Mary, a notional figure, is pregnant and looking forward to the birth of her baby. When, about 12 weeks into the pregnancy, she books into her local maternity hospital she has a scan. She is appalled to learn the doctors have identified a problem.

The baby is there all right, and appears normal. But there is something else which could be a tumour. There is no way of knowing whether or not it is malignant without removing it. This cannot be done except by emptying her uterus, thereby destroying the developing foetus.

Her obstetrician explains that, untreated, her condition is likely to lead to early pre-eclampsia, in which her blood pressure will rise to dangerous heights and put her at risk of heart attack or stroke. She might die.

This frightening prognosis can be averted by clearing out her womb, removing the tumour and the foetus. This is the same procedure as occurs in an induced abortion when a woman seeks one for social or psychological, rather than medical, reasons.

The woman and her partner discuss the matter and, when symptoms of pre-eclampsia emerge, they agree to have the pregnancy terminated. The obstetrician empties out the womb, thereby killing the foetus. But they are concerned that they have broken the law.

This is not abortion, according to the Pro-Life Campaign, which made a 70-page submission to the Interdepartmental Working Group on Abortion earlier this year. There is a difference, it says, between a medical procedure which has as a side-effect the killing of an unborn child, and induced abortion.

But some doctors do not see this distinction, and fear that if the Government introduces a new anti-abortion amendment to the Constitution as it has promised, it might compromise their ability to make the best clinical judgments, including, in a few cases, terminating a pregnancy.

The Master of the Rotunda Hospital, Dr Peter McKenna, is in no doubt about the decision to be made in the case of the woman with the molar pregnancy, as described above. "If she did not have her uterus emptied she would be dead."

He is aware of the "double effect" argument, but asks: "Can this principle of `double effect' be translated into law?"

But he is concerned about translating the complexities of medical practice and the rights of patients into simple constitutional statements. "As practising obstetricians our priority is to ensure that the mother does not die as a result of being pregnant."

Another critical condition for a woman's health during pregnancy is a rare form of heart disease where the heart and lungs are so damaged that there is only a 50 per cent rate of surviving childbirth. However, the condition also means that an anaesthetic is highly dangerous. "She is damned if she does [go ahead with the pregnancy] and damned if she doesn't," he said.

Ideally a woman with such a condition should not get pregnant at all. He had one patient who did, twice. The first time the baby died in utero. The second time the risks were explained to her, and she opted to continue with the pregnancy. The baby was born alive, but she died.

Such circumstances are extremely rare, but they do exist and must be taken into account. Women should be told if their pregnancy is posing a threat to their lives, and should be able to make an informed decision. Women often will continue with a pregnancy which threatens their lives, he stressed, and there are frequent cases of pregnant women suffering from cancer who refuse chemotherapy rather than threaten their baby.

A Pro Life Campaign leaflet, The Best Medical Care . . . states: "The lack of abortion facilities does not put women at risk. Study after study shows that whatever the medical problem, it can be treated without aborting the baby."

In its submission to the Interdepartmental Working Group, the PLC devotes a chapter to the medical questions on abortion. It states: "Abortion is never necessary to solve complications in pregnancy."

But, in an apparent concession that some life-threatening conditions may exist in pregnancy, it adds: "There is a real distinction between treatments presently regarded as ethical which may lead indirectly to damage or death to the unborn baby, and induced abortion . . ."

Dr Berry Kiely of the PLC explained: "You do not actually kill the baby. That's not the direct effect, and not the intention. The fact that the woman is pregnant is incidental to the treatment. Abortion does not treat the cancer. It is quite clear-cut that the woman is entitled to treatment irrespective of her pregnancy."

However, during the debate on the 1992 referendum, a group of 30 doctors wrote a letter to The Irish Times opposing the proposed amendment, which was attempting to rule out abortion on the grounds of suicide, while allowing it where the woman's life was in danger for medical reasons. This was defeated.

This letter stated: "If the amendment now proposed were to become part of the Constitution, the question would obviously arise as to what might be the fate of at least some babies whose mothers present with cardiac conditions or essential hypertension and the extent to which doctors, in the future, would be allowed to protect babies in utero. The question of what constitutes a substantial risk will always be highly subjective."

Dr Kiely explained that "if it is put into the Constitution `a substantial risk to the life of the mother' you can use that as a reason for abortion. You can use this terminology to suggest that there is a threat."

The Government is faced with the problem of reconciling many obstetricians' concerns with the promise it has made to have a new referendum on abortion.

Anti-abortion campaigners have been seeking this since the X case, when the Supreme Court ruled that abortion was legal when the life of the mother was in danger as a result of the threat of suicide.

A new referendum did take place after that judgment in 1992, but the wording did not meet the requirements of anti-abortion campaigners. It was also opposed by those against any abortion amendment in the Constitution, and it was defeated. Since then a new referendum, on a new amendment, has been sought by antiabortion campaigners.

Meanwhile, successive governments have been urged by those opposed to a new amendment to legislate on the basis of the X judgment instead, but have refused to do so.

This is the first time since 1992 that a new abortion referendum seems likely. But there is a mountain to climb in finding a wording which will meet the demands of the anti-abortion lobbyists, while not making doctors feel their practice might be in jeopardy.

The Government's temporary solution has been to set up the Interdepartmental Working Group, whose task is to draw up a Green Paper on Abortion. It is due to report at the end of the summer. Then the debate proper will begin, and eventually there will be a White Paper and then, maybe, the referendum.

Will this Government still be around to see it through?