For the first time in the UK, a baby was born using three people's DNA, according to the fertility regulator.
The majority of the DNA comes from the baby’s two parents, with only 0.1% coming from a third, donor woman, reports BBC.
The ground-breaking technology aims to prevent infants from being born with catastrophic mitochondrial disorders.
There have been less than five such births, but no additional information has been given, the BBC report said.
Mitochondrial disorders are deadly and can occur within days or even hours of birth. Some families have lost several children, and this procedure is viewed as their sole hope of having a healthy child of their own.
Mitochondria are small compartments found within almost every cell that turn food into usable energy.
Defective mitochondria fail to provide energy to the body, resulting in brain damage, muscle atrophy, heart failure, and blindness, the report added.
They are only passed on by the mother. So mitochondrial donation therapy is a modified kind of IVF in which mitochondria from a healthy donor egg are used.
This donor DNA is solely important for producing functional mitochondria; it has no influence on other features like appearance, therefore thus does not constitute a "third parent."
The procedure was pioneered in Newcastle, and in 2015, rules were passed in the United Kingdom to allow the development of such newborns, it said.
However, the UK did not proceed immediately. In 2016, the first baby delivered using this procedure was to a Jordanian family receiving treatment in the United States.
Prof Robin Lovell-Badge, from the Francis Crick Research Institute, said: "It will be interesting to know how well the mitochondrial replacement therapy technique worked at a practical level, whether the babies are free of mitochondrial disease, and whether there is any risk of them developing problems later in life."