We wanted to see how interventions like analgesia affect a new-born's behaviour

Professor Anna-Berit Ransjo-Arvidson, of the Karolinska Institute, in Stockholm

The research, published in New Scientist, says that this in turn may affect levels of a key maternal hormone that helps mother and baby bond shortly after birth.

Professor Anna-Berit Ransjo-Arvidson, of the Karolinska Institute, in Stockholm, said researchers knew analgesics taken during labour have adverse effects on the mother.

But she said that the effects on the baby were not well documented.

In earlier studies she and her colleagues found that new-borns whose mothers took no painkillers during labour instinctively moved towards the mother's breast, massaged it with their hands, reached for the nipple and started suckling just an hour after birth.

Breast feeding

Professor Ransjo-Arvidson said: "We wanted to see how interventions like analgesia affect a new-born's behaviour."

She and her team video-taped 28 new-born babies who were delivered vaginally.

They were dried and placed on their mother's breast.

Eighteen of the mothers had taken some form of painkiller including bupivacaine, mepivacaine and pethidine.

The 10 babies not exposed to the pain killers fed normally - the others did not massage the breast at all, or rarely.

And nearly half of them did not breast feed within the first 2.5 hours after birth.

Professor Ransjo-Arvidson said she thought the painkillers were numbing the babies.

Among the women who took no pain killers the team also found levels of the hormone oxytocin, which controls lactation and contraction of the uterus.

Her team is now starting to study this connection.

Sample

She said: "We need to do more studies, especially as there is a very high increase in the use of epidural and other pain relievers.

"But analgesics are big business and it won't be easy to convince hospitals to forgo painkillers, despite their drawbacks. There is a lot of money in epidurals."

A spokeswoman for the Royal College of Midwives said that it was difficult to make any observations on the study because it is a small sample.

But they said they were aware of some problems following certain pain killers.

"We have known for years that pethidine does make babies sleepy after birth, and that can delay breast feeding."

A spokeswoman for the National Child Birth Trust said the report highlights the problems with pain killers during birth.

"This research points up the value of non-medical forms of pain relief in labour, in particular the continuous support of a midwife, the chance to give birth in familiar, non-threatening surroundings, access to a birth pool, massage and space to move around in.

"Women who are informed, relaxed and more in control of their birth experience tend to rely less on pain relief during labour."