Scientists have found that low-dose alternatives may be safer.

Epidurals are the most effective form of pain relief during childbirth.

An injection of local anaesthetic is administered to numb the lower back and is then fed continuously via a thin plastic tube into the epidural space between the spinal cord and spinal vertebrae.

However, conventional epidurals increase the likelihood that doctors will have to use forceps or other instruments to help the woman give birth - raising the risk of complications.

This compared to just 35% of those given a conventional epidural.

Possible risks

However, babies whose mothers were given a low-dose epidural took longer to become vigorous after delivery, and a few of the babies in the low-dose infusion group were more likely to require breathing assistance.

Writing in The Lancet medical journal, the researchers, Andrew Shennan and Christine MacArthur, from St Thomas' Hospital, say that their work has demonstrated that low-dose epidurals have "clear advantages" over the conventional technique.

"Long-term data are not available yet, but in relation to delivery outcome, continued routine use of traditional epidurals might not be justified."

In an accompanying commentary, James Thornton from the University of Leeds said: "The message from this study is clear.

Pain control

"Anaesthetists should offer the technique that interferes least with the normal mechanisms of labour, namely either combined spinal epidural or low-dose infusion epidural.

"These methods offer the best chance of a spontaneous delivery with satisfactory pain control.

"If the traditional technique is used, women should be informed that they are associated with an increased risk of operative vaginal delivery."

The research is published in The Lancet medical journal.