Lead researcher Dr Reija Klemetti, of the National Institute for Health and Welfare in Helsinki, said the increased risk was ‘very small, particularly after only one or even two abortions, and women should not be alarmed’.
‘Furthermore, this is an observational study and, however large and well-controlled, it only shows there is a link between abortion and some adverse birth outcomes – it cannot prove that abortions are the cause.’
However, she urged young girls to be told of the possible harms linked to repeat abortions.
The study – published in Human Reproduction – also showed an increased risk of a baby’s death around the time of birth, but the researchers say this could be because of social factors such as poverty.
Dr Klemetti said: ‘Our study is the first large study to look at a broad set of perinatal outcomes and to control, at least partly, for the most important confounding factors such as smoking and socioeconomic position.
‘However, it is important to say that even though we adjusted for these factors, and also ectopic pregnancies and miscarriages, there might be some confounding for social class that we could not control for.
‘Most probably, this may be related to women’s (or some of these women’s) way of life, life habits, and sexual and reproductive health.