Wednesday, November 12, 2008

Frozen IVF embryos produce healthier children

That does NOT mean that the method is safer. It's just natural selection at work: Only the most robust survive freezing

IVF produces healthier children when embryos are frozen and thawed before being transferred to the womb, according to new research. Babies born from frozen IVF embryos are less likely to be born prematurely or underweight than are those conceived during fresh treatment cycles, three independent teams of scientists have found. One of the studies also recorded lower rates of stillbirth and early death among frozen-embryo babies. The results, from researchers based in the United States, Australia and Finland, suggest that far from being riskier than conventional IVF, as is generally thought, cycles using frozen embryos may actually be safer.

The research is particularly significant because separate teams from three countries have reached the same conclusion, each using large samples including thousands of IVF cycles. A fourth team, from Denmark, also reported similar findings earlier in the year.

Scientists said the work would be important because women are increasingly encouraged to use just one fresh embryo during IVF, to guard against damaging twin and triplet births, and to freeze any that are left over for later use. It will dispel doubts about whether this policy trades the risks of multiple births for hazards associated with frozen embryos. Allan Pacey, secretary of the British Fertility Society, said: “This all works to the advantage of single embryo transfer. It suggests it might be better from the point of view of a healthy child to go for frozen embryos, which is an integral part of the strategy. People shouldn’t be scared of frozen embryos.”

The studies, presented at the American Society for Reproductive Medicine conference in San Francisco, do not explain why babies born from frozen embryos seem to do better, but there are several hypotheses. When fresh embryos are used in treatment, women may still be under the influence of powerful hormonal drugs used to stimulate their ovaries into producing extra eggs, or the anaesthetics used during egg collection. Either of these may interfere with the endometrial lining of the womb, and thus with the formation of the placenta.

Another possibility is that as some frozen embryos generally fail to survive thawing, this effectively “weeds out” those that are of poor quality. A third possibility is that women who produce lots of good quality embryos are more likely to have frozen cycles, and also have a lower risk of complicated pregnancies.

“These findings are really quite interesting,” Dr Pacey said. “It kind of defies logic to a certain extent. It seems to be an issue with the formation of the placenta, but how it has an effect isn’t known. “This may be a bit of biology that has escaped most people. The assumption has always been that if the endometrium [the womb lining] is thick, it’s functional. In an IVF cycle, the endometrium looks normal on ultrasound, but perhaps there is something subtle going on.”

Despite their apparent health benefits, however, frozen IVF cycles are unlikely to supplant fresh ones as the routine option because they have a lower success rate. In Britain, 24.4 per cent of fresh cycles lead to a live birth, compared to 17.4 per cent of frozen cycles. There were 33,916 fresh cycles performed in 2006, and 7,911 frozen cycles.

More here

Embryo `quality check' could double IVF success rate

Infertile couples could double their chances of starting a family by IVF, with an embryo quality test developed by British and American scientists. The first trial of the procedure, which identifies embryos with the best chances of developing into healthy babies, delivered remarkable results that suggest it could transform IVF success rates, while helping to prevent damaging multiple pregnancies. Of 23 women to have their embryos genetically screened with the technology, two have given birth while another 16 are currently pregnant and have passed the point at which miscarriages typically occur. Another two became pregnant but miscarried. The 78 per cent success rate is particularly outstanding because all the patients had a poor prognosis, with an average age of 37® and a history of failed attempts at IVF or miscarriage.

Dagan Wells, of the University of Oxford, who leads the research team, has applied for permission from the Human Fertilisation and Embryology Authority (HFEA) to offer the test at the Oxford Fertility Unit, and a British trial is expected to begin next year. The test will eventually cost about 2,000 pounds.

It could raise success rates when only a single embryo is used. The HFEA has launched a strategy to promote single embryo transfer, to guard against twin and triplet pregnancies - the biggest health risk of IVF. Dr Wells said: "The pregnancy rates we've got so far are absolutely phenomenal." The probability that one embryo leads to a pregnancy is doubled, he said. "That means that you've got a much better chance of a pregnancy if you do a single embryo transfer."

The new procedure to detect chromosomal defects called aneuploidies was developed by Dr Wells with colleagues from the Colorado Centre for Reproductive Medicine near Denver. More than half of all embryos are aneuploid, which means they have too many chromosomes or too few. Most of these fail to implant in the womb or miscarry, while the few that survive have chromosomal disorders such as Down's syndrome. While a preimplantation genetic test for aneuploidy is already available, it is controversial as there is little evidence that it helps women to conceive. Some studies have even suggested it is harmful, and the British Fertility Society recommends that it should be offered only in clinical trials.

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.

In the trial, which will be presented today at the American Society for Reproductive Medicine conference in San Francisco, patients had IVF at the Colorado centre, and cells were then removed and DNA sent to Oxford for analysis. Once the normal embryos had been identified, these were then implanted. The 78 per cent success rate recorded so far is significantly better than the 60 per cent that the clinic usually achieves for this patient group. For each individual embryo, the implantation rate is 62 per cent, against a normal rate of 28 per cent.

Mandy Katz-Jaffe, of the Colorado centre, said: "This is still a trial, and we don't offer it yet as a clinical procedure. But this is very promising." Allan Pacey, of the British Fertility Society, said the results were interesting, but that it would need to see larger studies with a control group before the society changed its policy on preimplantation screening.


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