But how exactly does a baby end up with three "parents," and why is the technique so controversial?
The babies that result from this technique can only attribute around .1% of their DNA to the third party, so "parent" is a bit of a strong word. The donor provides only their mitochondria. Often called the "power plants" of the cell, the mitochondria converts energy from food into energy that can power a cell. When someone's mitochondria don't function properly, it's bad news indeed.
Mitochondrial diseases can cause a whole host of life threatening problems, and it's estimated that as many as 4,000 children are born with such conditions in the United States each year.
The technique up for vote, which was developed by British researchers, takes a mitochondria from a healthy female donor and combines it with the DNA of two parents in an in-vitro fertilization. This can be accomplished at either the egg stage or the embryo stage: In one method, two eggs are fertilized with the father's sperm -- one from the donor, and one from the mother -- and the parents' genetic information is inserted into the donor's embryo, which has had everything but the mitochondria cleared out. In another, the nucleus of a mother's egg cell is placed directly into a donor egg, replacing the original nucleus there.
Last week, 40 experts from 14 different countries signed a letter to The Guardian urging British politicians to support the donation protocol. But the Church of England has come out in opposition of the technique. Naysayers cite ethical concerns: Some take a pro-life stance, arguing against the embryo destruction that occurs during the process. Others have expressed concern that this technique opens the door to "designer babies" chosen for desirable physical or mental traits.
"The biggest problem is that this has been described as three-parent IVF. In fact it is 2.001-parent IVF," Gillian Lockwood, a reproductive ethicist, told the BBC. "Less than a tenth of one per cent of the genome is actually going to be affected. It is not part of what makes us genetically who we are.It doesn't affect height, eye color, intelligence, musicality. It simply allows the batteries to work properly."
There are already people out three with 2.001 parents. A similar technique was pioneered in the U.S. during the 90s, but was banned after less than 100 babies were born.
In fact, having a stranger's DNA in your body permanently isn't a novel idea at all.
"Think about bone marrow transplants,"Peter Braude, emeritus professor of obstetrics and gynecology at Kings College London, told the BBC. "Let's say unfortunately you have leukaemia and you have to have your bone marrow radiated for the cancer to be killed and then it is replaced by bone marrow from someone else - say me. Effectively from that time onwards, you will have circulating in your body DNA from me. You won't be related to me, you may be grateful to me, but you will have DNA from a third person circulating in your body."
This post has been updated.