The European Court of Human Rights is to rule on whether Irish anti-abortion laws violate women's human rights.
The case was brought by three women who say their health was put at risk by having to travel abroad for abortions.
The government argues that the Republic must retain the sovereign right "to determine when life begins".
Thursday's ruling could require a change in Irish law. Abortion is illegal there but technically allowed if a woman's life is at risk.
However, at the original hearing at the Strasbourg-based court in December 2009, a lawyer for the women argued that the reality under Irish law was that doctors could lose their licence or face jail if a woman's life was later found not to have been at risk.
In 1992, the Irish Supreme Court ruled that termination should be allowed if a woman's life was at risk, but that ruling has never been adopted in Irish law.
The issue has divided the deeply Catholic nation.
The Irish Republic has become much more liberal and secular in recent years, says the BBC's Mark Simpson in Dublin, but there is still strong opposition to abortion in many quarters.
It is estimated that more than 4,000 Irish women every year have an abortion overseas, most of them in England.
'Profound moral values'
The lawyers for the three women have argued that having to leave their country for an abortion was humiliating and caused them distress and health complications.
Their identity has been kept confidential, but two are Irish and one is a Lithuanian national living in the Republic. They are known only as A, B and C.
They went to the UK to have abortions after becoming pregnant unintentionally. One woman was at risk of an ectopic pregnancy, where the foetus develops outside the womb, while another woman was undergoing chemotherapy for cancer.
The third was a former alcoholic who feared having another child would jeopardise her chances of getting her first four children out of foster care.
If the court rules in the women's favour, as a signatory to the European Convention on Human Rights the Republic of Ireland would be obliged to accept any changes to its law the court recommends.
But the court could rule that medical treatment and advice were available in the Republic or that the women did not take their case first to the Irish courts, as the Convention requires.
The Irish government has argued that in the past the Convention has recognised individual state's traditions regarding the rights of unborn children and that the country's abortion laws were based on "profound moral values deeply embedded in Irish society".