MPs will decide on Tuesday afternoon whether to allow fertility treatments for women with mitochondrial diseases, which would permit the creation of babies with DNA from three different people.
The procedures, which are aimed at stopping the transfer of genetic diseases, will be debated by MPs followed by a free vote. Their decision will then be passed to the House of Lords.
If the vote is passed the UK could be the first country to legalize the creation of children with DNA from three different parents, with three parent children born as early as 2016.
However, the vote has prompted backlash from several institutions, with some senior Catholic Church figures calling for the procedures to be blocked, as one treatment involves the destruction of a fertilized egg.
Most DNA is found in the nucleus of the cell and controls factors such as appearance. However, there are small reserves of DNA found in mitochondria, which, if defective, can pass life-threatening diseases on to embryos.
One in 6,500 babies in the United Kingdom are thought to develop a serious mitochondrial disorder, which can lead to health issues such as heart and liver disease, respiratory problems, blindness and muscular dystrophy.
Problems with mitochondria, the "powerhouse" cells of the body, are inherited from the mother, so the proposed IVF treatment would mean an affected woman could have a baby without passing on mitochondrial disease.
But the cutting-edge IVF technique, which involves transferring nuclear genetic material from a mother's egg or embryo into a donor egg or embryo that's had its nuclear DNA removed, raises ethical questions.
The new embryo will contain nuclear DNA from the intended father and mother, as well as healthy mitochondrial DNA from the donor embryo -- effectively creating a "three-parent" baby.
The amount of donor DNA in the mitochondria will, however, be much less than the parental DNA in the nucleus, which determines the baby's characteristics.