"Healthy" obese women, who have given birth to a baby before, are at lesser risk than first-time mums of normal weight, according to a new study.

But a new study by Oxford University shows the risks are not the same for all obese women.

Lead researcher Dr Jennifer Hollowell of the National Perinatal Epidemiology Unit at Oxford University, said that the increased risk was fairly modest for obese women who did not have conditions like high blood pressure, diabetes or a previous caesarean section, and the risks were quite low if the woman had given birth previously.

She said that they found that around half of very obese women giving birth in obstetric units have medical problems or pregnancy complications when admitted.

Hollowell asserted that their study focused on women who were obese but otherwise healthy when they went into labour, and some of them had much lower risks than might have been expected.

The Oxford University researchers point out that, among healthy women with a straightforward pregnancy, childbirth risks are influenced more by whether someone is a first-time mum than whether they are obese.

They found that the chances of first-time mums of normal weight having medical interventions or complications during childbirth are greater than for `very obese` but otherwise healthy women having a second or subsequent child. The findings are published in the British Journal of Obstetrics and Gynaecology.

The findings have been published in the British Journal of Obstetrics and Gynaecology.