The world’s first baby has born from a new procedure that combines the DNA of three people appears to be healthy, according to doctors in the US who oversaw the treatment.

The baby was born on 6 April after his Jordanian parents travelled to Mexico where they were cared for by US fertility specialists.

Doctors led by John Zhang, from the New Hope Fertility Center in New York, decided to attempt the controversial procedure of mitochondrial transfer in the hope that it would give the couple a healthy child.

While many experts welcomed news of the birth, some raised concerns that the doctors had left the US to perform the procedure beyond the reach of any regulatory framework and without publishing details of the treatment.

Speaking to the New Scientist, Zhang said he went to Mexico where “there are no rules” and insisted that doing so was right. “To save lives is the ethical thing to do,” he said.

Mitochondrial transfer was legalised in the UK in 2015 but so far no other country has introduced laws to permit the technique. The treatment is aimed at parents who have a high risk of passing on debilitating and even fatal genetic diseases to their children.

The boy’s mother carries genes for the fatal Leigh syndrome, which harms the developing nervous system. The faults affect the DNA in mitochondria, the tiny battery-like structures that provide cells with energy, and are passed down from mother to child.

Ten years after the couple married, the wife became pregnant but she lost the baby in the first of four miscarriages. The couple had a baby girl in 2005 who died at the age of six, and later, a second child who lived for only eight months. Tests on the wife showed that while she was healthy, about one-quarter of her mitochondria carried the genes for Leigh syndrome.

When the couple approached Zhang for help, he decided to try the mitochondrial transfer procedure. He took the nucleus from one of the woman’s eggs and inserted it into a healthy donor’s egg that had had its own nucleus removed. He then fertilised the egg with the husband’s sperm.

The US team created five embryos but only one developed normally. This was implanted into the mother and the baby was born nine months later.

‘Three-parent’ babies explained: what are the concerns and are they justified?

The baby is not the first child to be born with DNA from three people. In the 1990s, fertility doctors tried to boost the quality of women’s eggs by injecting cytoplasm, the cellular material that contains mitochondria, from healthy donor eggs. The procedure led to several babies being born with DNA from the parents plus the healthy donor. Some of the children developed genetic disorders and the procedure was banned.