EMBRYO screening that is used to create “designer babies” does not threaten their health, the largest ever study of the procedure has found.

Babies that have been subjected as embryos to reimplantation genetic diagnosis (PGD) are no more likely to suffer defects at birth than those born of natural pregnancies, according to an analysis of three quarters of all the infants conceived with the help of the technique.

The research, by an American and Italian team, provides the strongest evidence yet that the technique has no significant impact on children’s health.

Experts had feared that the procedure, which involves removing a cell from an embryo at the eight-cell stage and testing it for genetic traits or disorders, might interfere with its later development. The findings support last month’s decision by the fertility watchdog, the Human Fertilisation and Embryology Authority, to lift a ban on using the technology to select embryos purely for their suitability as stem cell donors for sick siblings.

The decision reversed an earlier ruling that the diagnostic technique was acceptable only when doctors were seeking to eliminate a genetic condition, as there was a small theoretical risk of birth defects.

The authority said the conclusions of the latest study were similar to those of unpublished European research that it had considered and which suggested that embryos were placed at minimal risk by the PGD’s biopsy procedure.

“This new study . . . means that all potential parents who use PGD to avoid serious disease can be reassured that the test is not harming their babies,” the authority said.

The diagnostic technique was first developed in 1989 to help couples who carry an inheritable disease to avoid passing it to their children. Embryos are created by IVF, before one cell is removed in order to check its DNA for disorders such as cystic fibrosis. Healthy embryos are selected and transferred to the prospective mother’s womb, while those that carry the genes for the disease are discarded.

The technique is also used to determine whether an embryo is a tissue match for a sibling that needs a transplant, and to detect a kind of chromosomal abnormality called aneuploidy that causes miscarriage.

The new research, led by Yury Verlinsky of the Reproductive Genetics Institute in Chicago, examined 12 years of PGD at the three centres that perform it most often. The Chicago centre, St Barnabas Medical Centre in New Jersey and SISMER in Bologna, Italy account for 754 babies born after the procedure — 75 per cent of all such babies.

The scientists, who published their results in the journal Fertility and Sterility, found that the rate of birth defects was the same as that seen in the general population — about 0.4 per cent for abnormalities such as Down’s syndrome or spina bifida, and between 2 and 4 per cent for minor problems that can be corrected without lasting damage such as cleft palate or hypospadias.

While slightly higher rates of malformation were seen in PGD infants, this was attributable to the age of mothers who typically have the treatment: they tend to be older than the norm.

Maternal age is accepted to be the main risk factor for birth defects.

Some early studies of PGD babies had suggested a higher birth defect rate of between 5 and 6 per cent, but this appears to have been a statistical blip caused by the low numbers of infants examined.

Simon Fishel of the Park Hospital clinic in Nottingham, said: “This is interesting, important and reassuring research. PGD was developed on the back of animal tests showing no evidence of damage, and what we are now seeing, fortunately and with great relief, is that with a very large number of babies born that also applies in humans.”

Mohammed Taranissi of the Assisted Reproduction and Gynaecology Centre in London, said: “It’s always been the case that we have not seen problems with PGD, but it is good to see a large study like this that reflects this experience worldwide.

“Nobody has ever demonstrated that removing a cell from an embryo can cause developmental problems.”

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