The embryos contained nuclear DNA from one mother, and mitrochondrial DNA from another. Credit: ©

Doctors have created the first pregnancies using a controversial technique related to cloning. The babies died before birth.

Other experts have condemned the procedure because the health risks are unknown. "You'd find it hard to find people that support it," says reproductive-medicine researcher Chris Barratt of the University of Birmingham, UK.

James Grifo of New York University School of Medicine developed the technique, while colleagues at Sun Yat-Sen University of Medical Science in Guangzhou, China created the human embryos1. The results are presented today at the American Society for Reproductive Medicine's annual meeting in San Antonio, Texas.

The team in China fertilized eggs from two women in test tubes. They then sucked out the nucleus of one egg and injected it into the other, which they had stripped of its own nucleus. The idea is that the second egg will better direct the growth of an embryo.

The team implanted five embryos into a 30-year-old mother who had already undergone two failed attempts at in vitro fertilization (IVF). Three embryos grew large enough for doctors to hear their heartbeats.

After a month, doctors reduced the pregnancy to two for the mother's safety, but one fetus died at 24 weeks and the other by 29 weeks. Whether the process was responsible for their deaths is not known.

The technique - called human nuclear transfer - is outlawed in some countries such as the UK. "It's extraordinary. You wouldn't get away with it anywhere else," says IVF doctor Allan Templeton of the University of Aberdeen, UK.

Templeton argues that there was no compelling reason for using the technique on the woman, because further rounds of IVF might have worked. "The clinical justification is extremely dubious," he says.

The team say that they hope to help women whose own eggs are unable to undergo successful IVF, or who carry damaging mutations in their mitochondrial DNA.

Close to cloning

The new method comes close to human reproductive cloning, which is banned in many countries. In cloning, the nucleus of an adult cell, rather than of a fertilized egg, is injected into another egg so that the embryo is genetically identical to its parent. Grifo's technique creates embryos with genes from both mother and father.

Like cloning, critics warn, Grifo's method might damage or incorrectly programme the mother's DNA. What's more, the embryos carry genetic material from two mothers: nuclear DNA from one, and small packages of DNA in the mitochondria from the other.

The clinical justification is extremely dubious Allan Templeton , University of Aberdeen

The effect of inheriting DNA from two mothers is unknown. Proteins made from the two sets of genes may be incompatible, perhaps even stopping the embryo's cells working.

A handful of children have been born through a related technique, in which one woman's eggs are pepped up by injections of the cell cytoplasm and mitochondria from another, fertile woman's eggs. This technique is also now outlawed in some countries.