DNA test cannot prove which identical twin is child's father

The Court of Appeal of England and Wales has concluded that it cannot identify which identical twin is the father of a child in a dispute regarding parental responsibility.

The child, referred to as P, was conceived after the mother had sexual intercourse with two identical twin brothers, referred to as TP1 and TP2, within a short window of time. Because identical – or monozygotic – twins start out as a single embryo they share a genome, and as such, a genetic test was able to confirm that one of the brothers is the genetic father, but not which one.

Sir Andrew McFarlane, president of the Family Division of the High Court of England and Wales, gave judgment for the Court of Appeal and first decided that, for the purposes of the Children Act 1989, a father is someone who is proved to be the genetic or biological father. In the case of P, the court ruled that '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', and that each of TP1 and TP2 had a 50 percent chance of being the father.

TP1 was originally listed as the father on P's birth certificate, and has another child with P's mother. The mother and TP2 subsequently mounted a legal challenge seeking to declare TP2 as P's father, grant him parental responsibility, and deny any parental responsibility to TP1. A lower court judge declined to make these changes, as she could not be sure TP2 is the biological father.

The Court of Appeal ultimately decided to remove any parental responsibility from TP1 arising from his name being on P's birth certificate, meaning that neither man is P's legal father.

The court terminated TP1's parental responsibility for two reasons. First, TP1 could not be proved to be P's genetic or biological father and thus was 'was not entitled' to be registered as the father in P's birth register entry. Secondly, as McFarlane said: 'It is plainly not in P's welfare interests for this ambiguity as to parental responsibility to continue.'

Although the court ruled that neither man can currently prove they are P's biological father, it refused to make a positive declaration that TP1 was not P's father, saying: 'There is a distinction between something being not proven, and making a positive declaration that the fact asserted is not true.'

The Court of Appeal noted that P's mother must think carefully about how to explain the situation to P as she gets older. It also 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.'