Identical Twins DNA Test Paternity Ruling

Inner Temple Library Current Awareness

Filed March 30th, 2026

Detected April 1st, 2026

Summary

The Court of Appeal in England and Wales ruled that DNA testing cannot determine which identical twin fathered a child when both had intercourse with the mother within four days of each other. The court removed parental responsibility from the twin currently on the birth register, stating it was not possible to identify the biological father between the two genetically identical brothers. The matter has been referred back to a lower court for further determination of parental responsibility.

View original document View source feed page

What changed

Sir Andrew McFarlane, sitting with Lady Justice King and Lord Justice Stuart-Smith, handed down a judgment in the case involving 'Child P' where DNA testing revealed either of two identical twins could be the father but could not distinguish between them. The court found the registered twin 'was not entitled' to be on the birth certificate and ordered his parental responsibility to cease, but declined to make a positive declaration that he was not the father. The court held that 'there is a distinction between something being not proven, and making a positive declaration that the fact asserted is not true.'\n\nLegal practitioners and family courts should note that this ruling establishes precedent that identical twin paternity cases require case-by-case judicial determination when DNA testing is inconclusive. Lower courts must now determine 'either, both or neither of the twins should now be granted parental responsibility' in light of the binary truth that only one twin is the biological father but science cannot currently identify which one.

What to do next

Review court judgment EWCA Civ 2026/344 for full reasoning on inconclusive twin paternity cases
Advise clients with identical twin paternity disputes that neither twin can be presumed father when DNA is inconclusive
Note that courts may await future scientific advances before making final paternity determinations

Source document (simplified)

The court of appeal judge Sir Andrew McFarlane said the twin who had been on the birth register will have parental responsibility removed until the court hears further arguments. Photograph: Nikreates/Alamy

Children

Court of appeal says it cannot rule on which identical twin fathered a child

One twin wanted to take parental responsibility from the other for child P after both had sex with child’s mother

Matthew Weaver

Mon 30 Mar 2026 12.31 EDT

Last modified on Tue 31 Mar 2026 00.10 EDT

Share Prefer the Guardian on Google

A woman who had sex with identical twins within four days of each other is unable to ensure one of them takes parental responsibility because it is “not possible” to know which is the father, the court of appeal has said.

One of the twins was registered as the father on the birth certificate of the child, referred to as P. His identical twin, along with the mother, sought to take over parental responsibility by asking the court of appeal to overturn a previous family court decision.

Sir Andrew McFarlane, sitting with Lady Justice King and Lord Justice Stuart-Smith, said that while DNA testing has revealed that either of the twins could be the father, it cannot distinguish between them so there is a 50% chance of the correct father being already on the birth certificate.

He said the twin on the birth register will no longer have parental responsibility until the court hears further arguments.

The identities of the child, the twins and the mother have been protected by the court.

In a judgment handed down earlier this month, McFarlane said: “Currently the truth of P’s paternity is that their father is one or other of these two identical twins, but it is not possible to say which.

“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.”

Judge Madeleine Reardon previously found that “both brothers had had sex” with the woman “within four days of each other in the month when P was conceived”, and that “it is equally likely that each of the brothers is P’s father”.

McFarlane said that the first twin “was not entitled” to be registered as the father and that any parental responsibility he had as a result “shall cease”.

But he said that he was “wholly unpersuaded” to declare that this first twin was not the father.

He added: “The failure to prove a fact means that that fact is not proved, it does not mean that the contrary is proved.

“There is a distinction between something being not proven, and making a positive declaration that the fact asserted is not true.”

McFarlane said it was “plainly not in P’s welfare interests for this ambiguity as to parental responsibility to continue”. He added it would be for a lower court to determine “either, both or neither of the twins should now be granted parental responsibility”.

Explore more on these topics
- Children
- news