Delivering in or out of water, the OASI rates in the POOL cohort
study are disturbingly high
Dear Dr Papageorghiou,
We have read with interest the POOL study report by Sanders et al.
published in your journal.1 We acknowledge that the
results of this study are based on a large obstetric cohort of low-risk
women.
The mere conclusion of the authors is that birth in water is not
associated with increased risks for mothers and babies. However, in
doing so, they seem to have overlooked an important issue related to the
event rate in their comparator group. Indeed, the reported obstetric
anal sphincter injury (OASI) rates of 5.0% in nulliparous and 1.3% in
multiparous women are remarkably, if not unacceptably high.
Particularly, given the risk for serious, often untreatable
complications strongly associated with such injury.
The reported event rates in the pool study are an outlier when compared
to the 1.6% reported in other studies.3 The reported
rates in the POOL study are comparable to those reported by
Gurol-Urganci et al.4 Nonetheless, 20% of the women
in the Gurol-Urganci et al study had operative vaginal births, a strong
risk factor for OASI. In contrast, the POOL study cohort were all
low-risk spontaneous births.
The POOL study describes women delivering in and out of water, but the
authors do not comment if manual perineal protection was used or not in
either of the groups. Applying interventions, like manual perineal
protection at the time of water birth may be challenging and does not
tend to be attempted in some healthcare settings.
Manual perineal protection was earlier associated with a significant
reduction in OASI risk in Norway and Denmark and the UK. Fodstad et al.
describe that the OASI prevalence in Norway in all vaginal deliveries
has reduced from 4.2% in 2004 to 1.6% in 2023, after introduction of a
national program with manual perineal protection.3
Gurol-Urganci et al. have also demonstrated a significant reduction OASI
rates in a healthcare setting comparable to that of Saunders et al.
Moreover, the RCOG and, more recently, the published report from the
All-Party Parliamentary Group on Birth Trauma have recommended the roll
out and implementation, underpinned by sufficient training, of the OASI
care bundle to all hospital trusts to reduce risk of perineal injuries
in childbirth.4 Hence, it would have been expected
that a UK based study using perineal trauma as its primary outcome would
address and discuss what interventions were undertaken to mitigate the
risk of trauma.
We believe that there is a high risk that the exceptionally high OASI
rate in the comparator arm has introduced bias in this non-inferiority
RCT. Sanders et al conclude that their “Study findings provide
reassurance that birth in water, in the context of UK midwifery
practice, is not associated with increased risks for mothers or their
babies. However, given the 2015 Supreme Court Montgomery ruling stating
that “clinicians should disclose risks of childbirth” one should
question, why the risk of childbirth in the POOL study was so
unacceptably high and still remained undiscussed?
Jan Willem de Leeuw, Department of Obstetrics and Gynaecology, Ikazia
Ziekenhuis Rotterdam, the Netherlands
Katariina Laine, Norwegian Research Centre for Women’s Health, Oslo
University Hospital, Oslo, Norway, Institute of Clinical Medicine,
Faculty of Medicine, University of Oslo, Oslo, Norway
Margareta Manresa, Clinic Institute of Gynaecology, Obstetrics and
Neonatology, Hospital Clinic of Barcelona, Barcelona, Spain
Sari Raisanen, Laurea University of Applied Sciences, Vantaa, Finland
Vladimir Kalis, Department of Obstetrics and Gynaecology, Faculty of
Medicine in Pilsen, Charles University, Center for Pelvic-floor
Disorders, Pilsen, Czechia
Zdenĕk Rušavý, Department of Obstetrics and Gynaecology, Faculty of
Medicine in Pilsen, Charles University
Renaud de Tayrac, Obstetrics and Gynaecology Department, Nimes
University Hospital, University of Montpellier, Nimes, France