The High Court has heard that the genetic parents of twins born to a surrogate mother could face possibly insurmountable legal hurdles if they were to try to adopt the children.

On the final day of the case, lawyers for the couple said because the twins were born to their aunt, who was married at the time, they could not be placed for adoption.

Senior Counsel Gerard Durkan said adoption as a proposed remedy was unsatisfactory.

It would require the couple to take a second case in another area of law without precedence.

Mr Durkan said they would have to show the children had been abandoned, which would be difficult to do.

He was responding to submissions made yesterday by counsel for the State Mary O'Toole, who said the couple could apply to adopt the twins.

The State is also opposing the application on the basis that only the birth mother can be viewed as the legal mother.

Ms O'Toole said yesterday the 1983 abortion amendment to the Constitution made it "absolutely clear" that the mother of a child was the woman who gave birth to the child.

She was defending the refusal of the State to allow the genetic mother of twins born to a surrogate mother to be listed as the children's mother on their birth certificates.

Mr Durcan said this was an incorrect interpretation of the Constitution.

Those who voted in the 1983 referendum were only addressing the issue of the baby in the womb and not after birth, he said.

Mr Durkan said the Supreme Court had established in the frozen embryo case that the protection of the embryo in the context of the right to life in the constitution only applied after implantation.

Just as it did not apply before implantation, it did not apply after birth in this particular context, he said.

Responding to the points made on adoption, Ms O'Toole said it was not the case that the twins would be considered part of a constitutional family of the surrogate mother and her husband as the husband had signed a declaration acknowledging the children were not his.

However, Mr Durkan said they would still face extensive legal hurdles because of the unusual nature of the case.

The case has now concluded.

It will be mentioned before the court on 22 February when Mr Justice Henry Abbott is expected to give a date for judgment.