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Freezing Eggs, Embryos & Sperm

Freezing Eggs

Freezing Sperm

Freezing Embryos

Freezing Eggs

Over the last few decades the cryopreservation of sperm and embryos using the “slow” freezing process has been quite successful because a sperm cell is small and the genetic material contained in an embryo is already combined with that from the sperm cell making it more stable.

The relative difference between the size of an egg cell compared to the size of a sperm cell can be seen by clicking Egg Size vs Sperm Size (opposite).

Cryopreservation of embryo and sperm cells is done by cooling cells and whole tissues to low sub-zero temperatures, typically -196 oc, so that biological activity, including the biochemical reactions that lead to cell death, is effectively stopped. Preventing damage from frost during the freezing process requires surrounding the cells with cryoprotectants, or toxic chemicals like antifreeze.

Until recently human eggs have not responded so well to the slow freezing process and the process has been problematic. Unlike a sperm cell a human egg is the largest cell in the body and therefore full of water which expands when it freezes. In an uncombined state the human egg cell is also very delicate and unstable. To minimise ice crystal formation, the water inside the cell has to be extracted as the temperature drops below freezing point to prevent damage from occurring to the egg cell’s genetic material.

Vitrification Process

A significant development in the field of Assisted Reproductive Technology is the successful freezing (cryopreservation) of unfertilised human eggs cells which has made the freezing of human egg cells more viable.

There are many reasons for freezing human egg cells:

Medical Reasons

  • Compromised ovarian reserve/score (low egg  supply/poor quality eggs)
  • Women undergoing chemotherapy or pelvic radiation treatment for cancer
  • Surgery (e.g. severe endometriosis)
  • Genetic Conditions – e.g. Turner Mosaic and Fragile X syndrome
  • Egg Banking for research or donation/egg sharing

Social Reasons

  • To allow a woman to delay child-bearing and develop her career first.
  • Women wanting to preserve her eggs while waiting for “Mr Right”.
  • Couples waiting for financial stability before starting a family.
  • Choice to freeze eggs while at optimum fertility for later use.

When undergoing IVF (in-vitro fertilisation) the success rate of live births also declines with age.

A chart showing the rate of decline can be seen by clicking “Decline in IVF Success with Age” link opposite.

More details about recent developments that have made the rapid freezing of human egg cells more successful in achieving successful live births can be found on the next page.

There are a variety of conditions that cause ovulatory dysfunction. Fertility drugs and IVF (in-vitro fertilisation) are possible solutions.

Freezing Sperm

Fallopian Tubal Blockage

The process of cryopreservation is especially ideal for sperm. Sperm cells have been frozen and thawed successfully for more than forty years. The sperm can then be used in the future to inseminate eggs via intrauterine insemination (IUI) or by the IVF process.

Why Freeze Sperm?

When facing medical treatment that may affect their fertility, men may wish to freeze their sperm for use after their treatment has finished. For example, some forms of cancer treatment such as radiology or chemotherapy will likely damage sperm cells.

Men who are about to undergo a vasectomy may wish to keep their options open to be able to have children in the future.

Men that have a low sperm count or producing sperm that are deteriorating in quality over time may wish to freeze their sperm while they are still viable for future use.

Men who have difficulty producing a sperm sample on the day fertility treatment is to take place could have their sperm thawed on the day required.

When sperm are donated freezing also allows the sperm to be quarantined for six months whilst the donor is screened for infections.

What happens when sperm are frozen?

Before freezing the donor will be screened for infectious diseases, including HIV and Hepatitis B and C. Written consent will then need to be given for the sperm to be stored. A fresh sample of sperm will then be frozen and stored in tank containing liquid nitrogen. Like cells and other whole tissues undergoing cryopreservation, sperm cells are preserved by cooling to sub-zero temperatures, typically -196C. The standard storage period is ten years.

Some sperm do not survive or are damaged during the freezing process. This means there may be a reduction in sperm quality and poor quality sperm can only be used for intra-cytoplasmic sperm injection (ICSI). 

Pros and Cons between Egg Freezing & Sperm Freezing:

Sperm Freezing

  • Non-invasive
  • Relatively inexpensive (£l00)
  • Highly effective (as good as fresh)
  • Long track record/standardised (1940s)
  • Medical indications accepted
  • Social indications accepted
  • Fertility preservation / convenience / donor

Egg Freezing

  • Comparatively invasive
  • Comparatively expensive (£l000)
  • Variable success
  • Not yet fully standardised (1986 onwards)
  • Medical indications accepted
  • Social indications not widely accepted
  • Fertility preservation
  • To see how frozen human eggs are stored please click on Storage of Human Eggs opposite.

Freezing Embryos

With improved cryopreservation techniques using vitrification now being used to freeze eggs and ovarian tissue are also being used to freeze embryos.  Studies show that embryos transferred in non-stimulated cycles, rather than directly following fresh egg collection, lead to an increase in pregnancy rates and more successful live births.

Spare Embryo Transfer

After a cycle of IVF using freshly collected embryos there is often a surplus of high-quality embryos that are not used.  This is because there may have been more than needed or they were not medically possible to be transferred during the cycle but are still viable and have a good chance of creating a successful pregnancy.
Freezing embryos allows them to be used at a later date. This could be for the very next cycle, without requiring a stimulated cycle, if necessary, or for a future brother or sister when planning a larger family.

Frozen Embryo Transfer (FET)

Fertility Assist uses an individualised IVF programme which involves freezing all good quality embryos left over from an IVF cycle to be used at a later date.  Frozen embryos can also be shared similarly to frozen eggs and can therefore also originate from a donor’s egg cycle.


After thawing, an embryo is transferred, one at a time, during non-stimulated cycles.  This maximises live birth rates at each IVF attempt while minimising multiple pregnancies which can increase health risks for both mother and the baby.

Storing Human Eggs

Under Human Fertilisation & Embryology Authority regulations there is a storage window of ten years that is allowed for a woman’s eggs to remain frozen. If, however, the woman for whom the eggs are stored has, or is likely to develop significant and premature infertility, this period can be extended.

Sharing Human Eggs

Due to the shortage of donor eggs, waiting lists at fertility clinics are long. Egg donation offers hope for a large number of women who previously thought they could never have children. For example older women or women who may have experienced premature menopause.  Others may have undergone chemotherapy or radiotherapy.  Women who are carriers of a genetic disorder may not wish to pass their condition on to their children.

Egg sharing programmes enable women who have viable eggs, but need fertility treatment for other reasons, to share their eggs with other women who require donated eggs to conceive. The egg sharer is not charged for her own IVF treatment or is offered treatment at a vastly reduced cost in return for her donated eggs.

Egg-sharing usually involves the synchronisation of the cycles of two women, the egg donor and the recipient, using fresh eggs. With the improvement in freezing techniques, it is becoming more feasible for frozen eggs to be used as well., therefore egg sharing programmes can also enable women willing to share their eggs the chance to freeze their eggs for future use as an alternative to immediate IVF treatment. The live birth rate for all egg sharing and donation programmes throughout most of Europe and the USA is currently around 50.5%.

To book an appointment or virtual consultation

All Clinics are held at Harley Street except HCA Healthcare patients who are seen at the London Bridge Hospital at The Shard or at Portland Hospital for Women & Children.