Caerphilly county MPs Wayne David, Chris Evans and Dai Harvard all voted yes in a historic vote to allow the creation of babies from the DNA of three people on February 3.
If passed by The House of Lords, the legislation will mean the first three-person baby could be born next year.
The process, a form of IVF, would be used to help prevent genetic disease where a mother has defective mitochondria that can be passed down to her child.
Mitochondria are compartments in most cells that convert food into useable energy, and if defective can cause brain damage, muscle wasting, heart failure, and blindness.
The law will allow defective mitochondria in cells to be replaced with DNA by a second woman during IVF.
The process will see babies with 0.1% of their DNA from a second mother, but this will not affect characteristics like appearance. Those opposed, claim it could be the start of a slippery slope towards so-called “designer babies”.
But Caerphilly MP Wayne David, said: “There needs to be regulation and we have to be careful with changes to all these kinds of intervention.
“One in 200 babies are born with genes that can cause mitochondria disease and one in 6.500 develop severe risks. If we can prevent that then it’s important to do so.”