The hearing could have an impact on plans for an Eighth Amendment referendum
Counsel for the State have argued in the Supreme Court that a person is not entitled to full protection under the constitution until they are born.
The State is appealing a High Court decision which said the constitution contains more than just the right to life for the unborn child.
The State's argument is that you don't get your constitutional rights as a person until you are born.
Before that the unborn only have the right to life, as set out in the 8th amendment.
They are appealing a High Court decision which ruled the unborn had the same rights as a child.
Senior Counsel for the State, Mary O'Toole, said accepting that viewpoint would mean every unborn person in the State since 1937 had general rights without exception - which she called a radical statement.
She said taking that viewpoint may lead to restrictions on pregnant women.
She asked how to protect the rights of the unborn in the womb - and said it could for example lead to the government forcing all pregnant women to take folic acid.
In the court today, they have argued the Constitution contains no other fundamental right for the unborn, beyond the right to life outlined in the 8th amendment.
The State contends that, prior to 1983, there was no definitive statement on the rights to the unborn in the Constitution.
The case arises out of an immigration case, where a Nigerian man opposed his deportation on the grounds his partner was pregnant with his child who would have Irish citizenship.
Their lawyers will argue there are extensive rights for the unborn in the constitution, when the trial resumes tomorrow.
This has significance if the seven-judge Supreme Court were to agree.
The Government's plans for an abortion referendum are to seek a vote to repeal the 8th amendment, and then to legislate for terminations.
However, if it is upheld that the unborn has other rights in the constitution beyond the 8th, those plans could be derailed.
The ruling could also have implications for how the State deals with expectant mothers.
The Appeal continues tomorrow.