Epidurals provide pain relief during labour. Find out how they affect birth

Childbirth hurts, and over the past 20 years, the epidural has been the most widely used technique for relieving the pain. It acts by bathing the nerves in the lower spine with local anaesthetic administered via a tiny tube. This is left in place throughout the labour, so it's possible to top it up.

The epidural is extremely effective and is employed in at least 30 to 40 per cent of all births. However, there are disadvantages to the traditional epidural: labour can be prolonged as the anaesthetic numbs sensation below the waist, and the woman experiences loss of muscle control and movement. Uterine stimulating drugs may also be administered to get things going, but their use can lead to further intervention.

The use of an epidural is also associated with increased rates of instrumental vaginal delivery, as the anaesthetic dulls the pushing contractions that stimulate the woman to expel the baby. So forceps (like tongs which gently cradle the baby's head and allow the doctor to ease it out) and ventouse (rather like a sink plunger used for the same purpose) are often used to assist the delivery.

These disadvantages led to the development of the mobile (or mobilising/ambulatory/walking) epidural. This fairly new technique, which delivers excellent pain relief even faster, also leaves some sensation in the legs, allowing you to move around the delivery room.

Just how much movement is hard to predict, as it depends on the individual. Some women find that they aren't mobile at all, and others can only move from the bed to a chair. Most will be able to walk around, sit in a chair, or even go to the lavatory rather than having to use a bedpan.

There may be a warm, tingling feeling in the legs, and you usually need a bit of help to move around. Just as with the standard, traditional form, the primary aim is still to relieve pain in labour. The drugs available for this have become much more effective than those used in the past. Moving around is of secondary importance.

• The mobile epidural is set up in the same way as a standard epidural. It may even be possible to switch from the mobile to the standard if this becomes necessary (for instance if you needed an emergency Caesarean). The difference between the two is in the combination of the drugs used. These are maximised for pain relief while limiting the loss of sensation in the legs.

• Mobile epidurals can be started at any time during labour (as long as three hours have elapsed if a strong analgesic/painkilling injection, such as Diamorphine or Pethidine, has been provided). They can be given in the first stage if the contractions become unmanageable - or even earlier if there is a fear, which some women do have, about being in pain.

• The difference between the two lies in the anaesthetic solution. A mobile epidural uses a very diluted concentration of a local anaesthetic (usually Bupivacaine) mixed with an opiate (an analgesic, like Fentanyl and/or Pethidine), which helps block pain without impairing the motor (muscle) function in the legs, or causing leg weakness or numbness. It's not compulsory to move around. Often the relief gained allows the woman to have a rest. The control can last for as long as it takes to deliver the baby. There is a continuous supply of medication, patient controlled, at the push of a button.

• Excellent pain relief

• A mobile epidural takes effect in three to five minutes and allows the woman to move her legs. The effects last approximately two hours

• Total bed rest is not necessary

• Being in an upright position tends to speed up the dilation of the cervix (neck of the womb), labour and delivery

• Assisted delivery (instrumental or medical) is less likely than with a standard epidural

• Minimal, or no, drug affects on the baby, so that foetal distress - often a consequence of standard epidurals - is much rarer

• Increased maternal satisfaction now that the optimal medication has been determined

Disadvantages:

• All the drawbacks that follow the standard, traditional epidural, including the occasional spinal headache - caused by getting the needle in the wrong place - which is only temporary, and easily treated

• The amount of movement may be very limited

• Many hospitals do not offer mobile epidurals; the midwife in charge of a particular patient will be able to supply this information