Irish lawmakers were voting Thursday on historic legislation to introduce abortion in limited cases where the mother's life is at risk.
Weary lawmakers voted through the night with results expected at 5.00am local time (0400GMT).
The predominantly Catholic nation's abortion laws faced global scrutiny after the death of 31-year-old Indian woman Savita Halappanavar in a Galway hospital last October.
The bill follows a 2010 European Court of Human Rights ruling that found Ireland failed to implement properly the constitutional right to abortion where a woman's life is at risk.
Under a 1992 Supreme Court ruling, women in Ireland are legally entitled to an abortion if needed to save a mother's life -- but six successive governments have failed to introduce legislation to reflect this.
The Protection of Life During Pregnancy Bill would allow for abortion in circumstances where doctors certify there is a real and substantial risk to the life of the mother, as opposed to just a health risk.
The new bill also permits a termination when one obstetrician and two psychiatrists unanimously agree that an expectant mother is a suicide risk.
The "suicide clause" has caused consternation among some lawmakers who believe it will be abused and lead to more abortions in Ireland.
Particular attention was focussed on on Lucinda Creighton, junior minister with responsibility for European Affairs and a member of Prime Minister Enda Kenny's Fine Gael party, who threatened to vote against the government over misgivings on the suicide clause.
"I very much support the overall intention of the legislation which is supposed to be about protecting and saving the lives of women and babies - but I cannot support a clause which is essentially built on sand," Creighton said during discussions on amendments to the bill Wednesday evening.
"Please let's not enshrine flawed logic, flawed legislation on our statute books which will be irreversible.
"The legislation may be reversible but the consequences of the legislation are not reversible," she added.
"It will change the culture in this country and it will change how we deal with vulnerable women."
Kenny has not allowed a free vote on the matter, with four government deputies expelled from the parliamentary party after voting against the bill at an earlier stage.
The Halappanavar case highlighted the problematic legal situation in Ireland regarding abortion.
She had sought a termination when told she was miscarrying, but the request was refused as her life was not deemed at risk at the time. She later died of sepsis days after miscarrying.
The bill has caused intense debate with around 35,000 opponents attending a march in Dublin last Saturday.
A number of protestors held a silent vigil outside parliament Wednesday night.
Kenny revealed recently he had received abusive letters written in blood and was branded a murderer from people opposed to the bill.
Others have argued that the bill is too limited as it does not allow termination in cases of foetal abnormalities, or in cases of incest or rape, and would not have saved the life of Halappanavar, as doctors did not believe there was risk to her life when she requested the termination.
UK Department of Health statistics show 4,149 women travelled from the Republic of Ireland for an abortion in 2011.
Between 1980 and 2011, over 150,000 women travelled from Ireland to the UK for a termination, according to the figures.
If successful, the bill will go to a vote in the upper house, where the government enjoys a majority.