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Last Updated: Wednesday, 19 October 2005, 09:54 GMT 10:54 UK
IVF defects higher than expected
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Fertilised eggs can be checked for genetic abnormalities
Many eggs used for IVF carry genetic errors that can cause miscarriage, even those from young women, experts say.

Given the findings of three US studies presented at a fertility meeting in Montreal, some believe all eggs used for IVF should be screened for defects.

UK fertility guidelines recommend such screening only for women over 35 or women who have had repeated miscarriages or failed IVF attempts.

The screening involves testing a single cell from a three-day-old embryo.

Our expert group will monitor the development of this research
A spokesman from the HFEA

Couples at higher than average risk of having offspring with genetic defects are also allowed the screening to check an embryo is free of problems before it is put in the womb to grow.

The screening looks for abnormal numbers of chromosomes, the DNA strands that house genes, and is called preimplantation genetic screening (PGS) for aneuploidy.

It is similar to another IVF (in-vitro fertilisation) check called PGD (preimplantation genetic diagnosis) which looks for specific genes that are known to cause inherited diseases, such as Hungtington's.

The risk of miscarriage and chromosomal abnormalities or aneuploidy increases as a woman ages.

Until now, many had thought eggs from younger women were more likely to be defect-free.

Abnormal chromosomes

However, the three new studies suggest that on average 42% of eggs from all women have serious genetic defects that could prevent embryos surviving to term.

Dr Jeffrey Nelson of the Huntingdon Reproductive Center in California used PGD to screen 289 embryos from 22 healthy egg donors, all of whom were under 30.

Overall, 42% of the embryos had aneuploidy or abnormal chromosomes.

Meanwhile, Dr Peter Nagy and colleagues at Reproductive Biology Associates in Atlanta compared the rate of aneuploidy among younger (under 35) and older (over 38) women.

Nearly two-thirds of the embryos produced by the younger women and three-quarters of the embryos from the older women had chromosomal abnormalities.

A study a the Shady Grove Centre for Preimplantation Genetics in Maryland found eggs from healthy donors aged 21 to 31 had a 52% change of genetic abnormality.

A common problem

Dr Nagy said the findings were a "rewriting" of textbooks.

"These defects should not be present in such a high proportion of patients."

Experts believe it might be that the drugs used for IVF that stimulate a woman's ovaries to produce eggs add to the risk of genetic damage.

It could also be that defective eggs are common among the general population but are rejected early on by the body if they are fertilised.

Doctors already know that many women miscarry very early in pregnancy without ever realising they were pregnant.

Screening IVF embryos before they are placed in the womb is expensive - the technique roughly doubles the overall cost of the therapy.

Dr Nelson believes the UK's Human Fertilisation and Embryology Authority should relax its guidelines and recommend more IVF embryos be screened.

"I think there's an argument that can be made to say they should be more lenient," he told the American Society for Reproductive Medicine meeting.

A spokesman from the HFEA said: "Our expert group will monitor the development of this research and we will listen to the UK's professional bodies if they feel other groups should be added to our general guidance.

"We are concerned that women are properly aware of the potential risks before they choose to have this test and that women and embryos are not tested unnecessarily."

Mr Stuart Lavery, consultant gynaecologist at Hammersmith Hospital and a spokesman for the British Fertility Society, said: "It's very interesting, but it is quite preliminary."

He said Belgian researchers were currently doing a trial to compare the IVF outcomes of young women who receive PGS and those who do not.

He recommended caution about widespread screening because it is still a relatively new technique and is very invasive to the embryo. He said the benefits would have to outweigh any harms.


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