Two advances in pre-implantation testing of in vitro fertilization (IVF) embryos offer advantages for higher pregnancy rates and more desired genetic features in offspring. First off, at least for some categories of women having reproductive problems a new embryo screening technique called comparative genomic hybridization (CGH) can double the rate of successful pregnancies when using IVF.
The new approach improves on this by testing IVF embryos when they reach the blastocyst stage of 100 to 150 cells. This allows extra cells to be removed for genetic analysis, giving increased accuracy.
It also employs a more advanced profiling system called comparative genomic hybridisation, which can screen all 23 pairs of chromosomes, against only ten with existing techniques.
The technique involves letting the embryos divide more times before cells are extracted for testing. Unlike in previous techniques all 23 chromosomes are tested for aneuploidy (where the wrong number of chromosomes is present rather than a pair of each chromosome type).
In the new approach the test is conducted on blastocysts, embryos grown for five days until they have 100 to 150 cells. These are larger and stronger, allowing cells to be removed more safely
So more cells are removed later and then fancier tests are done on them.
Oxford Fertility Unit has applied for a licence that would allow them to carry out sophisticated screening of embryos to look for defects which reduce the chances of them leading to a successful pregnancy.
Current techniques mean that only half of the embryo's DNA can be checked for problems before being implanted in the womb.
A new method, which is being used in America, can check 23 pairs of chromosomes, meaning many more defects can be found and those embryos discarded so only the perfect ones – with the best chance of creating a baby – are then implanted in the womb.
Analysing the embryos using the latest technique meant that all 23 had at least one normal blastocyst for transfer. A total of 50 embryos were transferred in 23 cycles.
Of the women, 21 fell pregnant (91%) and 20 (87%) had a clinical pregnancy (where a foetal heartbeat is confirmed by ultrasound).
Experts predict the live birth rate will be 78%. This compares with an anticipated 60% for the same patients without embryo screening.
Research team members Dr Mandy Katz-Jaffe at the Colorado Centre for Reproductive Medicine and Dr Dagan Wells of Oxford both think this testing technique works much better.
"The pregnancy rates we've got so far are absolutely phenomenal," said Dr Dagan Wells at Oxford University and Reprogenetics UK, who led the study. "We're ready to begin a trial in the UK, and we have a couple of licence applications in to the Human Fertilisation and Embryology Authority to start offering CGH to patients." The HFEA is the UK's regulator of fertility clinics.
Another advance in embryo genetic testing will have greater impact in the long run: Karyomapping allows checking of all known genetic conditions.
“What we’re basically doing is mapping family trees, so you can work out which parts of your chromosomes came from which grandparents,” Professor Handyside said. “This turns out to provide a truly universal method for PGD – that’s why we’re excited about it.
“At the moment, there are preimplantation tests for only a small fraction of the 15,000 genetic conditions that are known. This test is capable of detecting any of them. There is no need to find the mutation that is affecting a family, and work up a test. You do the analysis, and just read off the results.”
As the technique maps all the embryo’s chromosomes, it can check any gene, allowing several to be screened at once. It could also be used retrospectively, once an embryo has become a child, to provide wider information about its genetic inheritance.
With declining costs for genetic testing just about any genetic variation that has functional significance will be testable before embryos are implanted. Combine that testing ability with understandings of what more genetic variations mean and very suddenly we are going to reach a stage where embryo selection offers huge advantages to anyone who wants to make their offspring smarter, better looking, healthier, or possessing of any other most desired genetic features of each parent.
Once we know the meaning of enough different genetic variants the use of natural sexual relations to start pregnancies will pass out of favor for large segments of many populations. In nations where governments allow people to select embryos for reasons other than disease avoidance (and I expect the US to fall into this category) the advantages for couples who want smarter kids, kids with desired personality characteristics, kids with better looks, and other qualities will be so incredibly compelling that IVF with genetic testing will become very common very quickly. I expect it to take off first with the most educated and most affluent and ambitious.
By the year 2020 I predict at least 10% of all pregnancies in the United States will involve IVF and embryo genetic testing. Governments that restrict this testing are setting up their populations to fall behind in intelligence and other measures.
|Share |||Randall Parker, 2008 November 09 07:13 PM Biotech Reproduction|