Tuesday October 18 2011
The tool tests for abnormalities in IVF embryos
“Three-in-one test that ‘virtually guarantees IVF success’ could be available within months,” reported the Daily Mail. It said that the test allowed only the best eggs or embryos to be selected for IVF, and is expected to “slash the odds of miscarriage and greatly boost the chances of a woman having a healthy baby”.
The research was presented at the American Society for Reproductive Medicine’s annual conference and only limited information is currently available. What is known is that this new technique simultaneously examines various aspects of embryo or egg DNA associated with a lower chance of a successful pregnancy. The researchers found they were able to measure sequences of DNA and check that the cells had an appropriate number of chromosomes with similar accuracy to existing tests that measure these separately.
While promising, this technique has not yet been tested in a clinical trial and its effectiveness at improving IVF success rates still needs to be established. Until a detailed write-up of this research is peer reviewed and published, it is difficult to comment on how robust these findings appear to be.
It is also important to emphasise that there are other factors that contribute to miscarriage or unsuccessful IVF, such as the health of the mother and abnormalities during pregnancy, which would not be detected using this test. Although this research may be promising, it does not yet offer a full guarantee of IVF success as some newspapers have suggested.
Where did the story come from?
The study was carried out by researchers from the University of Oxford and was presented at the American Society for Reproductive Medicine’s annual conference in Orlando in mid-October.
This is promising research but several newspapers have overstated the implications of its findings and suggested that the test could produce a 100% success rate for IVF. To date, the researchers have only compared the accuracy of this test against other tests to measure various aspects of embryo DNA. A clinical trial would need to be carried out to measure the test's effectiveness. It is also not clear whether the test would lead to more pregnancies or healthier babies than other established methods.
What kind of research was this?
This was laboratory research in which scientists developed a method to test for common abnormalities in embryos that have been produced through IVF that make them less likely to implant and develop into a healthy foetus in the womb.
In the UK, only one or two embryos are implanted in each IVF cycle to avoid the risks of multiple pregnancies. The researchers say that in order to maximise IVF success rates, it is essential the embryo most likely to produce a healthy birth is identified and prioritised for transfer into the mother’s womb. They add that improvements could be made on existing techniques to improve the chances of successful and healthy pregnancies.
This research has been presented at the American Society for Reproductive Medicine’s annual conference and an abstract containing limited information on the research is available. However, it will only be possible to get a better idea of how robust these findings are when the study has been written-up as a research paper and gone through the peer review process.
What did the research involve?
The researchers made a ‘microarray’, which is a small, solid surface onto which thousands of tiny spots of different sections of DNA are placed. This technique is commonly used to allow scientists to measure the activity of many genes at the same time.
The microarray the researchers created enabled them to examine whether the DNA contained particular sequences (or abnormalities) and to detect features of chromosomes - the structures that contain DNA in the cell. They could also see how many mitochondria - the powerhouses of cells - the embryos contained.
The researchers tested three different types of sample:
- polar bodies: which are found in egg cells and are bi-products of the type of cell division that makes an egg cell
- blastomeres: a type of cell produced by division of the egg after fertilisation and during early embryonic development
- trophectoderm biopsy: which takes a sample of the outer cells of the embryo, five to six days after fertilisation when it is called a blastocyst
The researchers tested 37 polar bodies, 64 blastomeres and 16 trophectoderm biopsies. They were interested in whether the cells had the correct number of chromosomes and whether the chromosomes had long telomeres (sections of DNA at the end of chromosomes that protect the chromosomes as the cell divides). They were also interested in the quantity of mitochondria (which would have come from the mother originally).
The microarray was compared with two types of established genetic techniques: one that determined whether the cell has the correct number of chromosomes, and another that looked for the length of telomere DNA and the amount of DNA from mitochondria.
What were the basic results?
The researchers were able to detect 226 of the 240 instances where there were incorrect numbers of chromosomes (94% sensitivity) meaning that in 14 instances abnormal chromosome number was not detected. The quantification of the size of the telomeres and the mitochondria DNA was 100% in agreement with the established genetic techniques that measure these.
The researchers looked at factors that were associated with cells having an abnormal number of chromosomes. They found that polar body and blastocyst samples that had the wrong number of chromosomes also had chromosomes with shorter telomeres. They found in the blastomere samples that there were fewer mitochondria in the samples that had the incorrect number of chromosomes than those with the correct number.
How did the researchers interpret the results?
The researchers say that this is an easy to use tool for the simultaneous analysis of multiple aspects of egg cell and embryo biology. They say that quantification of mitochondria and telomere DNA may be of clinical relevance and may allow healthy egg cells or embryos to be developed further so that they can be transferred to the womb.
They also highlight the potential use of this tool for research, in that it would allow researchers to look at different aspects of embryo cell development at the same time.
This conference abstract describes a tool that can look at different aspects of the ‘quality’ of egg and embryo cells at the same time, rather than having to use separate tests to measure them separately. Preliminary research on a small sample suggests that this technique produces similar results to analysing these features separately.
These appear to be promising findings but it is important to emphasise that this research has been presented as a conference abstract, and that there is only limited information available at present. Further details of how this research was carried out and its results should be available when it is published. It will also have to go through the peer review process, during which it is assessed by other experts in fertility on how robust the science is.
There are several steps that would need to take place for this screening test to be approved for use in the UK. Firstly, the conditions that should be tested for would have to be assessed as would whether this type of screening is ethically acceptable by the regulatory body that regulates IVF in the UK, the Human Fertilisation Embryology Authority.
Furthermore, a clinical trial is necessary to ensure this technique was safe. It is also necessary to determine the extent to which screening with this test results in successful pregnancies and healthy babies when compared to existing techniques that select which embryos to transfer into the womb.