Live birth rates following IVF using previously frozen eggs are lower than when fresh eggs are used, at around 2-3 per cent per egg, said Professor Adam Balen, Chair of the BFS Policy and Practice Committee. 'It is essential for more research to be carried out in this area to develop the techniques used and improve the safety and efficiency of egg freezing,' he said. The BFS and ACE say that patients currently have a greater chance of a successful pregnancy if they decide to store an embryorather than their eggs, if possible.
Egg freezing allows women to store their eggs for future use when they are 'thawed' and fertilised. The technique involves removing eggs from the woman's ovaries following ovarian stimulation and stored in liquid nitrogen. The BFS and ACE say there are two main techniques: slow cooling, which uses a lower concentration of chemicals to protect the eggs from potential damage during the freezing process, and vitrification, where eggs are frozen more quickly but uses a higher concentration of chemicals. Early studies indicate that vitrification produces higher success rates. The guidelines also recommend using mature eggs for best fertilisation rates and to also fertilise thawed eggs using ICSI (intracytoplasmic sperm injection), a procedure where sperm is injected directly into one egg.
However, there are safety concerns that still need to be explored. Risks to patients include ovarian hyperstimulation syndrome (OHSS) and an increased likelihood of chromosomal defects in the eggs. There are also safety concerns with extracting a 'large' number of eggs to increase the changes of producing a viable embryo at a later date. Due to the lack of available data on the health affects on children born using frozen eggs, many commentators are calling for a cautious approach. The guidelines followed a review of the various techniques used in egg freezing and generally concluded that further research was necessary to properly identify both the risks and improve success rates. 'The British Fertility Society wants to ensure that all women receive the safest and most effective treatment when undergoing fertility procedures,' said Professor Balen. Mrs Rachel Cutting, from ACE and who co-authored the guidelines said that 'egg freezing is a relatively new treatment which offers promising initial results. Although research in this area has moved forward considerably in the last few years, we still need to know more.'
Both the BFS and ACE say they support egg freezing for medical purposes, such as where women become infertile following surgery or cancer treatment, but not as a solution to enable women to counteract naturally declining fertility and choosing to undergo IVF in later life. The guidelines will be next reviewed in 2013.