Doctors are the first group of experts to give evidence as part of four separate sessions before the Oireactas Committee on Health and Children which will be held over the next three days.
The committee has been charged with informing the drafting of new controversial new laws and regulations on abortion to finally enshrine the 1992 X Case ruling in legislation.
So many TDs and Senators want to address the group that the meetings have been moved to the Senead chamber to accommodate the large group. More than 40 experts and campaigners will make submissions on the medical, legal, religious and social aspects of the issue.
Conservative Fine Gael TDs are expected to make a forceful case with party members deeply uneasy over legislation for the suicide risk.
It is expected that, over the three days, more than 100 TDs and Senators will express their views and question experts.
Committee chairman Jerry Buttimer has called for a calm and dignified debate allowing all sides to have their voices heard.
"It is a very important issue. It's a very complex one. It's one that has divergent viewpoints but what we must do here is we must consult, we must listen and then we must implement and that is what the Government will do."
Mr Buttimer said the committee will "inform and lead the debate".
The cross-party group will report to the Government by the end of this month on what it has heard.
The hearings get under way as Pope Benedict XVI has expressed "dismay" at the proposed introduction of abortion legislation "in various countries even those of Christian tradition".
In what Vatican insiders suggest was an intentional veiled reference to Ireland, the Pontiff said he was dismayed that even in Christian countries "efforts are being made to introduce or expand legislation which deciminalises abortion".
Pope Benedict made his remarks during his annual keynote address to the Vatican's diplomatic corps.
Today's medical experts addressing the hearing include Dr Rhona Mahony, Master of the National Maternity Hospital, Dr Sam Coulter Smyth, Master at the Rotunda Hospital, Dr John Sheehan, College of Psychiatry Ireland, Prof Veronica O'Kane, Department of Psychiatry, Tallaght Hospital and Niall Behan of the Irish Family Planning Association.
Prof Robert Harrison, Dr Meabh Ni Bhuinneain and Prof Fionnuala McAuliffe, of the Institute of Obstetricians and Gynaecologists, and Prof richard Green of Maternal Death Inquiry Ireland are also giving their views.
Tomorrow the emphasis will be on the legal aspects. On the final day, Church leaders will appear before the committee.