The subject of "three-parent children" was raised last week when reports said a woman had given birth to a baby in Greece using genetic material from two women and a man.
A medical team from Barcelona used a technique on the 32-year-old Greek woman called maternal spindle transfer (MST), reportedly to overcome fertility issues she was experiencing.
Here's the key information you need to know about the technique:
How does it work?
"All cells have mitochondria, which are like power packs for the cells and create the energy that keeps cells alive," Tim Child, Associate Professor at the University of Oxford and Medical Director of Oxford Fertility, told Euronews.
While a child's DNA is a mixture from both the mother and father, mitochondria are separate "packages of genetics" that come solely from the mother.
Some people have a mitochondrial disease — a problem with the genetics in their mitochondria — which can lead to severe, life-threatening conditions, although this is rare.
One treatment for a woman who might have one of these diseases is to replace the mitochondria in her eggs via IVF.
This can be done via a process like the one used in Greece where the DNA is taken out of the woman's egg and put into a donor woman's egg once the DNA has been stripped from it, which is then fertilised with sperm to create an embryo.
Why do it?
The only current licenced reason to carry out the procedure in the UK is for women with mitochondrial disease.
The decision was made after public consultation and after the issue was debated in Parliament.
It is closely regulated and anyone wanting to do it has to apply for a special licence, but this is not the case across Europe as the clinical trial in Greece showed.
However, in the 1990s, trials took place in Britain with couples that were having difficulty conceiving but where the women did not show signs of a mitochondrial disease — the mitochondria from a donor was injected into the woman's egg.
"It was believed this could help IVF success rates, but this was very questionable and no one definitely believed that it worked, or not," Child explained.
This is what the scientists in Greece have done, for a couple that has had four failed IVF cycles, but there is no evidence that doing this helped them, he added.
Even though this patient had four failed IVF cycles, sometimes cycles work on the fifth try, so it is impossible to tell if the woman would have had a baby if she tried again with her own eggs.
"Maybe if she had eaten a tube of smarties, she would have had a baby — does that mean eating the smarties led to the baby? It doesn't," Child said.
What are the risks and ethical issues associated with the technique?
Child argues that it is hard to get a full picture of the risks as this is an "untried technique" — one that has rarely been carried out.
In the trial in Greece, 99.9% of the DNA in the egg was from the mother and 0.1% from the donor, which combined would then make up 50% of the embryo's DNA.
While this is a very small percentage of the child's DNA and won't affect characteristics like hight or hair colour, it will still be passed on to generations to come.
"We don't know for sure if that's an OK thing to do, we just don't know," said Child. "The safety side of this hasn't been established
"If you're doing this because you're trying to prevent mitochondrial disease, which is a horrible disease, you might think this is a small, unknown risk but if you're doing and you don't know if it should be done in the first place, that's quite a different scenario."
His stance on using the technique for women who don't present a mitochondrial disease is clear: "It shouldn't be done. Particularly in an unregulated way with no proper scientific oversight."
For free, clear and impartial information for all affected by fertility treatment, you can look on the HFEA's website.