The Three Parent Baby Phenomenon

Is it an innovative method that will prevent diseases caused by mutations in mitochondrial DNA (mtDNA) or a threat to humanity? Scientists have thoroughly debated the three-parent-baby phenomenon, especially since the United Kingdom became the first country to legalize mtDNA transfer in February 2015 [1].

The term “three-parent-babies” refers to infants born through an in-vitro fertilization where the mitochondria are transferred from a healthy female donor to the mother’s egg. Babies born this way are called “three-parent babies” because they have genetic material from the donor woman and their biological parents.

In the late 1990s, some private clinics in the United States began performing an experimental technique known as cytoplasmic transfer. The U.S. government outlawed this technique in 2002. [2] The main difference between this—now obsolete—technique and the method currently used is that the mitochondria from two women would be mixed in the former technique, while nowadays, scientists perform a method in which the donor’s mitochondria completely replace the ones that already existed in the mother’s egg [3]. Researchers in the U.K. have recently introduced two variations of this procedure.


The first one is called pronuclear transfer. As the name suggests, this specific method is based on pronucleus, a cell nucleus with a haploid set of chromosomes (23 chromosomes in humans) resulting from meiosis (germ-cell division). The male pronucleus is the sperm nucleus after it has entered the ovum at fertilization, but before fusion with the female pronucleus. Similarly, the female pronucleus is the nucleus of the ovum before fusion with the male pronucleus. Pronuclear transfer begins with an in vitro fertilization that makes use of the mother’s egg (with mutated mitochondrial DNA) and the father’s sperm. The pronuclei are removed from this mother’s fertilized egg and placed in a donor’s egg, with removed and destroyed pronuclei. Father’s sperm fertilizes the donor’s egg as well. Then the egg with the parents’ pronuclei and the healthy mitochondria from the donor proceeds to grow and develop naturally, resulting in a three-parent baby.

In the second variation, called maternal spindle transfer, the mitochondria is repaired before fertilization. In this type of the procedure, chromosomes are removed from an unfertilized egg that contains mutated mitochondrial DNA and are added to an unfertilized donor egg that has had its nucleus removed. The in vitro fertilization happens at this point and then the egg develops and starts to form an embryo [4].

Can a baby really have three parents? Should the child be allowed, once he or she reaches adulthood, to know who the donor is, or should the donor’s anonymity be protected? Could the donor file a child custody claim for this baby?

This specialized method aims to prevent the inheritance of disease-causing mitochondria [5]. Mitochondrial diseases are passed down from the mother to the child. Even though the sperm also contains mitochondria, it does not contribute any mtDNA to the embryo [6]. Therefore, all of the embryo’s mitochondria originate from the mother. During mtDNA transfer, the mother’s unhealthy mitochondria are replaced by healthy ones from a donor. Mitochondrial disorders are considered to be the cause of a number of serious diseases, some of which can be fatal. No way of preventing these diseases has been found up until now [7]. Since this method is legalized in U.K., some deaths and unfortunate illnesses may be prevented.

However, this method still raises a plethora of questions. Firstly, who of these three people are the child’s parents? Can a baby really have three parents? Should the child be allowed, once he or she reaches adulthood, to know who the donor is, or should the donor’s anonymity be protected? Could the donor file a child custody claim for this baby? In the case where both the biological parents die, should the child remain with their family, or could the donor take legal custody? All of these questions indicate the importance of introducing a legislation that regulates the various aspects of this topic.

As far as parenthood is concerned, it is almost without doubt that the man and the woman who originally provided their genetic material with the purpose of reproduction are the baby’s biological parents. It is estimated that almost 99.8% of a cell’s DNA is contained in the nucleus. All of this comes from the parents. The donor only contributes their mtDNA, which accounts for a very small fraction of the cell’s total DNA. The genes that mitochondria contain are responsible for the production of energy in the body, but conventional scientific knowledge is that mtDNA plays no role in determining the way a person thinks or acts and thinks [8] nor does it affect the person’s physical appearance [9].

However, more recent studies have showed that mitochondria actually affect some of the physical features of an individual [10].There is also concern about the future generations. It has been known for quite a few years now that women pass their mitochondria on to their descendants [11]. Every female born through one these procedures can pass the modifications caused by the treatment on to their children.

Whether mtDNA transfer will eventually be legalized in more countries apart from UK is still unknown. British citizens are becoming increasingly aware of the method and some are concerned. The majority had a negative reaction the first time they heard about this controversial medical technique. However, a lot of them turned positive once the implications of the procedure had been explained [12]. It is certain that more research is needed and that scientists are still not sure of the effects those techniques could have on future generations. It appears however that a lot of people have started to believe that the benefits outweigh any possible risks.


[1] Laura Smith-Spark. “UK lawmakers vote to allow ‘3-parent’ babies”. CNN (2015). Available from: URL:

[2] Connor Steve. “Medical dilemma of three-parent babies: Fertility clinic investigates health of teenagers it helped to be conceived through controversial IVF technique”. The Independent. (2014). Available from: URL:

[3] Donnelly Laura. “Three-parent babies: good or bad?” The telegraph. (2014). Available from: URL:

[4] Pritchard Charlotte. “The girl with three biological parents”. The BBC. (2014). Available from: URL:

[5] “Hello mothers, hello father”. The Economist. From the print edition. Available from: URL:

[6] Maynaed James. “UK sets up rules for three-parent babies to be born”. Tech Times.(2014). Available from:URL:

[7] Sample Ian. “Three-person IVF: UK government backs mitochondrial transfer”. The guardian. (2013). Available from: URL:

[8] Collins Nick. “Three-parent baby fertility technique could be made legal”. The telegraph. (2012). Available from: URL:

[9] Cassidy Patricia. “Draft regulations on mitochondrial donation published”.(2014). Available from: URL:

[10] “Three-parent babies: It’s more messy than we thought”. New Scientist. (2014). Magazine issue 2987. Available from: URL:

[11] Clark Liat. “In depth: three-person IVF is about saving lives, not a slippery slope to eugenics”. WIRED. (2013) Available from: URL:

[12] T.C. “How a baby can have three parents”. The Economist. (2014). Available from: URL:

Further reading:

[1] Report provided to the Human Fertilization and Embryology Authority (HFEA), June 2014. “Third scientific review of the safety and efficacy of methods to avoid mitochondrial disease through assisted conception”

[2] Gander Kashmira comments on mitochondrial replacement therapy and any possible effects a few months before it was legalized in the U.K.

[3] U.K. draft legislation surrounding the human fertilization and embryology (mitochondrial donations) regulations.

Image Credit:

[1] Vintage Arizona State University mitochondria model. Gregory Han. Accessed April 4, 2015.


Zina Tsitrouli is currently studying law at the Aristotle University of Thessaloniki. She is interested in bioethics and would love to follow a career in human rights law. Follow The Triple Helix Online on Twitter and join us on Facebook.