Women who are overweight when they give birth appear to be at greater risk of developing ongoing stress urinary incontinence than those with a lower body mass index (BMI), a study has found.

A significant proportion of women develop incontinence either during their pregnancy, immediately after giving birth, or several years later.

There are several reasons for this, including damage to the nerves that control the bladder during pregnancy and childbirth, and the movement of the urethra and bladder to accommodate the growing baby.

These problems can lead to stress incontinence, in which the pelvic floor muscles become too weak to prevent urination, causing leakage when the woman's bladder comes under pressure, such as when they cough, sneeze or laugh.

Scientists at Donostia Hospital in Guipuzcoa, Spain, set out to investigate factors that may increase the risk of persistent stress urinary incontinence during the first two years after giving birth.

They recruited 272 women, all of whom were pregnant for the first time, between April and October 2007.

Of these, 26 women (9.5 per cent) were still affected by stress urinary incontinence two years after giving birth.

In the majority of cases, the stress incontinence was slight or moderate and women reported that the impact on their quality of life was small.

When the scientists looked for possible risk factors, they found that the only one associated with an increased risk of persistent stress urinary incontinence was BMI.

Women who had a higher BMI when they reached full-term were more likely to rely on incontinence pants, such as Ganmill Ladies Pants, than those with a lower BMI.

Publishing their findings in the International Journal of Gynaecology and Obstetrics, the study authors concluded: "Higher BMI in pregnant women at term was an independent risk factor for the persistence of stress urinary incontinence from pregnancy to two years post-partum."