Which vaginal birth method, water or bed delivery, decreases the risk for obstetric anal sphincter injuries (OASIS)? Is immersion in water a good idea to prevent OASIS?

Zachariah R1, Forst S1, Geissbühler V2

Research Type


Abstract Category

Anorectal / Bowel Dysfunction

Abstract 22
Live Urogynaecology, Female & Functional Urology - Childbirth and its Consequences
Scientific Podium Session 3
Friday 15th October 2021
08:00 - 08:10
Live Room 1
Pelvic Floor Female Anal Incontinence
1. Kantonsspital Winterthur, Switzerland, 2. Claraspital Basel, Switzerland

Rebecca Rachel Zachariah



Hypothesis / aims of study
Water delivery has become a popular alternative birthing method with objective and subjective advantages, such as less episiotomies, less use of analgetics and a better birthing experience. Interpretations of existing data vary widely (1) (2). Perineal injuries and their prevention are a big issue in the context of vaginal deliveries. In particular, obstetric anal sphincter injuries (OASIS) are feared, because of the increased risk of fecal incontinence, perineal pain and dyspareunia, which may persist and reduce quality of life. Primiparae are known to have the highest risk for OASIS.
The use of warm compresses on the perineum in the second stage of labor reduces the rate of OASIS. Immersion and delivery in water might have a similar effect on the perineum by providing pressure relief. Data concerning the risk of OASIS in water are controversial (3). 
The aim of this study is to compare OASIS after water and bed delivery by primiparae.
Our hypothesis: primiparae, with identical management, have the same rates of OASIS after water and bed delivery.
Study design, materials and methods
The cohort group of 3907 primiparae gave birth in water or on the bed between 1991 and 2006 in a public teaching hospital.
Inclusion criteria: primiparae, ≥ 37 0/7 weeks of gestation, cephalic presentation, waterbirth with complete delivery of the baby under water and landbirth with delivery on bed, both with primiparae in a slight upright position on their back.
Exclusion criteria: preterm birth < 37 0/7 weeks of gestation, epidural anesthesia, instrumental deliveries.
The management of water- and bedbirths by the medical staff was identical, e.g., fetal heart rate monitoring, intermittently in the first stage and continuously in the second stage of labor, indication for use of oxytocin or episiotomies. A midwife or an obstetrician protected the perineum by the “hands on” technique: one hand supports the fetal occiput and the other hand applies slight pressure on the perineum to control the delivery of the fetal head. The diagnosis of a perineal tear and OASIS was made by consultants in obstetrics and gynecology and afterwards treated by them. 
All deliveries were documented by a specially designed questionnaire. 
The following parameters were considered: Maternal age, duration of delivery, duration of second stage of labor, use of oxytocin, fetal birth weight, rate of episiotomies.
In this exploratory study we compared the rate of OASIS in the water delivery group and the bed delivery group. 
Subgroup analyses explored the rate of OASIS in water or bed correlated to the birth weight, the duration of the delivery, the duration of the second stage of labor, the rate of episiotomies and the use of oxytocin.
Data were captured and analysed using the IBM SPSS Statistics software 24. Overall p-values were calculated by Pearson's chi-square or Fisher’s exact test for categorical data and by t-test for metric variables. A p-value < 0.05 was considered as significant. The confidence interval was 95%. The statistical analysis was reviewed by an independent professional statistician.
Between 1991 and 2006, 3907 eligible low-risk full term primiparae were included in the defined cohort group. A total of 1844 women had a water delivery and 2063 women had a bed delivery. The mean age in both groups was 27.9 and 27.4 years, respectively. Birth weights were similar in both groups, averaging 3325g and 3342g, respectively. There were significantly less episiotomies in the water delivery group than in the bed delivery group, 10.5% versus 33.5%.
The duration of delivery with 380 minutes versus 427 minutes, and the duration of the second stage of labor with 48 minutes versus 51 minutes, were significantly shorter in the water delivery group. The use of oxytocin was significantly lower in the waterbirth group, 24% versus 44% in the first stage and 41% versus 75% in the second stage of labor.
The rate of OASIS was 68 (3.7%) in water deliveries versus 125 (6.1%) in bed deliveries. This difference is statistically significant.
Interpretation of results
In this exploratory study the rate of OASIS after water deliveries was lower than after bed deliveries. The following arguments support this result even though it stands in contrast to earlier published data: The “hands on” approach in all water and bed deliveries, the positive effect of warm water, “softening of the perineal tissue” and the less frequent use of oxytocin in the water deliveries.
In our study the so-called “hands on” approach was performed for all women. While earlier data couldn’t show that “hands on” alone decreases OASIS, it is known that in contrast the “hands off” approach is associated with a higher rate of OASIS. To compare water- and bedbirths identical labor management is mandatory, which means the “hands on” approach must be done in water and in bed deliveries. 
Warm water seems to smooth the perineal tissue and make it more elastic. Together with the “hands on” approach this might be a good perineal protection.
The use of oxytocin in the second stage of labor was lower in waterbirths too. This might create more natural contractions with a more homogenous pressure on the perineum, which might also be protective.
The lower rate of episiotomies in water might be another factor that contributes to the lower rate of OASIS.
Concluding message
Water deliveries are popular and for most women more natural. Primiparae have the highest risk of OASIS and damage to the pelvic floor. Water deliveries in a hospital setting, with careful labor management, might be a good idea to prevent OASIS in full term primiparae. The “hands on” approach for all deliveries might be a key issue.
Figure 1 Comparison of demographic factors between water and bed groups
Figure 2 Comparison of perineal injuries between water and bed groups
  1. Cluett ER, Burns E, Cuthbert A. Immersion in water during labour and birth. Cochrane Database Syst Rev. 2018 May 16;5(5):CD000111. doi: 10.1002/14651858.CD000111.pub4. PMID: 29768662; PMCID: PMC6494420
  2. Committee on Obstetric Practice; American Academy of Pediatrics. ACOG Committee Opinion no. 594: Immersion in water during labor and delivery. Obstet Gynecol. 2014 Apr;123(4):912-5. doi: 10.1097/01.AOG.0000445585.52522.14. PMID: 24785637
  3. Preston HL, Alfirevic Z, Fowler GE, Lane S. Does water birth affect the risk of obstetric anal sphincter injury? Development of a prognostic model. Int Urogynecol J. 2019 Jun;30(6):909-915. doi: 10.1007/s00192-019-03879-z. Epub 2019 Feb 19. PMID: 30783705
Funding none Clinical Trial No Subjects Human Ethics Committee Ethical Committee of Kanton Thurgau, Switzerland Helsinki Yes Informed Consent Yes
05/07/2024 10:32:48