Double Trouble: The Unbelievable DNA Dilemma of a Mother and Twin Brothers

A complex legal case has reached the Appeal Court involving a woman who engaged in a sexual relationship with identical twin brothers simultaneously. The dilemma centers around determining the biological father of her daughter, as there remains a “50 percent chance” of paternity being attributed to either twin.

This unprecedented case, described as “highly unusual and possibly unique,” is believed to be a first in the UK, sparking debate over which twin should bear legal responsibility for the child.

The twin brothers, reportedly indistinguishable to the extent that the mother initially couldn’t differentiate between them, began separate relationships with her without each other’s knowledge after their initial meeting in 2017.

The woman gave birth to a daughter in 2018, who is now eight years old.

According to court records, the brothers discovered early in the pregnancy that they were both involved with the same woman. By the time she underwent her first ultrasound at 12 weeks, they were already debating via text messages about the likelihood of each being the girl’s father.

Both men had slept with the women during the four-day window in which she is thought to have conceived.

But while DNA paternity tests were carried out, each man returned a positive result and each believes that they are the girl’s biological father. The issue is understood to have driven a wedge between the brothers, who had previously been close.

The details of the case – which are anonymised – have emerged after it was initially brought before the family courts when local authorities encountered legal problems when attempting to make welfare arrangements for the girl, known as ‘P’ during the proceedings.

The extraordinary case, described as ‘highly unusual and possibly unique’, is thought to be the first of its kind in the UK and has raised questions over which man should have legal responsibility for the child (stock image)

The woman had remained in a casual relationship with one of the twins, and he is named as P’s biological father on her birth certificate. 

This automatically gives him legal responsibility for her – which means he is entitled to make decisions on her life and welfare, such as where she lives and her education.

But that relationship broke down. When local authorities sought to apply to the courts to make a child arrangement order over custody, they discovered that the girl’s paternity was contested by the other twin.

A fact-finding hearing at the family courts in 2024 was tasked with establishing which twin was likely to be P’s father.

But Judge Reardon, who presided over the case, was unable to make a ruling because the evidence suggested it could be either twin.

In her ruling, she said: ‘They have both claimed her; and they are both pursuing this claim at considerable financial and personal cost, including a cost to their own relationship which, before this issue arose, was close.’

It has now come before the Court of Appeal after legal representatives appointed on behalf of P challenged that decision and sought to remove the twin from her birth certificate to prevent any ‘ambiguity’, which would then also remove his right to parental responsibility.

Emma Hubbard, senior associate at Hall Brown Family Law, said: ‘The circumstances of this case are relatively unusual. 

‘I certainly can’t think of another one involving the same complications.

‘Where no definite biological link can be proven, it means a child may grow up having only a mother with parental responsibility for them.’

Standard DNA paternity tests used in science and law are extremely reliable, but even they cannot distinguish between identical twins.

They examine small regions of the father’s DNA and compare it to the child’s, which is usually enough to confirm paternity with over 99.9 per cent certainty.

But identical twins come from the same fertilised egg which divides during the early stages of development – which means they share almost all their DNA.

The only way to tell them apart is by conducting an analysis of their entire DNA – known as whole genome sequencing – which can pick up tiny mutations which may have taken place after the egg split in two.

In a judgement published last week, the Court of Appeal ruled that the twin on the birth certificate should remain there because ‘it is simply not possible to hold that [the twin] is not P’s father, indeed, there is a 50 per cent chance that he is’. Pictured: The Court of Appeal based at the Royal Courts of Justice in London

The court heard such an analysis would cost in the region of £90,000 – making it out of reach for those involved – and it may not, even then, be conclusive.

James Ware, a professor of cardiovascular and genomic medicine at Imperial College London, said: ‘There is a window in which twins’ developing embryos can acquire a few mutations that distinguish them after the egg has split.

‘That number can be very, very small – the average is five, but it can be up to 100 – among our three billion letters of DNA.

‘Those mutations will only be passed on to a child if they are contained in sperm, so analysing their sperm might help distinguish between the men, although there are no guarantees.’

A similar case emerged in Brazil in 2019 when a woman became pregnant after sleeping with one identical twin – but because neither twin would take responsibility, and DNA tests were unable to distinguish between the two, a judge ordered both to pay child support.

In a judgement published last week, the Appeal Court ruled that the twin on the birth certificate should remain there because ‘it is simply not possible to hold that [the twin] is not P’s father, indeed, there is a 50 per cent chance that he is’.

But it ruled that an order should remove his right to parental responsibility.

The ruling said: ‘It is possible, indeed likely, that by the time P reaches maturity it may be possible for science to identify one father and exclude the other twin, but, for the coming time that cannot be done without very significant cost, and so her “truth” is binary and not a single man. It is for [her mother] to determine how P is introduced to this truth over time.’

The case, heard by Sir Andrew McFarlane, President of the Family Division, has clarified the law in terms of parental responsibility, Emma Hubbard said.

‘Over the years, courts have questioned whether someone can only really be a father with parental responsibility if there is a biological link to a child,’ she said.

‘This judgement indeed means just that. If there is no biological connection, there can be no parental responsibility, regardless of whether someone is named on a birth certificate.’