How four jabs of sterile water can ease pain during labour

Giving pregnant women an injection of sterile water into their lower back has been shown to ease pain during childbirth.

A teaspoonful of water is injected just under the skin, at four points around the bottom of the spine, when there is severe backache.

New research suggests the jabs significantly reduce back pain for all the women who have them, and can provide relief for several hours. The water causes the injection points to sting slightly, and this is thought to interrupt the transmission of pain signals from the spine to the brain.

The severe back pain, which affects around a third of women during labour, is caused by the baby’s head stretching the tissues and nerves in the pelvis as it moves through the birth canal. 

Those pain signals travel to the brain via nerves that run close to the surface of the skin near the lower end of the back, causing a severe ache there.

For some women, the discomfort is so bad that they opt for powerful pain relief such as an epidural, where a thin tube is inserted into the spine and local anaesthetic is gradually fed through it.

But epidurals must be done by specialist anaesthetists as there is a risk of damage to nerves and temporary effects such as loss of bladder control, a drop in blood pressure or — more rarely — lasting injury, with an estimated one in 50,000 mothers suffering permanent loss of feeling in one or both legs.

Sterile water injections, which can be given by midwives, could be an effective alternative that is safer and cheaper.

The technique has been used in other countries such as Sweden, Canada and Australia for decades. But it has been much slower to take off in the UK, with very few maternity units offering it.

This is partly because the National Institute for Health and Care Excellence (NICE), which vets new treatments, has ruled there is insufficient evidence to support its use.

However, that could change after a recent landmark study by Oxford University and the University of Queensland in Australia found water injections are highly effective, easy to administer and — crucially — have no adverse effects on babies or their mothers.

The five-year study, published in the journal EClinicalMedicine, compared the results of 580 women given sterile water injections with another group given salt water (or saline) injections.

This salt water is isotonic, which means it has a similar ratio of salt and water to the fluids found inside most of the body’s cells. As a result, once injected beneath the skin, it tends to be rapidly absorbed by the cells.

Sterile water is non-isotonic, which means it is much less likely to be absorbed and remains in place for longer when it is injected under the skin.

While both types of water were found to ease back pain, the benefits from salt water lasted just minutes before it was absorbed, while the benefits from the sterile water often lasted for 90 minutes or longer.

When water is injected into the lower back, it irritates the same nerves that are triggering the backache.

This diverts the nerves’ attention away from the back pain, and they send signals to the brain about the mild stinging caused by the water instead. 

Even though the stinging only lasts for about 30 seconds, the block on back pain signals caused by sterile water can last for up to three hours.

Professor Sally Collins, a consultant obstetrician who was part of the research, said: ‘Many other countries use this simple pain-relieving technique. But the evidence that it works was sadly lacking, so many healthcare professionals dismissed it as nonsense.

‘However, with this robust new evidence we are anticipating that NICE will review its guidance. Sterile water only costs a few pence and the treatment is going to make a huge difference for a great many women.’

Professor Hasib Ahmed, a consultant obstetrician and gynaecologist at Medway NHS Foundation Trust in Kent, said: ‘Some doctors dismiss this as witchcraft, but it’s hard to ignore the fact that it works.

‘At our hospital we routinely offer it to our patients, and midwives are trained to know exactly where to inject the water.

‘This latest study is a well-designed and robust bit of research and provides the evidence we need to support its use.’