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The POOL study aims to establish the safety of waterbirth for mothers and babies, and is a cohort study with a nested qualitative component.

Women use a birth pool during labour for pain relief and some women choose to remain in the pool for the birth of their baby. It is estimated that up to 60,000 (9 in every 100) babies are born into water annually in the UK. Some people are concerned that babies being born into water may increase risks for mothers and babies. Although studies to date suggest waterbirths are safe for mothers and babies, to date there has not been a study large enough to show this for certain.

Research approach

The study will collect data on the births of all women from 26 UK maternity units between 2015-2022. It will determine how many women are using birth pools, how many women give birth in water and whether mothers or their babies come to any extra harm as a result of water birth.

The primary study objectives are to:

  1. Evaluate if waterbirth is associated with an increase in adverse infant outcomes or treatment, to include asphyxia, infection, respiratory difficulties, and mortality; or maternal morbidity, particularly complex perineal trauma (Obstetric Anal Sphincter Injuries (OASIS)) and haemorrhage.
  2. Assess the primary safety outcomes amongst the subgroups of nulliparous and parous women who were low risk at labour onset.
  3. Describe rates and treatment of haemorrhage for low-risk women who, following birth in water, deliver the placenta underwater. This will also be described for women who leave the water prior to delivery of the placenta.

The secondary study objectives will set pool use and waterbirth in the context of NHS care. The study will describe:

  1. The overall proportion and characteristics of women who use a pool for labour or birth, compared to those who do not use a pool.
  2. The characteristics of, and outcomes for, women with identified risk factors at labour onset, who use a pool during labour.
  3. The characteristics of, and outcomes for, women who develop labour complications who use a pool during labour.
  4. Factors associated with high and low rates of pool use in individual maternity units.

To detail the proportion of women who use a pool during labour and how their characteristics compare to women who did not use a pool we need data on a minimum of 600,000 women.

To address the maternal primary outcome; Obstetric Anal Sphincter Injuries (OASIS) we require data on 30,000 women to have used a birth pool in labour and meet the NICE criteria for being ‘low risk’, including 15,000 who remained in the pool for birth.

The neonatal primary outcome is a composite of ‘adverse infant outcomes or treatment’ to include: (a) any neonatal unit admission requiring respiratory support (b) antibiotic administration within 48 hours of birth (with or without culture proven infection); and (c) intrapartum stillbirth or all deaths prior to neonatal unit/postnatal ward discharge. To address this outcome, we require a smaller sample size of 16,200, including 8,100 babies born into water.

To do this without disturbing women in labour or just after birth the study will use information routinely collected as part of maternity records stored at hospitals in computerised systems. To keep women’s information confidential, the data stored in existing maternity information systems will have identifying information, such as names, addresses and NHS numbers removed before the information is sent to the research team in Cardiff for analysis. Women have the opportunity to opt-out of this research study. How women are informed about the study will vary by site but will include the use of leaflets posters, social media and study cards.


Many professionals and parents have strong opinions on waterbirth. Some are great advocates, who promote the potential benefits of water birth to women, whilst others remain concerned that women may be taking additional unnecessary risks by giving birth in water.

The diversity of opinions towards waterbirth makes it particularly important that the study team have representatives from all interested groups. The professionals on the study team include midwives, an obstetrician and a neonatologist as well as the experts needed to deliver this large complex study. The National Childbirth Trust (NCT) is the largest parenting organisation in the UK and have joined the study team as have the Royal College of Midwives.

Project details

For a detailed project description please read The POOL Study. Establishing the safety of waterbirth for mothers and babies: A cohort study with nested qualitative component.