Key Points:

Women who have an abortion have an increased risk of developing mental health problems, New Zealand researchers have found.

The long-term Christchurch study of more than 500 women found a link between having an abortion and an increase of nearly a third in the risk of disorders such as depression and anxiety.

Reporting their findings in the British Journal of Psychiatry, the Otago University researchers say that abortions account for 1.5 to 5.5 per cent of the overall rate of mental disorders.

They said their study backed up others overseas which concluded that having an abortion may be linked to an increased risk of mental health problems.

But a pro-abortion group said yesterday that international evidence was inconclusive.

It was likely that the effect of abortion on mental health was small or negligible and closely linked to factors that led to unplanned pregnancies, said the president of the Abortion Law Reform Association, Margaret Sparrow.

She cited the findings of an American Psychological Association taskforce on mental health and abortion.

The taskforce's chairwoman, Dr Brenda Major, said in August that the best published scientific evidence indicated that among adults who had an unplanned pregnancy, the relative risk of mental health problems was "no greater if they have a single elective first-trimester abortion or deliver that pregnancy".

"The evidence regarding the relative mental health risks associated with multiple abortions is more uncertain."

The University of Otago team, Professor David Fergusson, John Horwood and Dr Joseph Boden, said their findings pointed to a middle-of-the-road view on abortion - one which supported neither strong pro-abortion nor anti-abortion positions.

The mental health problems most closely linked to abortion in their study included anxiety disorders and substance abuse.

"Other pregnancy outcomes [including live birth] were not related to increased risk of mental health problems."

They said the study had implications for the legal status of abortion in New Zealand and Britain where more than 90 per cent of abortions were authorised on grounds of serious threat to the woman's or girl's mental health if her pregnancy proceeded.

The women in the study were interviewed six times between the ages of 15 and 30 and their mental health was assessed each time.

Overall, 284 women reported a total of 686 pregnancies before the age of 30.

They included 153 abortions performed on 117 women, 138 miscarriages and other pregnancy losses, 66 live births from pregnancies that were unwanted or provoked an adverse reaction and 329 live births from wanted pregnancies.

A High Court judge this year expressed "powerful misgivings" about the legality of many abortions, suggesting that New Zealand in effect had abortion on demand.

The Abortion Supervisory Committee is appealing against the decision in the case brought by the anti-abortion group Right to Life.

Anti-abortion group Family First said the growing evidence of potential harm of abortion to the mother meant the abortion debate should be re-opened.