During their meeting on 15th December, The Human Fertilisation and Embryology Authority (HFEA), which regulates fertility matters in the UK, has endorsed the findings of a scientific review concluding that Mitochondrial Replacement Therapy should be approved for “cautious clinical use”.

This has been widely reported as allowing for the creation of “three parent babies”. Legally, that is not true. The child born with the assistance of the therapy will have two legally recognised parents – the couple who worked with their doctors to have a family together.

Why might that be? Looking at the science behind the therapy, it becomes clear that third party (“the donor”) has minimal involvement.

What is Mitochondrial Replacement Therapy?

Mitochondrial Replacement Therapy becomes an option when a woman is unable to have a healthy child because her mitochondria (the structures in the cell which produce the chemical energy the cell needs) are damaged. Mitochondrial diseases vary in severity, but more severe forms may cause children to die very young or miscarriages.

Unlike most other parts of the cell, mitochondria contain their own genetic material and so can be replaced without interfering with other genetic material in the cell. Mitochondrial Replacement Therapy uses a donor cell to replace the mother’s mitochondria with those of the donor.

How Much Involvement Does the "Third Parent" Have?

Either way, the child will have ALL of their nuclear DNA (the genetic material which is responsible for appearance and, probably to some extent, personality) from their parents. They will have their mitochondria from the donor. The embryo so created will then be implanted into the mother, who will go through the pregnancy and give birth to the baby. This means that (except for the mitochondria) the genetic mother and the birth mother will be the same person.

That person will be the child’s mother. Section 33 of the Human Fertilisation and Embryology Act 2008 states that “the woman who is carrying or has carried a child as a result of the placing in her of an embryo or of sperm and eggs, and no other woman, is to be treated as the mother the child.” This can cause problems where a surrogate is used to carry the baby, as the parents of the child will not have any parental rights until such time as a court order (called a “parental order”) is made. In cases of this new therapy, however, no such problem arises. The woman who underwent assisted reproduction, is the genetic parent of the baby, and who thereafter went through the pregnancy and gave birth will be recognised as the baby’s mother. The fact that the healthy birth was helped along by donated mitochondria will make no difference to that.