The High Court has been told it be must be satisfied there is no real possibility of an unborn child's survival before backing any action which would bring that life to an end.
The submission was made by lawyers representing the unborn child in the case of a pregnant woman who is on life support.
Her family want the life support treatment to be stopped to allow her to be put to rest.
Three judges of the court heard legal submissions on behalf of all parties in the case and will give its decision at midday on St Stephen's Day.
The court heard yesterday that the woman at the centre of this case was declared brain dead 21 days ago and that the chances of her unborn child being born alive were small.
Doctors would not turn off the life support as they were unsure about the legal position of the unborn child under the Constitution.
This morning, Senior Counsel for the woman's family, Mary O'Toole, said the prospects of this unborn child surviving to be viable were small to almost negligible.
She said however if the court took the view that the unborn's right to life was engaged in this case then the issue was what was practicable in the circumstances of this case.
She said it was not just a question of the foetus surviving but how it would be affected by the drugs and chemicals being pumped into its mother's body.
She asked if it was in the best interests of the unborn to be maintained in an environment where it had extremely poor prospects of survival.
She said this was not a case about abortion. This was an act of god where the child's mother had suffered the dreadful catastrophe of brain injury.
She said the family's interests also had to be recognised as a matter of human decency and understanding.
The father had not only suffered the nightmare of his child pre-deceasing him, he had to watch her deteriorating in what was "akin to a horror movie" and the family were enduring an unimaginable level of suffering.
Lawyers for the HSE said this was not a case about international statistics. This was a case about people.
Senior Counsel Gerry Durcan said the crucial evidence in the case was about this particular unborn child in the body of this unfortunate woman.
He said the court had to have regard to the best interests of the unborn child.
And he said the mother was entitled to dignity in death as she would have been in life.
He said doctors had found themselves in a very difficult position.
He added that doctors needed reassurance that their view about the best interests of a patient in their clinical judgment should carry very considerable weight and that they can trust their clinical judgment.
He said the court should declare that discontinuing life support treatment would be lawful in the particular circumstances of this case.
He said this would allow doctors to exercise their clinical judgment in the best interests of the unborn and deal with the body of the mother with respect and dignity.
Lawyers for the unborn child said they agreed this case was not about abortion.
Senior Counsel Conor Dignam said the key issue was what was practicable to vindicate the rights of the unborn child.
He said the mother's right to life was no longer engaged as she was dead. He she may have a residual right to dignity in death but the right to life of the unborn child would take precedence over that right.
He said there was a difference between the Irish and English texts of the eight amendment.
The English text said the rights of the unborn had to be defended "as far as practicable". The Irish text said "as far as possible".
He said the court must be satisfied there was no real possibility of the survival of the unborn child before backing any action that would bring that life to an end.
Lawyers for the mother said they were not conceding that she was dead.
Senior Counsel Cormac Corrigan said they accepted her state was irreversible.
He said there was no direct evidence of her wishes, however there was evidence from which the court could infer her views of what she would have wanted.
He said the court did not have to determine what amounts to death.
He said if it did determine that question, it might have to hear further evidence.
He said the woman was not suffering at the moment.
He said she may have a right to die with dignity but there was no question of her at this stage having any dignity. She was in a situation as undignified as you could imagine.
He said an intensive care specialist yesterday had said he could not say it was impossible to continue life support treatment.
He said the treatment was described as experimental and grotesque.
But he said one person's experiment may be another person's pioneering treatment or another person pushing the boundaries, or deciding what the law permits.
Was this a pioneering case pushing the boundaries of the law?, he asked.
The court will give its ruling at midday on St Stephen's Day.