14 November 2013

Egg freezing: The Facts

Sims IVF logo

Written by

Sims IVF

Sims IVF wants its patients to be fully informed prior to commencing any treatment. There has been recent media coverage regarding egg freezing which has not given the full picture, but the information below looks to add some balance to the current situation.

Open Vs Closed systems; what and why?

  • Vitrification is a method in which samples are cooled ultra-rapidly for long term storage. Due to the special solutions used and the speed of cooling, ice crystals do not form, and instead the samples appear to be in a glass like state. There is existing controversy regarding the risks of using “open systems” for oocyte (egg) or embryo storage following vitrification. In an open system, the samples come into direct contact with the liquid nitrogen in which they are stored. The risk with this method is that either microbial contamination in the liquid nitrogen could affect the samples, or that a contaminated sample could contaminate the liquid nitrogen, which could in turn cross contaminate other samples being stored in the same vessel.
  • With “closed systems”, the samples are completely sealed, normally in specifically designed holding straws which are heat sealed at both ends. In systems such as these, the samples never come into direct contact with the liquid nitrogen and as such the contamination risk is removed. This is by far a safer system and one which all clinics in Ireland and our regulator, the Irish Medicines Board, advocate the use of.
  • Recent media coverage has suggested that these closed systems do not yield comparable results to open systems and that clinics using them are not providing patients with the full information. We do not agree with either of these statements.

1.    Manufacturer’s validation of closed systems

All solutions and equipment used for the vitrification and storage of eggs and embryos have been extensively tested by the manufacturers before coming to market. The solutions and the closed devices for storage have had additional testing to become CE marked and FDA approved. Click here to see a letter from Laura Mena, the Global Product Manager of Irvine Scientific.

2.    Clinical validation of closed systems

· There were some early concerns that closed systems would be less effective than open systems. The fact there is no direct contact between the sample and the liquid nitrogen coolant in a closed system meant that the cooling rate may not be fast enough to prevent damage to the samples. This is a particular risk with oocytes/eggs, due to the large size of the cell. However, studies have taken place over several years to dispel these fears.

· One such recent study was performed by Dr. Dominic Stoop and his team at the Centre for Reproductive Medicine in Brussels, Belgium. Click here to view this peer reviewed paper.

· Dr. Stoop and his team took  a total of 123 donated eggs, vitrified and stored them using a closed system. The 123 eggs were then warmed for 20 recipient women with an average of 6.2 warmed eggs per recipient.

· Of the 123 warmed eggs, 111 (90.2%) survived the vitrification and warming process.

· The 111 surviving eggs then had sperm injected and 86 (77.5%) fertilised normally.

· All 20 recipient women received embryos for transfer and 10/20 (50%) achieved a clinical pregnancy.

· One of the reasons why it is thought that the closed systems are comparable with open systems, is that the warming process (which is considered just as important as the cooling process) is actually open with both methods. With the new techniques in closed systems, the sealed straws are opened whilst the samples are still frozen. The samples are then removed, still without ever coming into direct contact with the liquid nitrogen and then warmed immediately in a dish containing pre-warmed solutions. This is exactly the same process as occurs with an open system, except for the fact that in open systems, the egg/embryo has been exposed directly to the liquid nitrogen and as such has those associated contamination risks. The rapid warming helps maintain the viability and integrity of the cells and leads to excellent results for patients with both methods.

The study by Dr Stoop is only one such study which has proved that storing eggs in a closed system yields excellent survival, fertilisation, embryo development and pregnancy rates. It has also shown that the new closed systems are comparable to the data reported with the older open systems.

Share this