How does the technique work?
The procedure involves removing the genetic information from an affected mother's fertilised embryo before inserting it into one from a healthy female donor, from which the genetic information has been removed.
Crucially, the hundreds of thousands of diseased mitochondria are left behind, leaving the new embryo with healthy ones present in the donor embryo.
Mitochondria contain a tiny amount of their own unique genetic code, so the resulting babies carry DNA from three different people.
But because it represents just 0.02% of our total DNA and has no bearing on genetic traits we inherit from our parents, researchers behind the technique, have never liked the "three-parent" moniker.
However, the technique - whatever you choose to call it - isn't perfect.
A total of 22 women underwent the procedure but only seven became pregnant, resulting in eight births - a 36% success rate.
Five of the eight babies were born with no trace of disease.
But tests on the other three revealed a small percentage of mutated mitochondria had been carried over during the procedure.