Incidence and risk factors for obstetric anal sphincter ruptures, OASIS, following the introduction of preventive interventions. A retrospective cohort study from a Norwegian hospital 2012-2017

Prevention of obstetric anal sphincter injuries with perineal support and lateral episiotomy: A historical cohort study

INTRODUCTION

There are many risk factors for obstetric anal sphincter injury (OASIS) and the interaction between these risk factors is complex and understudied. The many observational studies that have shown a reduction of OASIS rates after implementation of perineal support have short follow-up time. We aimed to study the effect of integration of active perineal support and lateral episiotomy on OASIS rates over a 15-year period and to study interactions between risk factors known before delivery.

MATERIAL AND METHODS

We performed a historical cohort study over the periods 1999-2006 and 2007-2021 at Stavanger University Hospital, Norway. The main outcome was OASIS rates. Women without a previous cesarean section and a live singleton fetus in cephalic presentation at term were eligible. The department implemented in 2007 the Finnish concept of active perineal protection, which includes support of perineum, control of fetal expulsion, good communication with the mother and observation of perineal stretching. The practice of mediolateral episiotomy was replaced with lateral episiotomy when indicated. We analyzed the OASIS rates in groups with and without episiotomy stratified for delivery mode, fetal position at delivery and for parity, and adjusted for possible confounders (maternal age, gestational age, oxytocin augmentation and epidural analgesia).

RESULTS

We observed a long-lasting reduction in OASIS rates from 4.9% to 1.9% and an increase in episiotomy rates from 14.4% to 21.8%. Lateral episiotomy was associated with lower OASIS rates in nulliparous women with instrumental vaginal deliveries and occiput anterior (OA) position; 3.4% vs 10.1% (OR 0.31; 95% CI: 0.24-0.40) and 6.1 vs 13.9% (OR 0.40; 95% CI: 0.19-0.82) in women with occiput posterior (OP) position. Lateral episiotomy was also associated with lower OASIS rates in nulliparous women with spontaneous deliveries and OA position; 2.1% vs 3.2% (OR 0.62; 95% CI: 0.49-0.80). The possible confounders had little confounding effects on the risk of OASIS in groups with and without episiotomy.

CONCLUSIONS

We observed a long-lasting reduction in OASIS rates after implementation of preventive procedures. Lateral episiotomy was associated with lower OASIS rates in nulliparous women with an instrumental delivery. Special attention should be paid to deliveries with persistent OP position.

Neonatal head circumference as a risk factor for obstetric anal sphincter injuries: a systematic review and meta-analysis

OBJECTIVE

Between 53% and 79% of women will sustain some degree of perineal laceration during vaginal delivery. Third- and fourth-degree perineal lacerations are known as obstetric anal sphincter injuries. Timely diagnosis and prompt treatment of obstetric anal sphincter injuries can help to prevent the development of severe consequences like fecal incontinence, urinary incontinence, and rectovaginal fistula. Neonatal head circumference is routinely measured postpartum but is often not mentioned as a risk factor for obstetric anal sphincter injuries in clinical guidelines. Thus far, no review article on the risk factors for obstetric anal sphincter injuries has discussed the role of neonatal head circumference. This study aimed to review and analyze the relationship between head circumference and the occurrence of obstetric anal sphincter injuries among previous studies to conclude whether head circumference should be recognized as an important risk factor.

DATA SOURCES

Through study screening on Google Scholar, PubMed, Scopus, and Science Direct for articles published between 2013 to 2023, followed by assessment of eligibility, this study ended up reviewing 25 studies, 17 of which were included in the meta-analysis.

STUDY ELIGIBILITY CRITERIA

Only studies that reported both the neonatal head circumference and the occurrence of obstetric anal sphincter injuries were included in this review.

METHODS

The included studies were appraised using the Dartmouth Library risk of bias assessment checklist. Qualitative synthesis was based on the study population, findings, adjusted confounding factors, and suggested causative links in each study. Quantitative synthesis was conducted using calculation and pooling of odds ratios and inverse variance using Review Manager 5.4.1.

RESULTS

A statistically significant association between head circumference and obstetric anal sphincter injuries was reported in 21 of 25 studies; 4 studies reported that head circumference was a true independent risk factor. A meta-analysis of the studies that reported neonatal head circumference as a dichotomous categorical variable with a cutoff point of 35±1 cm yielded statistically significant pooled results (odds ratio, 1.92; 95% confidence interval, 1.80-2.04).

CONCLUSION

The risk for obstetric anal sphincter injuries increased as the neonatal head circumference increased-this should be considered in decision-making during labor and postpartum management to attain the best outcome.

Which elements were significant in reducing obstetric anal sphincter injury? A prospective follow-up study

Background

To examine which elements of an obstetric anal sphincter injury (OASI) care bundle were protective for OASI. Several interventional trials showed that application of a care bundle involving a hands-on approach to perineal protection may reduce the risk of OASI. Previously, we found that only the element “hand on the fetal head” in itself was protective, although the risk of a type 2 error was calculated to be 50%.

Methods

A prospective follow-up study in an obstetric department in Denmark with 3200 deliveries per year. We included a cohort of 10,383 women giving birth vaginally from gestational week 22 + 0 from 2016 through 2019. We documented on a person-level the five elements of the care bundle together with maternal and obstetrical characteristics. The elements were 1) communication, 2) visible perineum, 3) hand on fetal head, 4) perineal support and 5) certification. Regression analysis was used for analysis of associations. The primary outcome measure was OASI.

Results

The total rate of OASI in vaginally delivering women was 1.9%. The incidence was 3.2% in nulliparous women giving birth vaginally. The rate of cesarean section was 16.5% and for episiotomy 2.4%. The reduction in the incidence of OASI was sustained since 2013. Hand on the fetal head and perineal support both were protective factors for OASI. In case of a nulliparous woman with a neonate weighing 3500 g giving birth spontaneously, the relative risk (RR) for OASI was 0.50 (95% CI 0.49- 0.51) with use of hand on the fetal head together with perineal support against no use. Similarly, with a nulliparous woman giving birth to a neonate of 3500 g by vacuum extraction, the RR for OASI was 0.65 (95% CI 0.62-0.68) against no use.

Conclusions

Both hand on the fetal head and perineal support were associated with a reduced risk of OASI.

Risk of obstetric anal sphincter injury with fundal pressure in second stage of labor: Transperineal ultrasound study

AIMS

Clinical management of the second stage of labor and effectiveness of preventive measures for severe perineal tears are controversial. The aim of this study was to evaluate the effect of using uterine fundal pressure during the second stage of delivery on obstetric anal sphincter injury (OASI), among primiparous women using three-dimensional (3D) transperineal ultrasonography.

METHODS

A total of 73 women who had their first vaginal birth were included in the study, the fundal pressure group included women where the fundal pressure maneuver was applied (n = 37); and the control group included women who delivered spontaneously without fundal pressure (n = 36). Tomographic ultrasound imaging with 3D transperineal assessment was performed within 48 h of delivery, internal anal sphincter (IAS) and external anal sphincter (EAS) defect were determined.

RESULTS

Five (13.5%) women in the fundal pressure group, seven (20%) women in the control group had complete EAS defect (p = 0.4). Complete IAS defect was observed in one (2.7%) woman in the fundal pressure group and two (5.7%) women in the control group (p = 0.5). A Half-moon sign was observed in one woman in both groups (p = 0.9). The rate of other signs was similar in both groups. Multivariate regression models revealed that none of age, fetal birth weight, episiotomy, length of the second stage of labor, fundal pressure application status, and number were independent predictors of complete IAS or EAS defect.

CONCLUSION

Fundal pressure with mediolateral episiotomy during the second stage of delivery does not increase the rate of OASI detected with ultrasonography.

The role of fetal head circumference in the formation of obstetric anal sphincter injuries following vacuum deliveries among primiparous women

PURPOSE

To evaluate the association of sonographic fetal head circumference (HC) with obstetric anal sphincter injury (OASIS) occurrence among primiparous women who underwent vacuum-assisted delivery (VAD).

METHODS

A retrospective study of all primiparous women who delivered at term by VAD between 2011 and 2019 and underwent ultrasound with fetal biometry within 1 week prior to delivery. Women who suffered OASIS were compared to women without OASIS.

RESULTS

Overall, 74 of 3222 (2.3%) primiparous women suffered an OASIS. As compared with control, women with OASIS were younger (median 28 vs. 30 years, p = 0.001), had higher BMI (median 28.2 vs. 26.9 kg/m², p = 0.03), and had a longer second stage of labor (median 190 vs. 168 min, p = 0.01). Fetal head circumference was larger in the OASIS group (mean 334 vs. 330 mm, p = 0.03), occiput posterior fetal head position was more prevalent (12 (16%) vs. 232 (7.4%), OR [95% CI]: 2.43 (1.29-4.57), p = 0.004), and the rate of mediolateral episiotomy performed was lower (58 (78.0%) vs. 2777 (88.2%), OR [95% CI]: 0.48 (0.27-0.85), p = 0.01). Multivariate regression modeling identified higher fetal HC (aOR [95% CI] 1.03 (1.001-1.06), p = 0.04) and occiput posterior (aOR [95% CI] 2.5 (1.16-5.71), p = 0.01) as independently positively associated with OASIS. Mediolateral episiotomy and maternal age were independently negatively associated with an OASIS (aOR [95% CI] 0.39 (0.18-0.85), p = 0.01); aOR [95% CI] 0.4 (0.17-0.60), p = 0.001).

CONCLUSIONS

Sonographic large fetal HC is associated with OASIS occurrence during VAD. The only modifiable predictor of OASIS detected was mediolateral episiotomy, found to be protective against OASIS.

Parturition mode recommendation and symptoms of pelvic floor disorders after obstetric anal sphincter injuries

INTRODUCTION AND HYPOTHESIS

Our primary objective was to evaluate parturition mode (PM) recommendations following obstetric anal sphincter injuries (OASIs) and adherence to these recommendations and to evaluate recurrence of OASIs in women who had a subsequent vaginal delivery (VD). The hypothesis was that adherence to the PM recommendations leads to a reasonable OASI recurrence rate.

METHODS

This was a retrospective observational cohort study of patients with previous OASIs between 2010 and 2016. After an outpatient visit including 3D transperineal ultrasound to screen for pelvic floor and anal sphincter injuries, all patients received recommendations for a subsequent PM. Patients were invited to complete validated questionnaires 2 to 5 years post-OASIs.

RESULTS

The majority of invited patients (265/320) attended follow-up, with 264 receiving a recommendation for PM. Only 5.6% did not adhere to the received recommendation. One hundred sixty-one patients delivered again, 58% had a VD, and 42% had a cesarean section (CS). Recurrence of OASIs was observed in 4.3% of the patients that had a VD. Fecal incontinence occurred in 4.9%, however any form of anal incontinence in 48% of patients. While dyspareunia was common in patients with residual external anal sphincter (EAS) injuries and levator ani muscle (LAM) avulsions, anal pain occurred more frequently in EAS injuries and fecal incontinence in LAM avulsions.

CONCLUSIONS

This study showed that the vast majority of patients followed PM recommendations, and this resulted in a low recurrence of OASIs with a high CS rate. Fecal incontinence after OASIs was correlated with the degree of OASIs.