Sterile water injections

What is a sterile water injection?

Sterile water injections are also known as sterile water blocks. They are used to manage back pain in labour or ‘back labour’ by injecting medical-grade sterile water just under the skin on the lower back. Most evidence suggests they do not help the pain caused by contractions (Märtensson et al, 2008).

What is back labour?

During labour, most women and birthing people experience contractions that come and go, with a short break in between. Around one in three experience constant lower back pain, as well as contractions. This can happen when the baby’s head presses down on the nerves in the pelvis (Oxford University Hospital Trust, 2024; Wickham, 2024).

By reducing back pain, sterile water injections can give women and birthing people some rest and help them better cope with labour pain (Oxford University Hospital Trust, 2024).

A woman or birthing person may also want to try moving into different positions during labour. For example, kneeling or getting on all fours can help to ease back pain and encourage the baby to move (NHS Newcastle, 2025).

Who can have a sterile water injection?

Any woman or birthing person can request a sterile water injection during labour.

Where can you get a sterile water injection?

It’s possible to use sterile water injections in all birth settings, including hospital labour wards, midwife-led units, and when giving birth at home (Lee et al, 2020; NICE, 2023).

They must be given by a trained midwife or doctor, and this may limit availability in some areas.

Not all NHS Trusts offer sterile water injections, so it’s a good idea to ask about this during pregnancy.

How are sterile water injections given?

A sterile water injection is given using a small syringe. Four injections are given in four locations under the skin on the lower back (Wickham, 2024).

They can be given during a contraction to distract from the sting. Gas and air (Enotox) can also be used at this time if needed (Oxford University Hospital Trust, 2024).

Back pain may ease within 10 minutes, and relief can last up to three hours (NICE, 2023). Injections can be given as frequently as needed (Oxford University Hospital Trust, 2024).

How do the sterile water injections work?

Sterile water injections create a strong stinging sensation (NICE, 2023). This triggers the body’s natural pain-relieving hormones (endorphins) to manage the pain of the injection. This can reduce back pain at the same time (Oxford University Hospital Trust, 2024).

While contraction pain continues to come and go, back pain is eased.

Are sterile water injections effective?

Studies show sterile water injections can help to reduce back pain during labour for many women and birthing people.

In one study about half of the women who had the injections felt their back pain lessen for up to 90 minutes (NICE, 2023; Oxford University Hospital Trust, 2024; Lee et al, 2020).

In other research twice as many women who received the sterile water injections said their pain was reduced by half within 30 minutes, compared with those given a placebo. Many women rated the injections as very effective for up to 90 minutes (Lee et al, 2020).

Women also describe using this time to rest or focus more on their birth experience (Lee et al, 2017).

Some emerging research suggests sterile water injections in the abdomen may also help reduce contraction pain for a short time (Lee et al, 2026), but these studies are new and will take time to be used in maternity services.

What are the benefits of Sterile Water Injections?

In addition to easing back pain, sterile water injections (Oxford University Hospital Trust, 2024; Wickham, 2024):

• Often work immediately
• Don’t affect alertness or awareness
• Have no side effects for the baby
• Don’t cause allergic reactions
• Can be repeated as much as needed
• Can be used with other pain management options, including water birth
• Don’t affect movement, pushing, or feeling sensations during birth
• Are suitable in all birth settings

Are there any side effects?

There are no side effects for women or birthing people, other than the sting of the injection (Lee et al, 2026). They do not increase the risk of unplanned caesarean birth, vaginal birth with forceps or ventouse, or neonatal unit admission (Lee et al, 2020; NICE, 2023).

As with any injection, there is a very small chance of infection or inflammation where the injection is given (Wickham, 2024), though no cases have been recorded in the research studies (NICE, 2023).

Other things to consider before using sterile water injections

• At the time they are given, the injections are painful, which can deter some people (Oxford University Hospital Trust, 2024; Lee et al, 2022; Wickham, 2024).
• For a small number of women (5 to 15 in 100) they may not work (Oxford University Hospital Trust, 2024).
• Most evidence suggests they should be used to relieve back pain only, not contraction pain (Lee et al, 2026).
• They must be given by a trained professional, which may limit access in some local areas. They are not available in every NHS Trust.
• Evidence is still emerging, so there is limited clinical guidance available (NICE, 2023), which could impact availability. Expectant parents who are interested in this option should speak to their midwife during pregnancy.

What other pain management options are available?

To learn about other pain management options read our articles on:

• Using a TENS machine
• Gas and air (Enotox)
• Epidurals
• Intramuscular opioids (Pethidine/ Diamorphine)
• Remifentanil

Need more information?

Every woman and birthing person has the right to feel safe, informed, supported, and confident about their decisions.

For further information, we offer NCT antenatal courses which are a great way to prepare for pregnancy, birth, and life with a new baby.

Our NCT support line also offers practical and emotional support with feeding your baby and general enquiries for parents, members and volunteers: 0300 330 0700.