Scientists have called on the British Government to give its immediate approval to laws allowing three-parent babies after experts found the techniques were safe.
The Human Fertilisation and Embryology Authority said it had examined a "voluminous" amount of data and concluded the techniques were not "unsafe" and were "potentially useful". But it said further experiments, including on human embryos, were needed.
The procedure sees donor DNA from a "second mother" implanted into a defective egg to prevent children suffering from inherited genetic conditions such as muscular dystrophy.
Supporters say the technique would allow affected couples the chance to have their own, genetically-related healthy offspring, but critics have warned it could lead to "designer children".
The Government began a consultation on draft regulations in February, asking a panel from the HFEA to examine the safety and effectiveness of two techniques.