The more abortions a woman has before her first child, the more likely she is to give birth to prematurely born babies, a study has suggested.
Data from all 300,858 first-time mothers in Finland between 1996 and 2008 was analysed.
The study showed women were three times more likely to have a very premature baby, born before 28 weeks, if they had three or more abortions.
The report was published in the journal Human Reproduction.
The overall risk was still low, the study suggested.
Being born too soon is linked to higher risks of infection, hypothermia and death.
The study showed there would be three babies born before 28 weeks for every 1,000 women who had never had an abortion, four per 1,000 who had had one abortion, six in those who had had two abortions and 11 if the woman had had three or more abortions.
There were similar figures for babies born before 37 weeks and for low birth weight. However, only 0.3% of women in the study had had three or more abortions before their first child.
An increase, after three or more abortions, of nearly threefold in the odds of having an infant born before 28 weeks is worrying”
The lead researcher Dr Reija Klemetti, from the National Institute for Health and Welfare in Helsinki, 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 way the study was designed means the researchers cannot say for certain that abortions result in premature births, merely that they had spotted a link between the two.
However, they suggest that surgical abortions could increase the risk of infection, which could affect future pregnancies.
Statistics for England and Wales show the number of women having multiple abortions is rising.
Andrew Whitelaw, a professor of neo-natal medicine at the University of Bristol, said: “While pre-term birth before 37 weeks’ gestation exposes an infant to a modest but definite increased risk of a range of serious problems including brain injury and death, 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.
“The steadily increasing survival of very pre-term infants should not be interpreted as a solution to the problem of pre-term birth. Increased survival of infants under 28 weeks is at the cost of increased survival of infants with disability.”
By James Gallagher, Health and science reporter, BBC News