Background and waterbirth in the National Health Service
Water immersion during labour and birth was first introduced into NHS care in the late 1980s1 as a method of non-pharmacological pain relief, and it has now become part of mainstream maternity care for women with uncomplicated pregnancies, particularly in midwifery-led units (MLUs) and at home births.
Water immersion during labour can be facilitated in most birth settings, and NHS maternity units usually have specialist birth pools that vary in design. All birth pools offer sufficient depth of warm water for the woman to immerse her abdomen when sitting and sufficient space for her to move and change position easily; some pools have additional features such as inbuilt lighting and thermoregulation functionality, while inflatable, portable pools, with disposable liners are available for home or hospital use. Women enter the warm water, usually once labour is established, and either remain in the pool to give birth or leave the pool prior to birth, either through choice or due to clinical concerns. For those who give birth in the pool, some remain there until after delivery of the placenta.
To support women having more choice and control over their care options during labour, in 1992, the House of Commons Health Committee (Winterton Report) recommended that hospitals should provide women with the use of a birth pool for labour ‘where this is practicable’,2 but at this time, the practice was uncommon. A 1993 survey estimated that annually around 2250 women gave birth in water in England and Wales, with an additional 1900 women using a pool during labour.3 Births in water increased over the next decade, with surveys of maternity care in England reporting rates of 4.8% in 20064 and 5.1% in 2010.5
A Cochrane review published in 20046 identified eight international trials of water immersion during the first stage of labour (N = 2939) and found that there was a statistically significant reduction in the use of epidural/spinal/paracervical analgesia/anaesthesia among women allocated to water immersion during the first stage of labour compared to those not allocated to water immersion [odds ratio (OR) 0.84, 95% confidence interval (CI) 0.71 to 0.99, four trials, N = 2406]. One small trial included in the review found that women who used water immersion during the first stage of labour reported statistically significantly less pain than those not labouring in water (40/59 vs. 55/61) (OR 0.23, 95% CI 0.08 to 0.63). Pooled data from other small trials included in the review found no detrimental effect on neonatal Apgar scores at 5 minutes (five trials N = 1834), rates of neonatal unit (NNU) admission (two trials N = 1511) or rates of neonatal infection (two trials N = 1262). Just one trial7 (N = 117) compared immersion during the second stage of labour, but it was too small to reach conclusions on the impact of birth in water for mothers or their babies.
Informed by the 2004 Cochrane review, in 2007,8 the National Institute for Health and Care Excellence (NICE) recommended that women should be offered water immersion during the first stage of labour due to its analgesic effectiveness but recommended that there was insufficient high-quality evidence to support or discourage birth in water.
Benefits for women of warm water immersion during labour or birth have been poorly explored, but studies suggest they extend beyond pain relief. A meta-synthesis9 included seven studies exploring experiences of women who had used water immersion during labour and/or birth. The review found that women described positive experiences of warm water immersion. The warmth provided comfort, the buoyancy facilitated women’s ease of movement and change of position, and the birth pool space provided a safe space in which women could relax and claim as their own.
The availability of waterbirth facilities in the UK further increased following publication of the Birthplace in England study in 2011,10 which found planning birth in MLUs was as safe for mothers and babies as planning birth in an OU. This led to an increase in the proportion of births in MLUs, which commonly have waterbirth facilities, to 14% between 2010 and 2016.11 In 2015, 9% of 20,631 postnatal women who responded to a Care Quality Commission survey had experienced a waterbirth.12 Based on 700,000 live births annually in England and Wales,13 and a 60% spontaneous vaginal birth (SVB) rate,14 these data suggested that up to 52,000 babies were being born into water annually.
Justification for the study
Despite the high numbers of babies born into water under NHS care, evidence of safety from randomised trials is lacking. Pilot and feasibility randomised trials of waterbirth have been undertaken,7,15 the largest of which was conducted in Australia, recruiting 1260 participants;16 but it concluded that a trial of sufficient size, powered to detect a difference in serious neonatal morbidity was unlikely to be feasible.
Several cohort studies have reported outcomes of births in water, but with either potential limited applicability to the UK setting,17 insufficient size to explore rare but important outcomes,18 or with inadequate methods to compare outcomes between women who give birth in water with a similar group who experience an uncomplicated pregnancy and labour but give birth out of water by choice rather than due to clinical need.19
The potential for waterbirth to cause harm to babies has been highlighted by early case reports of adverse neonatal outcomes, including neonatal water aspiration,20 infection21,22 and hyperthermia.23
Adverse neonatal outcomes resulting in perinatal deaths or survival of babies with cerebral palsy have devastating lifelong consequences for families and surviving children. They also have important economic implications to the NHS, with a daily tariff for neonatal intensive care at £181124 and settlements for cerebral palsy resulting from clinical negligence having expected values of £10M.25 Case reports of adverse neonatal outcomes following, and often attributed to birth in water,26 have continued, and despite studies suggesting no increase in rates of adverse neonatal outcomes,17,18 widespread scepticism remains particularly among neonatal and paediatric healthcare professionals in the UK and internationally about the safety to babies of birth in water.
Clinical concern also remains around the potential of waterbirth to be associated with increased rates of severe perineal trauma.27 Rates of identified severe perineal trauma, involving the anal sphincter, among women giving birth vaginally to their first baby in England between 2000 and 2012 tripled from 1.8% to 5.9%.28 Although it is recognised, the increase probably reflects improved detection, and reporting28 reducing obstetric anal sphincter injury (OASI) is important as it is associated with faecal incontinence, dignity loss, psychosexual morbidity and a compromised role as a mother.29 It has been suggested that birth in water may be associated with increased rates of severe perineal trauma due to the inability of midwives to implement physical perineal protection27 as recommended by the Royal College of Obstetricians and Gynaecologists.30
The recently published 2023 update of NICE guidance for care of women in labour stated there continues to be insufficient high-level evidence to inform whether women who use water immersion during labour should be advised to leave, or remain in, the pool for birth.31 It is this gap in knowledge that the POOL Study was designed to address.
Study objectives
The primary study objective was to establish whether, in the case of ‘low-risk’ women who use a pool during labour, waterbirth, is as safe for mothers and infants as birth out of water.
The secondary objectives of the study were to:
- Evaluate if waterbirth was associated with an increase in adverse infant outcomes or treatment, including asphyxia, infection, respiratory difficulties and mortality; or maternal morbidity, particularly complex perineal trauma (OASIs) and haemorrhage.
- Assess the primary safety outcomes among the subgroups of nulliparous and parous women who were at ‘low risk’ at labour onset.
- Describe rates and treatment of haemorrhage for ‘low-risk’ women who, following birth in water, deliver the placenta underwater. This was also described for women who leave the water prior to delivery of the placenta.
The study also planned to:
- describe the proportion and characteristics of women who used a pool for labour or birth compared to women who do not use a pool
- describe the characteristics of, and outcomes for, women with identified risk factors at labour onset, who used a pool during labour
- describe the characteristics of and outcomes for women who develop labour complications, who used a pool during labour, inclusive of labour interventions such as cardiotocograph (CTG) and augmentaion with oxytocin.
- explore factors associated with high and low rates of pool use in individual maternity units.