Women who have their baby by caesarean section are less likely to have another pregnancy, a 17-year study following 25,370 women revealed yesterday.

Researchers also found that the average amount of time between births was greater for those who had undergone caesareans than those who gave birth naturally.

More than one in five women in England have caesareans and the rate is rising, provoking concern over risks to women and babies.

The latest study, based on the Aberdeen maternity hospital between 1980 and 1997 and published in the British Journal of Obstetrics and Gynaecology, was not able to determine whether the women's fertility was being compromised by having a caesarean, by suffering tubal damage for instance, or whether women who had undergone the experience just did not want to do so again.

However, lead researcher Jill Mollison, of Aberdeen University's medical school, highlighted the importance of the findings against the background of rising caesarean rates. "Future studies should focus on exploring whether failure to conceive is due to voluntary or involuntary factors and compare this across different modes of delivery."

Peter Bowen-Simpson, from the Royal College of Obstetricians and Gynaecologists, said: "Those involved in the delivery of obstetric care should be aware of the association and consider its implications when making a decision to perform a caesarean section."

The study found 66.9% of women who had a caesarean went on to have another pregnancy, against 71.6% who had instrumental vaginal delivery and 73.9% who had a spontaneous vaginal birth.

The average length of time between pregnancies in the three groups was 36.3 months, 31.8 months and 30.4 months.

Women who had a caesarean were also more likely to have an ectopic pregnancy the next time, a dangerous complication where the fertilised egg becomes implanted outside the womb.