Women who have had several abortions are more likely to have a premature or low-weight baby when they subsequently have a child, according to a large study from Finland.

The study is one of the biggest to look at the consequences from abortion and found that there was an extra risk, but only for women having their first child who had undergone three or more abortions. Even then, it was small.

Dr Reija Klemetti, an associate professor and senior researcher in public health at Helsinki's National Institute for Health and Welfare, who led the research, said: "Our results suggest that induced abortions before the first birth, particularly three or more abortions, are associated with a marginally increased risk during the first birth.

"However, the increased risk is very small, particularly after only one or even two abortions, and women should not be alarmed by our findings."

The study, published in the journal Human Reproduction, looked at the outcomes from the pregnancies of more than 300,800 women between 1996 and 2008. More than 10% had undergone one abortion, 1.5% had experienced two and 0.5% (942 women) had undergone three before a first birth.

The researchers found that first-time mothers with previous induced abortions "were more often smokers, single, from urban areas and from a lower socioeconomic position, and had had miscarriages and ectopic pregnancies before their first birth".

But when they allowed for these factors, it became apparent that there was still a small increased risk linked to multiple abortions. Those who had undergone three or more were slightly more likely to have a baby of very low birth weight (less than 1500g), low birth weight (less than 2500g), preterm (before 37 weeks) or very preterm (before 28 weeks) compared to those who had never had an abortion. There was a slight increased risk of a very preterm birth also for women who had undergone two abortions.

"To put these risks into perspective, for every 1,000 women, three who have had no abortion will have a baby born under 28 weeks," said Dr Klemetti. "This rises to four women among those who have had one abortion, six women who have had two abortions, and 11 women who have had three or more."

She added that there might still be social factors that they had not allowed for, related to some women's way of life, life habits, and sexual and reproductive health. She said also that the study could show a link, but not prove that abortion was the cause.

Andrew Whitelaw, professor of neonatal medicine at the University of Bristol, said the study was of high quality and the results should be shared with women seeking abortions.

"Birth before 28 weeks exposes the infant to a hugely increased risk of death, brain injury and permanent disability. Thus an increase (after three or more abortions) of nearly threefold in the odds of having an infant born before 28 weeks is worrying," he said.

He noted also that most women in the study had undergone surgical abortions and that there could possibly be less risk in medical abortion, where drugs are used to induce it.

Dr Patricia Lohr, BPAS Medical Director, said that the risk, if it exists, is small. "For most women the foremost consideration when faced with an unplanned pregnancy is whether they feel in the position to carry that pregnancy to term and become a parent, or add to their existing family."