06 October 2008
ByAppeared in BioNews 478
Nataly Atalla's uncritical advertorial 'freeze and share: an evolution of egg sharing' in BioNews 476 (week 15/9/2008 - 21/9/2008) did not address a number of important points.
I would have expected some comment on the success rate of the vitrification technique in their hands. She cites 100,000 procedures in 12 countries and 95 per cent survival and 96 per cent fertilisation rates being reported, but makes no mention of live delivery rates and in particular no reference to the results at her own unit, the London Bridge Fertility Gynaecology and Genetics Centre (the Bridge Centre). Results presented at the recent European Society of Human Reproduction and Embryology (ESHRE) meeting in Barcelona were very encouraging. Chang et al in Atlanta, Georgia, US, vitrified and warmed 155 mature donated oocytes, 135 survived and 117 fertilised with ICSI. They transferred 52 blastocysts into 20 recipients and detected 29 fetal hearts in 17 recipients (1).
However, great care needs to be taken when comparing results elsewhere with those in the UK. In the US, success rates per fresh cycle of egg donation treatment are commonly quoted as being over 60 per cent, whereas the Bridge Centre's most recent published results (HFEA (Human Fertilisation and Embryology Authority) 2007 clinical pregnancy data) was 27 per cent (9/34). This discrepancy is probably due to the age of the donors - 23 year-old eggs can always be expected to do better than 33 year-old eggs. The vitrification technique may prove to be better than slow freezing but cryopreservation followed by IVF and embryo transfer cannot be expected to give better results than those achieved with fresh embryos.
Further, slow freezing results vary from clinic to clinic and the same is likely to be the case with vitrification. Vitrification is more demanding in the laboratory than freezing because precisely controlled exposure to the vitrification solution before cooling and the subsequent rate of warming are critical for survival (2). In the 'freeze and share' scheme, vulnerable women as they approach their mid-30s are being encouraged to put their faith in a storage technique with as yet unproven efficacy in the hands of a clinic offering to exchange storage for eggs to donate to other women. These women may then delay childbearing, become infertile, not conceive with their own stored eggs and know that a woman or women conceived with the fresh eggs they donated some years previously.
How many eggs should the donor store to give herself a 'reasonable' chance of success should she find she needs to use them? Motta et al in Sao Paulo, Brazil and Michigan, US, using excess eggs vitrified and stored and subsequently, if the woman did not conceive following fresh embryo transfer, warmed and ICSI'd, achieved a clinical pregnancy rate of 38 per cent (3). Although the eggs they used were provided by women with a fertility problem this result is much more like what we could expect in the UK. They estimated that 17 cryopreserved oocytes (eggs) were required to establish a single clinical pregnancy. At the Bridge Centre suitable donors will undergo three treatment cycles in a year. If they are to store that number of eggs they will need, in order to give half to the recipient, to produce 34 mature eggs, say a total of 40 eggs from about 50 - 60 follicles. It can be seen that this will require a degree of overstimulation with the risks that that would incur.
What proportion of women storing their eggs will need them later? Atalla's commentary makes it clear that only women who are likely to respond to relatively low doses of fertility drugs will qualify to be donors. These women are less likely than those not suitable to donate to have difficulty conceiving in their late thirties and early forties. It appears therefore that the women who are least likely to need the eggs are storing their eggs - perhaps the idea is that they will donate these eggs to the women who were not suitable to donate and store their eggs? A win / win situation for the clinic?