PGD involves a cell being taken from an embryo at the eight-cell stage; it is done as a screen for genetic disorders and it is a new option for couples at risk of transmitting genetic diseases.

Instead of carrying out a prenatal diagnosis followed by a termination of pregnancy, in vitro fertilisation (IVF) with intracytoplasmic sperm injection (where a sperm is injected directly into an egg) is performed, followed by genetic testing of the embryos and only unaffected embryos are subsequently transferred to the womb.

This latest study from Brussels' Free University has found that screening embryos for genetic disorders incurs no more risk than standard IVF.

The researchers examined the outcomes of 583 children born after pre-implantation genetic diagnosis (PGD) and presented the results at a European Society of Human Genetics meeting.

PGD was first introduced in 1990 as an experimental procedure and there have been considerable concerns over the safety of the procedure because it is new and involves removing a cell from an embryo at around three days old.

Many critics oppose the idea of being able to screen out disorders and concerns have been voiced about the possible genetic risk to children born using assisted reproduction techniques such as IVF because of the manipulation of the egg and sperm during the process.

The process checks fertilised eggs for genetic disorders so that an unaffected embryo can be implanted into the mother's womb, as with conventional IVF.

Around the world researchers have been tracking the progress of PGD babies to monitor the long-term consequences and the Belgian study looked at 563 of the 583 PGD babies which were live births.

These babies were found to have a comparable birth weight to those born after conventional IVF treatment alone, and another fertility procedure called ICSI - where sperm is injected directly into an egg.

At two months, and again at two years of age, the children appeared to be equally healthy and the rate of birth defects or malformations was comparable between the groups.

Lead researcher Professor Ingeborg Liebaers, from the Research Centre for Reproductive Genetics at the Universit?© Libre de Bruxelles, says they were encouraged to find that the major malformation rate was no higher than that which is found in children born after conventional IVF and ICSI.

However Professor Liebaers says the perinatal death rate was higher than in IVF and ICSI babies and this demanded further investigation.

The authors say as most of these deaths were multiple pregnancies, such as twins or triplets, that may be an important factor.

Although experts say they were confident at the outset that PGD would not cause any abnormalities they say they are nevertheless reassured by the results.

But they also say it will take several more decades before the longer-term outcomes are clear as the oldest PGD children are only just approaching 17 years of age.

PGD is a relatively rare procedure, used in less than 200 of the 40,000 cycles of IVF carried out in the UK each year.

Professor Liebaers says they will be carrying out further follow-up as these children grow older.