British scientists have received official permission to genetically modify human embryos.
The Francis Crick Institute in London could begin experiments within weeks after the Human Fertilisation and Embryology Authority (HFEA) approval yesterday.
The scientists want to deactivate genes in leftover embryos in IVF clinics to see if it hinders development.
It will be only the second time worldwide such a procedure has been undertaken and the first time it has been directly approved by a regulator. A Chinese team was widely criticised last year for similar experiments.
About 50 per cent of fertilised eggs do not develop properly and experts believe a faulty genetic code could be responsible.
If scientists knew which genes were crucial for healthy cell division they could screen out embryos with flawed DNA, potentially preventing miscarriages. The initial pilot, which will also have to pass an ethics evaluation, will involve up to 30 embryos and the team would like to work on a further three genes, which could bring the total number of embryos used to 120.
Critics say the plan opens the door to designer babies and genetically modified humans. But lead scientist Dr Kathy Niakan said the research could fundamentally change our understanding of human biology and give hope to prospective parents.
"We would really like to understand the genes that are needed for an embryo to develop into a healthy baby," she said. "Miscarriage and infertility are extremely common but they are not very well understood."
The team is already in talks with fertility clinics to use their spare embryos.
It is not illegal to edit human embryos for research purposes although it has never been done.
An HFEA spokesman said it had stipulated no research using gene editing might take place until the research had received research ethics approval.
The aim of the new project is to find out what causes the cells to turn into different kinds, a process known as "lineage specification".