A woman who gives birth to a child may not be the "mother" in the traditional sense because there have been such major scientific advances in reproduction, a landmark High Court case heard.
The genetic parents of twins born to a surrogate mother are seeking to have their children's birth certificates amended to name the genetic mother rather than her sister who bore them.
Gerard Durcan, counsel for the couple, argued it was "always a good idea if law reflects reality", which now means that the woman who gives birth may not be the genetic mother.
He suggested it should be a "rebuttable presumption" and not an "absolute" that the woman who carries the baby to term is in fact the mother. This is true in cases where scientific DNA evidence can be produced to show otherwise, he said.
The landmark legal challenge has begun raising issues never before considered by an Irish court. None of the parties can be identified for legal reasons.
The married couple took the case on behalf of the children, with the support of the woman's sister who acted as surrogate. They want to have the genetic mother's name registered on the birth certificate, instead of the surrogate. They were told by the Office of the Registrar General in 2011 that the genetic mother's name could not be listed on the birth certificate as a matter of law.
Chief registrar Kieran Feely said he had to apply the principle that "motherhood is always certain".
Mr Durcan argued scientific evidence, that the sister was not the genetic mother, could not just be ignored.
The court heard claims from counsel that there would be "serious adverse" implications for the rights of the twins and they would be deprived of the "security" that comes with being part of a family recognised under the Irish Constitution.
Mr Durcan said the genetic mother "has fulfiled the role of mother in every practical aspect since birth". A fallback option for the couple, he suggested, was that they be appointed guardians of the twins but he described it as a "very poor second".
The case continues today.