Fertility preservation or elective egg freezing is becoming an increasingly popular option for women as they delay pregnancy to later in life for a multitude of reasons.

It’s well established the risk of infertility increases with age with the chance of infertility accelerating over the age of 35. The main reason for this is the reduction in the number of stored oocytes (eggs) in the ovaries. At the age of the 30 there are around 40,000 oocytes remaining while at the age of 40 there are less than 1000.

Egg freezing is now an accepted mainstream medical practice endorsed by the American Society of Reproductive Medicine and the American College of Obstetrician Gynaecologists following major advances in technology and success rates. In 2017 around 11000 American women froze their eggs.

Success rates for egg freezing (and subsequent thawing with fertilisation) have increased significantly and are now thought to be close to that of IVF with frozen embryos.

While not being a perfect guarantee, egg freezing significantly increases the chance of being able achieve a pregnancy and live birth at a much later age. Freezing eggs in advance allows you to store a greater number of better quality eggs than you can at later at a later stage. The eggs do not age while frozen and have been used up to 10 years after freezing.

What are the statistics?

• 8-9 out of 10 mature eggs survive the freezing process (vitrification)
• Around 70% of eggs fertilize
• This will usually result in 1-2 blastocysts.
• Everyone is different but around 20 stored (frozen) mature oocytes is a good number to have a very good chance of a live birth. It should be noted this can take more than one stimulation cycle as not all collected oocytes are mature.
• Freezing at a younger age usually results in better numbers of eggs collected per cycle.

Is there any way of knowing how you will respond?

Initial tests of ovarian reserve with an AMH level (anti-mullerian hormone) and an USS will give a clinician insight into your ovarian reserve, how your ovaries will respond to stimulation and what levels of medication you would require.

What is the process?

Following initial tests it takes about 2 weeks to stimulate the ovaries ready for an egg pick up requiring 1 or two daily medications during this period.

The progress of ovarian stimulation is assessed with blood tests and an ultrasound. At the appropriate time a trigger medication is given. 34-36 hours later you undergo the egg retrieval process. This is an ultrasound guided fine needle egg collection up under sedation. Collected eggs are assessed then frozen and placed in storage. This a short day procedure but you may also require the day afterward off.

When you are ready to try for a pregnancy your eggs are thawed then fertilised with sperm to make an embryo.

Patients undergoing IVF treatment will be given the option for testing embryos prior to transferring them to the uterus.

Preimplantation genetic testing for aneuploidy (PGT-A),

PGT-A, previously known as preimplantation genetic screening (PGS), screens embryos for how many chromosomes they have. The term ‘aneuploid’ describes an abnormal or unbalanced quantity of chromosomes. The term ‘euploid’ describes a normal or balanced quantity of chromosomes. PGT-A involves taking a small sample of cells from an embryo to determine the quantity of chromosomes contained in that sample. The embryo is then frozen while results are pending.

Preimplantation genetic testing for structural rearrangements (PGT-SR)

PGT-SR is a test that can be performed to determine if an embryo has inherited a balanced or unbalanced form of a chromosome structural rearrangement. This screens embryos for their chromosome quantity. Chromosome structural rearrangements are changes from the normal size or arrangement of chromosomes, which are structures that contain all our genetic material. Individuals with structural chromosome rearrangements are at an increased risk of producing embryos or conceptions with extra or missing genetic material, also referred to as unbalanced embryos. Embryos or conceptions with unbalanced chromosomes typically do not lead to successful pregnancy. The aim of PGT-SR is to determine which embryos have balanced chromosomes and selecting for transfer these ‘balanced’ embryos with the highest chance of success.

Preimplantation genetic testing for monogenic/single gene condition (PGT-M),

PGT-M previously known as preimplantation genetic diagnosis (PGD) is an embryo genetic test for individuals who know they are at an increased risk of passing on a known genetic condition. PGT-M can be performed on embryos to greatly reduce the risk of having an affected child. PGT-M involves custom designing a test for each couple and their specific genetic change to identify and select unaffected embryos for transfer. PGT-M is available for individuals who are at increased risk of passing on a specific single- gene condition. You may consider PGT-M if: You and your partner are known carriers of the same recessive genetic condition (for example cystic fibrosis, spinal muscular atrophy, beta thalassaemia) You are a carrier of an X-linked genetic condition (for example Fragile X syndrome, Duchenne Muscular Dystrophy). You or your partner have or are at risk of having a single-gene condition (for example Huntington’s disease, Marfan syndrome) You or your partner have a gene mutation associated with a hereditary cancer syndrome (for example BRCA1, BRCA2, TP53). You or your partner have had a child or pregnancy affected with a single gene condition.