Embryo splitting: a useful procedure in humans?

This week in BioNews, we report on a press conference given by Panos Zavos, a US-based cloning enthusiast, at which he announced that he has transferred a cloned embryo to a woman in the hope of starting a pregnancy. We're always tempted not to run such 'clone claim' stories and, when we do run them, try to be as circumspect as possible about the announcement being made. But with stories splashed across the world's media, it's difficult to ignore.

The media hasn't always taken the same approach. With the niggling feeling that this announcement could just prove to be true, journalists have gone along to the press conferences and reported on the claims. But their patience is running out. Having reported many times on the clone claims of Severino Antinori, Clonaid and now Zavos, the journalists are becoming more and more doubtful that the announcements are anything other than a figment of the would-be cloner's imagination.

This time, there was an added dimension to the announcement. At the same time that he claimed to have performed the first cloned embryo transfer, Zavos and UK fertility specialist, Paul Rainsbury, announced that they are launching an embryo splitting programme for UK couples wishing to travel abroad for treatment. According to press reports, there are two reasons why couples might want to embark upon embryo splitting. The first is to produce more embryos during IVF, thereby increasing the chance of a successful pregnancy. When embryologists are only able to produce one or two viable embryos during an IVF cycle, embryo splitting, say Zavos and Rainsbury, could be used to double the number of embryos available for transfer. The second possible use of embryo splitting is to keep one of the two resulting embryos back, storing it for future therapeutic use. If the baby born of the other embryo falls ill in the future, stem cells could be derived from the other embryo and grown into specialised cells for use in treatment.

Some would argue that embryo splitting as a form of cloning is not as ethically contentious as nuclear transfer. Embryo splitting creates an identical twin and, as such, mimics a natural process. Using nuclear transfer to create a genetic copy of an existing person does not mimic a natural process because it creates identical twins of different ages. There is something in this argument. However, putting the ethical issues aside, the proposed embryo splitting programme, just like its reproductive cloning counterpart, is based on shaky science and there is no clear evidence of benefit to the patients.

Discussing this issue with a number of embryologists, the main response I came across was bemusement. Many cannot see how embryo splitting would help improve IVF success rates, since the main problem facing embryologists is working out which embryos from a batch are most likely to lead to a pregnancy. Further, if an embryo is of poor quality, splitting it in two will just produce two poor quality embryos.

As for putting the extra embryo into storage for stem cell banking, perhaps this could happen in the future. But its value to patients depends firstly upon the embryo splitting not undermining the viability of the embryo that is to be transferred to the womb and, secondly, upon the stem cells themselves being usable for treatment at a later stage. At the moment, without a better understanding of the impact of embryo splitting on human embryos and a much more developed knowledge of embryonic stem cells, it is too soon to be offering such a service to patients.