The truth about ... pethidine

For those who believe that in the hours before childbirth a woman needs all the (chemical) help she can get, things are looking bleak. Pethidine, a drug widely used during labour and second only in popularity to gas and air, is totally ineffective as a pain-killer, according to a recent commentary in The Lancet.

Felicity Reynolds, emeritus professor of obstetric anaesthesia at St Thomas's Hospital, London, says that women are being conned into having pethidine in the belief that it will numb the pain, when in reality it only sedates them. She is calling for an end to its use in labour, arguing that women should instead be offered the new, safer lower-dose epidurals. Pethidine, she believes, is only given by midwives because it is cheap and means women "make less fuss".

So is she right?

A synthetic narcotic derived from morphine , pethidine is one of the strongest analgesics known, and is widely used to relieve pain after surgery Given by intramuscular injection, it takes effect within about 20 minutes and lasts between two and four hours.

But despite its effectiveness for other types of pain, pethidine is not an ideal analgesic for the intermittent, very severe pains of labour. Because it enters the bloodstream, it cannot be used in doses high enough to prevent the intensity of pain - if it was, the woman would be out cold and the baby would be at serious risk.

Although some studies have found that pethidine is effective during labour, they are either based on reports from observers rather than from the women themselves, or the women have been interviewed 24 hours after the birth - by which time the euphoria of having a new baby has often blocked out the experience which preceded it.

A recent, rather small study from Sweden, published in the British Journal of Obstetrics and Gynaecology, which evaluated the effect of both pethidine and morphine during labour, actually interviewed women while they were having their contractions. It found that neither drug reduced pain scores, and that both left some women heavily sedated.

Pethidine has other drawbacks: it can make a woman feel disoriented, nauseous and out of control, or leave her so sedated that she has few memories of the actual birth. The drug also increases the amount of time undigested food remains in the stomach, which can cause problems if a woman later has to have an anaesthetic.

In addition, pethidine readily crosses the placenta; if the drug is given too near the time of delivery, it can delay breathing at birth, make feeding difficult and cause the baby to be very drowsy. There is an antidote available, naloxone, which can be injected into the umbilical vein at birth, but it is not always given.

On the plus side, some women report a sense of euphoria from pethidine. The drug can reduce anxiety, and although it may not directly reduce pain, it is thought to increase pain tolerance. It can be particularly useful in helping a woman who is going through false or pre-labour - in which contractions can continue for days without the cervix dilating - to get some sleep. Most professionals would say that, despite its drawbacks, pethidine does have a place - albeit a limited one - in labour, but that women should be fully informed of its possible effects.

There is, after all, no ideal analgesic for childbirth: gas and air, or Entonox, can cause nausea and wooziness, while epidurals aren't totally free from risk, nor always available.

Anyone who does opt for pethidine in labour should ensure that the dilatation of the cervix is checked before it is given, to avoid ill-effects during delivery and on the baby afterwardsn