Researchers have perfected a way to allow doctors to screen a single cell from an embryo before the embryo is transferred to the woman's uterus.

As women get older the risk of an embryo containing the wrong number of chromosomes in its cells increases by up to 70-fold. This condition is called aneuploidy.

Chromosomes contain the genetic information, and aneuploid embryos are more likely to fail to implant in the womb, to miscarry or to lead to severe malformations such as Down's sydrome.

Aneuploidy is one of the major reasons behind the lower success rates for assisted conception in women aged over 37.

Italian researchers have now found a way to screen out aneuploid embryos, and to achieve the same pregnancy success rate in women aged 38 to 44 as in their younger patients.

They have achieved this using a technique called FISH (fluorescence in situ hybridization) which enables the analysis of specific genetic information from a single cell.

The technique worked for IVF and for ICSI (intracytoplasmic sperm injection) in which a sperm is injected directly into an egg.

'Age no longer a handicap'

Pregnancy is more likely to fail as women get older

Dr Anna Ferraretti, clinical director of the SISMER Reproductive Unit in Bologna said: "Women planning IVF or ICSI in the final part of their reproductive life can now enter treatment feeling their age is not a handicap any more.

"Pre-implantation genetic screening (PSG) is able to overcome the natural reproductive failure that occurs due to their eggs aging."

Dr Ferraretti, speaking at the European Society of Human Reproduction and Embryology annual meeting in Tours, France, on Monday, said that since September 1996, women over 37 entering SISMER's clinic for several different infertility factors were asked to undergo PGS using the FISH technique to separate embryos carrying chromosomal abnormality from those evaluated as normal.

In total 128 patients aged 38-44 who agreed to undergo PGS of all their IVF-generated embryos had the same pregnancy rate (41%) as 700 younger patients who underwent conventional IVF/ICSI treatment without PGS.

The miscarriage rate in the older women was only four per cent.

In contrast 182 patients aged over 37 who declined PGS achieved only a 25% pregnancy rate and the miscarriage rate was 15%.

The scientists warn that because the FISH technique is limited by using a single embryonic cells, there has been a 5-7% error rate up to now.

Therefore the women were also strongly recommended to undergo conventional prenatal diagnosis to avoid the possibility of an affected baby.

Professor Ian Craft, director of the London Fertility Centre, said the technique would be particularly helpful to women over the age of 40 who suffered a miscarriage rate of one in two when they were helped to conceive artifically using their own eggs.