Establishing the safety of waterbirth for mothers and their babies: the POOL cohort study with nested qualitative component

Background
Intrapartum water immersion analgesia has been recommended by the National Institute for Health and Care Excellence since 2007, but high-quality evidence relating to the safety of waterbirth for mothers and their babies was lacking.

Primary study objective
To establish whether, in the case of ‘low-risk’ women who use water immersion during labour, waterbirth, compared to birth out of water, is as safe for mothers and their babies.

Methods
A cohort study with non-inferiority design.

Setting
Twenty-six National Health Service organisations in England and Wales.

Participants
The primary analysis included 60,402 births between January 2015 and June 2022. Primary analysis was restricted to births where the woman: (1) was without complicating medical conditions at the time of pool entry, (2) used water immersion during labour and (3) did not receive obstetric or anaesthetic interventions prior to birth. Comparisons were undertaken between women who gave birth in water and women who gave birth out of water.

Main outcome measures
Maternal primary outcome: obstetric anal sphincter injury (with planned subgroup analysis by parity); neonatal composite primary outcome: fetal or neonatal death (after the commencement of intrapartum care and prior to discharge home), neonatal unit admission with respiratory support or the administration of intravenous antibiotics within 48 hours of birth. Separate a priori sample size calculations were undertaken for the maternal and neonatal primary outcomes.

Results
After adjusting for differences in the characteristics of women who used intrapartum water immersion and gave birth in or out of water: (1) among nulliparous women, rates of recorded obstetric anal sphincter injury were no higher among women who gave birth in water than among women who left the pool before birth [730 of 15,176 women (4.8%) vs. 641 of 12,210 women (5.3%); adjusted odds ratio 0.97; one-sided 95% confidence interval, −∞ to 1.08]; (2) among parous women, rates of recorded obstetric anal sphincter injury were no higher among women who gave birth in water than among women who left the pool before birth [269 of 24,451 women (1.1%) vs. 144 of 8565 women (1.7%); adjusted odds ratio 0.64; −∞ to 0.78].

Among babies, rates of the primary outcome were no higher among babies born in water than among babies born out of water [263 of 9868 infants (2.7%) vs. 224 of 5078 infants (4.4%); adjusted odds ratio, 0.65; −∞ to 0.79].

All upper confidence intervals of the primary outcomes were lower than the prespecified margins of non-inferiority; therefore, we conclude that the rate of the primary outcomes for mothers and their babies were no higher among waterbirths than among births out of water.

Rates of the individual components of the neonatal primary outcome were: Intrapartum or neonatal death, which occurred in three babies born in water (0.3. per 1000 births) and zero in babies born out of water. Respiratory support on a neonatal unit was provided to 91 (0.9%) of babies born in water and to 104 (2.0%) of babies born out of water; (adjusted odds ratio 0.44, one-sided 95% confidence interval −∞ to 0.60). Antibiotics were administered within 48 hours of birth to 263 (2.7%) babies born in water and to 224 (4.4%) babies born out of water (adjusted odds ratio 0.65, −∞ to 0.79).

The online survey and interviews identified various factors influencing the use of birth pools in the United Kingdom and emphasised the need to address issues related to resource availability (including midwives with experience of waterbirth), unit culture and guidelines and staff endorsement. The site case studies found obstetric units less facilitating of waterbirth compared to midwifery units in relation to equipment and resources, staff attitudes and confidence, senior staff support and women’s awareness of water immersion.

Limitations
Limitations of the study included the inability to reliably identify women with medical or obstetric complications recorded in their medical records and the possibility of confounding between groups that were not known or could not be adjusted for – including reason for getting out of pool.

Conclusion
For women without pregnancy and labour complexities who use water immersion during labour, birth in water was as safe for mothers and their babies as birth out of water. This study supports policy and practice to enable women with an uncomplicated pregnancy and labour, who use intrapartum water immersion, to have the choice of remaining in, or leaving, the water to give birth.

Future work
Having established the safety of waterbirth for women and their babies, future work should concentrate on methods to reduce rates of severe perineal trauma during spontaneous vaginal births; support women to access water immersion during labour; improve understanding of the psychosocial impact of birth environments, including birth pools; increase understanding of the physiological impact of labour and birth in water; and measurement of blood loss in water.