Scientists have announced the first birth of a child born with DNA from three parents. The procedure was developed to prevent a mother from passing to her baby a serious and fatal genetic mutation. This might sound like good news. It is not.

Because the procedure has not been approved in the United States, the U.S. doctor who performed it, John Zhang, did so in Mexico. “There are no rules there,” he said.

Zhang and his team from New Hope Fertility Center in New York City removed the nucleus from both the mother’s egg and a donor egg, inserted the nucleus from the mother’s egg into the donor egg, then artificially inseminated the result and implanted it back into the mother.

The reason this process prevents a mother from passing on a specific genetic mutation is that the mutation does not reside in an egg’s nucleus but in DNA in the mitochondria. The fertility team disposed of the affected mitochondria from the mother’s egg, along with the unused nucleus from the donor egg.