THE first trial of a controversial fertility treatment that would effectively create babies with three genetic parents has ended in the miscarriage of twins.

A 30-year-old Chinese woman who had undergone the therapy, which was designed to “refresh” her fertilised eggs by merging them with those of a donor, has lost all three of the embryos that she conceived: one was aborted, and two miscarried six months into her pregnancy.

Despite the experiment’s unfortunate outcome, scientists behind it hailed it as an important advance that eventually could help thousands of infertile couples to conceive their own genetic children. None of the foetuses was lost as a result of the therapy and genetic tests on the two that miscarried have shown them to be normal.

The fact that the pregnancy progressed normally for 24 weeks suggests that the technique is viable, and will be useful for treating infertility and genetic disease, they said.

The work has raised serious ethical concerns because of its similarity to cloning and because it involves “germline” genetic engineering — the introduction of traits that can be passed down the generations. As a result, it is unlikely to be repeated soon. Such research is outlawed in most countries, including Britain. Even China, which permitted the trial after it was blocked in the United States, is expected to ban any further human experiments.

The controversial procedure, which was originally developed at New York University and tested at Sun Yat-Sen University in Guangzhou, is designed to help women who are sterile because their eggs do not develop properly when fertilised.

Details of the pregnancy will be presented today at the American Society of Reproductive Medicine conference in San Antonio, Texas, by Jamie Grifo and John Zhang, of New York University, who developed the technique. The operations were performed by their Chinese colleagues.

Dr Grifo said that while the result had been “very unfortunate”, the experiment had revealed the technique to be workable. “The pregnancy failure was due to the obstetric complications of a multiple preganancy,” he said. “The bottom line is that the foetuses were normal.”

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