I have recently been asked to research (and potentially implement) a technique in which the midwife injects four small quantities of sterile water into the lower back of the labouring mother. This is something I was unfamiliar with and I was set on a path of discovery. I have learned that the practice is known and offered to women in labour by midwives all over the globe. Units from Australia, New Zealand, California, Scandinavia, as well as some from the UK, have responded to my query to say that this is part of their practice.
Sterile water injections (SWI), administered by midwives, are a simple and well-established method of managing labour pain. This intervention was first used to alleviate pain associated with kidney stones and was introduced to obstetrics in the 1970s. Using a syringe, small amounts of sterile water are deposited intradermally near the sacral area. The sterile water causes osmotic and mechanical irritation resulting in a brief stinging sensation, lasting for 15–30 seconds. The onset of pain relief follows almost immediately and can last for up to two hours. The procedure can be repeated many times. In labour, the injections are administered sequentially during a contraction, with the series of four injections, performed two at a time, completed within 20–30 seconds.
The more I read about the research findings online, the more I think the technique has to be seen in practice to get a true sense of the help and comfort it can offer women. Much, but not all, of the research published is ambivalent about the impact, whereas the feedback from midwives is that the injections are a brilliant tool to support mothers to have drug-free births, and to avoid a cascade of interventions, and the trauma that accompanies them. They also allow women to stay upright and mobile to maximise the chance of using gravity to facilitate the birth.
Midwife Caroline Hastie explains how the injections work in an article published on the website bellybelly:
“The concept behind the development of sterile water injections for pain is ‘gate control theory’. Our skin has thousands of receptor sites and nerve cell endings. They scan for pain, pressure, touch etc, and can transmit that information to the brain very quickly. Sensations shoot up the nerves and spinal cord to the brain. The sensations (which are chemical and electrical signals) go through little traffic control stations. The signal boxes in the nerve pathways are ‘manned’ by chemical signallers which let pain, pressure, touch signals through to the brain. The signal boxes in the nerve pathways are called gates because they choose which signal to let through. When the brain receives the signals, it decides what action to take. The traffic controllers (chemicals) that man the gates preference skin signals over internal signals. This is because the skin is monitoring the outside environment, and it lets the brain know when there is immediate danger. When a woman has back pain in labour, the pain signals are slow, internally generated signals. If a woman has the water injections into her skin, it stings for about thirty seconds. That sting switches on the fast fibres. The fast fibre signals from the skin come racing up to the gate. The traffic controlling chemicals recognise an immediate threat, close the gate to the slow pain messages, and let the quick skin-related message through. The internal pain signal is stopped in its tracks, and the woman no longer feels that internal sensation. That effect lasts for about 90 minutes.”1
The risks with sterile water injections are very low since no pharmaceutical medication is used with the technique and the injections are made just beneath the skin. The nerve points where the sterile water is injected are known nerve receptors for pain experienced in the back, uterus, cervix and pelvic floor. Most types of pain encountered in labour can therefore be relieved to a degree by sterile water injections, though the technique is most effective in relieving back pain. In a study by the University of Queensland, twice the number of women given sterile water injections reported significant pain relief compared to a placebo group.2
The findings are fantastic and, like the rebozo, sterile water injections offer support and help to women without resorting to the drug route, which leaves a legacy. The next step for me is to receive some formal training. I can then look into offering a service and training colleagues so we can expand our repertoire of support tools, and be more helpful to more mothers, more of the time.
Eleanor Copp supports families across the UK, currently online. relaxedparenting.co.uk 07929 857 608
- Kelly Winder, ‘Sterile water injections for back pain in labour’, (24 December 2020) available at bellybelly.com.au/birth/sterile-water-injections.
- ‘Water injections could be used to relieve labour pains’, UQ News (16 June 2021), available from the University of Queensland website tinyurl.com/yeaovpqq.
First published in Issue 77 of JUNO. Accurate at the time this issue went to print.