US 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.

The team 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 “human nuclear transfer” technique was used in China. It is outlawed in many countries, including Britain and the United States.