Waterbirth: What Is the POOL Study Trying to Find Out?

Warm water immersion during labour is widely used in UK maternity care. Many women describe it as calming and helpful for pain relief, and NICE guidance has recommended offering water immersion for women without pregnancy risk factors since 2007.

But a common question remains: if labour is progressing normally and everything stays low risk, is it as safe to stay in the pool to give birth, or is it safer to get out for the birth itself?

A large UK study called the POOL Study set out to answer exactly that.

What was the POOL Study?

The POOL Study was a UK cohort study across 26 NHS maternity services. It looked at women who were already using water immersion during labour and who had no antenatal or intrapartum risk factors under NICE guidance.

The researchers compared outcomes for:

Women who stayed in the water and gave birth in the pool (waterbirth)
versus
Women who laboured in water but left the pool before giving birth (birth out of water)

Importantly, this comparison was limited to women whose births remained uncomplicated and who did not receive obstetric or anaesthetic interventions before birth (for example, operative birth, continuous fetal monitoring, epidural, or oxytocin augmentation). This was done so the groups being compared were as similar as possible.

Because this was an observational study rather than a randomised trial, the researchers used statistical methods to adjust for differences between groups, such as maternal age, parity, ethnicity, deprivation, BMI, gestational age and birthweight.

Who was included?

Between 1 January 2015 and 30 June 2022, the study identified 87,040 women who used water immersion during labour across participating sites. For the main analysis, the researchers focused on 60,402 women whose pregnancies and labours remained low risk and who did not have obstetric or anaesthetic interventions before birth.

Within this group:

39,627 had a waterbirth (65.6%)

20,775 left the water before birth (34.4%)

The study also noted that women living in more affluent areas were more likely to have a waterbirth than women living in more deprived areas, highlighting an important equity issue around access to choices in labour.

What outcomes did the study look at?

The study focused on two primary outcomes.

For mothers, the primary outcome was severe perineal trauma: obstetric anal sphincter injury (OASI). This includes third- and fourth-degree tears.

For babies, the primary outcome was a composite measure of serious early outcomes or treatments, including:

stillbirth after labour care had started or neonatal death before discharge
neonatal unit admission requiring respiratory support
intravenous antibiotics started within 48 hours of birth

This composite measure was designed to capture outcomes that have historically raised concern in case reports of waterbirth, such as breathing difficulties or infection.

What did the study find?

Overall, the study found that among women using water immersion in uncomplicated labour, giving birth in water was not associated with higher rates of the primary adverse outcomes for mothers or babies compared with leaving the pool before birth.

Maternal outcome: severe tears (OASI)

Among women giving birth for the first time (nulliparous):

OASI occurred in 4.8% of waterbirths (730 out of 15,176)
OASI occurred in 5.3% of births out of water (641 out of 12,210)

After adjusting for relevant factors, the study concluded there was no evidence of a higher rate of OASI in the waterbirth group.

Among women who had given birth before (parous):

OASI occurred in 1.1% of waterbirths (269 out of 24,451)
OASI occurred in 1.7% of births out of water (144 out of 8,565)

Again, there was no evidence of increased OASI risk for waterbirth in this low-risk group, and the study reported a lower rate among parous women in the waterbirth group.

Neonatal outcome: serious early complications or treatment

For babies, the composite primary outcome occurred in:

2.7% of waterbirths (263 out of 9,868)
4.4% of births out of water (224 out of 5,078)

In other words, serious early neonatal outcomes or treatments were not higher in the waterbirth group in this study population.

A key nuance: snapped umbilical cord

One notable finding was that “snapped umbilical cord before clamping” (sometimes called cord avulsion) was more common among waterbirths:

1.0% in waterbirths
0.3% in births out of water

Although this outcome remained uncommon, the difference was clear. The study also reported that when cord snapping occurred, babies had higher rates of neonatal unit admission and early antibiotics compared with babies whose cords were clamped before cutting. No babies with a snapped cord died, and none required therapeutic hypothermia in this analysis.

This is an important practical point because it relates to technique, handling, and training around lifting the baby to the surface and cord management during waterbirth.

What does this mean for parents?

If you are low risk, plan to use water immersion during labour, and labour remains uncomplicated, this study provides reassurance that staying in the pool to give birth was not linked with higher rates of severe tears or serious early neonatal complications compared with getting out for birth.

It also highlights an important question to ask your maternity team if you are considering waterbirth:

How does the unit manage cord handling and training to reduce the risk of cord snapping during waterbirth?

It’s also worth remembering that many women leave the pool before birth for a range of reasons, including personal preference, fatigue, changes in comfort, or to access other forms of pain relief or monitoring. Leaving the pool is not a “failure”; it’s simply one of the options available as labour unfolds.

What does this mean for healthcare professionals?

The POOL Study is one of the largest UK analyses of outcomes following intrapartum water immersion and waterbirth, focused specifically on women without antenatal or intrapartum risk factors and without obstetric or anaesthetic interventions before birth.

The results support counselling that, within this group and within NHS midwifery-led practice, waterbirth is not associated with increased incidence of the primary maternal and neonatal adverse outcomes measured.

The finding of increased cord snapping in waterbirth, although uncommon, is clinically relevant and supports continued emphasis on training, technique and local guidance around managing the baby’s emergence and cord handling during waterbirth.

Strengths and limitations

Strengths

Large sample size across 26 UK NHS maternity services
Focused comparison between women who all used water immersion in labour
Use of routinely collected NHS data and linkage with neonatal datasets
Adjustment for multiple factors that can influence outcomes

Limitations

Observational (not randomised), so unmeasured confounding may remain
Some missing data in certain fields and variations between sites
Very rare outcomes remain difficult to study even with large datasets
Findings are most applicable to settings with similar UK NHS midwifery practice

Bottom line

In this large UK study of low-risk women who used water immersion during uncomplicated labour, giving birth in water was not associated with an increase in severe perineal tears or serious early neonatal complications compared with leaving the pool before birth.

One outcome, snapped umbilical cord before clamping, was more common in waterbirths, though still rare, and is an important point for maternity teams and parents to discuss when planning care.

If you’re considering water immersion or waterbirth, speak with your midwife about what’s available in your unit, how they support waterbirth safely, and what factors might influence decisions during labour