world’s first pregnancy from a frozen embryo was achieved in Australia in 1983 by Dr Alan Trounsen.

More recent work has focused on the oocyte as a possible target for cryopreservation. Australia has again led the way but the success rates of oocyte cryopreservation have been so low as to not make it a clinically viable procedure until more recent times. It is still early days for oocyte cryopreservation with less than 1000 reported pregnancies world wide, but with ongoing research it will probably become a mainstream procedure in the next ten years.

How Is Freezing Done?

Freezing cells usually results in their destruction due to the formation of ice crystals within the cells that then shatter the delicate structures within. The clue to successful freezing is to find a suitable cryopreservative. These essentially work by pulling water out of the cells so that crystal formation doesn’t occur. In IVF work, we use a combination of propanediol and dextrose for this purpose. Once frozen, the samples are stored at a very chilly minus 150 degrees in liquid nitrogen.

To thaw a sample it is simply removed from the storage tank and placed in a warm bath to very rapidly bring the sample back to body temperature. The sample is then washed in culture medium to remove any residual cryoprotectant prior to clinical use.

The Advantages Of Using Cryopreservation

There are many reasons why cryopreservation has now become part of the standard practice in fertility clinics around the world. It allows men the ability to store semen samples for future use when they are about to have a treatment that can affect their future fertility, such as chemotherapy or even vasectomy. It facilitates the use of donor sperm, as the sample can be quarantined while the donor is screened for viral infections. It is easy to transport to remote locations, and means that the sample is always available when it is required.

Embryo cryopreservation has helped to reduce the rate of multiple pregnancies in IVF as there is less pressure to use all the embryos from a single IVF cycle within that cycle, and permits an ongoing pregnancy rate after IVF with frozen embryo transfer cycles which are cheaper, easier, and carry less risk for the woman.

Cryopreservation of eggs (oocytes) has opened up new opportunities and also new ethical dilemmas. A woman who is about to undergo treatment that is likely to result in the loss of ovarian function, such as pelvic radiotherapy, can now have an IVF cycle and collect eggs for storage – if time and her health permit. Single women who are increasingly aware of the significance of the biological clock are asking if they can store eggs at a younger age to help guard against later infertility.

Our View On Semen, Embryo & Egg Freezing

Fertility Solutions offers semen, embryo and egg freezing programs. While we are able to offer egg freezing, our experience with this technique is still growing and we are careful not to give women a false expectation about the chance of future pregnancy with this technique.

If you would like to know more please give us a call and come in for a chat – 1300 337 845 (1300 FERTILITY).