Risk of obstetric anal sphincter injury in women having a vaginal birth after a previous caesarean section: A population-based cohort study

Asian-White disparities in obstetric anal sphincter injury: a systematic review and meta-analysis

OBJECTIVE

Obstetrical anal sphincter injury describes a severe injury to the perineum and perianal muscles after birth. Obstetrical anal sphincter injury occurs in approximately 4.4% of vaginal births in the United States; however, racial and ethnic inequities in the incidence of obstetrical anal sphincter injury have been shown in several high-income countries. Specifically, an increased risk of obstetrical anal sphincter injury in individuals who identify as Asian vs those who identify as White has been documented among residents of the United States, Australia, Canada, Western Europe, and the Scandinavian countries. The high rates of obstetrical anal sphincter injury among the Asian diaspora in these countries are higher than obstetrical anal sphincter injury rates reported among Asian populations residing in Asia. A systematic review and meta-analysis of studies in high-income, non-Asian countries was conducted to further evaluate this relationship.

DATA SOURCES

MEDLINE, Ovid, Embase, EmCare, and the Cochrane databases were searched from inception to March 2023 for original research studies.

STUDY ELIGIBILITY CRITERIA

Observational studies using keywords and controlled vocabulary terms related to race, ethnicity and obstetrical anal sphincter injury. All observational studies, including cross-sectional, case-control, and cohort were included. 2 reviewers followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and the Meta-analysis of Observational Studies in Epidemiology recommendations.

METHODS

Meta-analysis was performed using RevMan (version 5.4; Cochrane Collaboration, London, United Kingdom) for dichotomous data using the random effects model and the odds ratios as effect measures with 95% confidence intervals. Subgroup analysis was performed among Asian subgroups. The risk of bias was assessed using the Joanna Briggs Institute Critical Appraisal tools. Meta-regression was used to determine sources of between-study heterogeneity.

Results

A total of 27 studies conducted in 7 countries met the inclusion criteria encompassing 2,337,803 individuals. The pooled incidence of obstetrical anal sphincter injury was higher among Asian individuals than White individuals (pooled odds ratio, 1.64; 95% confidence interval, 1.48-1.80). Subgroup analyses showed that obstetrical anal sphincter injury rates were highest among South Asians and among population-based vs hospital-based studies. Meta-regression showed that moderate heterogeneity remained even after accounting for differences in studies by types of Asian subgroups included, study year, mode of delivery included, and study setting.

Conclusion

Obstetrical anal sphincter injury is more frequent among Asian versus white birthing individuals in multiple high-income, non-Asian countries. Qualitative and quantitative research to elucidate underlying causal mechanisms responsible for this relationship are warranted.

Risk indicators for obstetrical anal sphincter injury in vaginal birth after caesarean section compared to first vaginal delivery

OBJECTIVES

Comparison of the rate of obstetric anal sphincter injury (OASI) between women having their first vaginal birth after caesarean section (CS) and true nulliparous women with a vaginal delivery. Assessment of risk indicators for OASI in women with vaginal birth after one CS (VBAC).

STUDY DESIGN

28 535 women with their first VBAC and a cohort of 275 439 nulliparous women with a vaginal delivery of a liveborn infant in a cephalic position from the Dutch perinatal registry were analyzed. We compared the OASI rate with univariate and multivariate analysis. In women with VBAC possible risk indicators for OASI were assessed using univariate and multivariate logistic regression analysis.

RESULTS

The rate of OASI was 5.2% in women with vaginal birth after CS and 4.0% in women with a first vaginal delivery. The adjusted OR (aOR) for vaginal birth after an elective CS was higher (aOR 1.34, 95% CI 1.23-1.47) compared to vaginal birth after an emergency CS (aOR 1.16, 95% CI 1.08-1.25). In women with vaginal birth after emergency CS, the aOR for the indication non-progressive labor was 1.18 (95% CI 1.08-1.29), whereas CS for suspected fetal distress was not significantly associated with obstetric anal sphincter injury in VBAC. In the 28 535 women with a VBAC, mediolateral episiotomy (MLE), birth weight < 3000 g and maternal age < 25 years were associated with a significantly lower rate of OASI. A gestational age of 42 weeks, birth weight ≥ 3500 g, operative vaginal delivery and duration of the 2nd stage of labour of ≥ 60 min were associated with a significantly higher rate of OASI.

CONCLUSIONS

Women with a VBAC have a higher rate of OASI in comparison with women with a first vaginal delivery, with the exception of women with a vaginal birth after an emergency CS for suspected fetal distress. Factors associated with a significantly lower rate for OASI were MLE, maternal age < 25 and birth weight < 3000 g. A gestational age of 42 weeks, birth weight between 3500 and 4000 g and ≥ 4000 g, operative vaginal delivery and duration of the 2nd stage of delivery longer dan 60 min were associated with a significantly higher rate of OASI.

Diagnosis of maternal birth trauma by pelvic floor ultrasound

BRIEF SUMMARY

Maternal somatic birth trauma due to vaginal delivery is more common than generally assumed and an important cause of future morbidity. Maternal birth trauma may involve both psychological and somatic morbidity, some of it long-term and permanent. Somatic birth trauma is now understood to encompass not just episiotomy, perineal tears and obstetric anal sphincter injuries (OASI), but also trauma to the levator ani muscle, termed 'avulsion'. This review will focus on recent developments in the imaging diagnosis of maternal birth trauma, discuss the most important risk factors and strategies for primary and secondary prevention. Translabial and exo-anal ultrasound allow the assessment of maternal birth trauma in routine clinical practice and enable the use of levator avulsion and anal sphincter trauma as key performance indicators of maternity services. This is likely to lead to a greater awareness of maternal birth trauma amongst maternity caregivers and improved outcomes for patients, not the least due to an increasing emphasis on patient autonomy and informed consent in antenatal and intrapartum care.

Planned mode of birth after previous cesarean section and risk of undergoing pelvic floor surgery: A Scottish population-based record linkage cohort study

BACKGROUND

The global rise in cesarean sections has led to increasing numbers of pregnant women with a history of previous cesarean section. Policy in many high-income settings supports offering these women a choice between planned elective repeat cesarean section (ERCS) or planned vaginal birth after previous cesarean (VBAC), in the absence of contraindications to VBAC. Despite the potential for this choice to affect women's subsequent risk of experiencing pelvic floor disorders, evidence on the associated effects to fully counsel women is lacking. This study investigated the association between planned mode of birth after previous cesarean section and the woman's subsequent risk of undergoing pelvic floor surgery.

METHODS AND FINDINGS

A population-based cohort study of 47,414 singleton term births in Scotland between 1983 to 1996 to women with 1 or more previous cesarean sections was conducted using linked Scottish national routine datasets. Cox regression was used to investigate the association between planned as well as actual mode of birth and women's subsequent risk of having any pelvic floor surgery and specific types of pelvic floor surgery adjusted for sociodemographic, maternal medical, and obstetric-related factors. Over a median of 22.1 years of follow-up, 1,159 (2.44%) of the study population had pelvic floor surgery. The crude incidence rate of any pelvic floor surgery per 1,000 person-years was 1.35, 95% confidence interval (CI) 1.27 to 1.43 in the overall study population, 1.75, 95% CI 1.64 to 1.86 in the planned VBAC group and 0.66, 95% CI 0.57 to 0.75 in the ERCS group. Planned VBAC compared to ERCS was associated with a greater than 2-fold increased risk of the woman undergoing any pelvic floor surgery (adjusted hazard ratio [aHR] 2.38, 95% CI 2.03 to 2.80, p < 0.001) and a 2- to 3-fold increased risk of the woman having surgery for pelvic organ prolapse or urinary incontinence (aHR 3.17, 95% CI 2.47 to 4.09, p < 0.001 and aHR 2.26, 95% CI 1.79 to 2.84, p < 0.001, respectively). Analysis by actual mode of birth showed these increased risks were only apparent in the women who actually had a VBAC, with the women who needed an in-labor non-elective repeat cesarean section having a comparable risk of pelvic floor surgery to those who had an ERCS. The main limitation of this study is the potential for misclassification bias.

CONCLUSIONS

This study suggests that among women with previous cesarean section giving birth to a singleton at term, planned VBAC compared to ERCS is associated with an increased risk of the woman subsequently undergoing pelvic floor surgery including surgery for pelvic organ prolapse and urinary incontinence. However, these risks appear to be only apparent in women who actually give birth vaginally as planned, highlighting the role of vaginal birth rather than labor in pelvic floor dysfunction requiring surgery. The findings provide useful additional information to counsel women with previous cesarean section about the risks and benefits associated with their future birth choices.

Planned mode of birth after previous cesarean section: A structured review of the evidence on the associated outcomes for women and their children in high-income setting

In many high-income settings policy consensus supports giving pregnant women who have had a previous cesarean section a choice between planning an elective repeat cesarean section (ERCS) or planning a vaginal birth after previous cesarean (VBAC), provided they have no contraindications to VBAC. To help women make an informed decision regarding this choice, clinical guidelines advise women should be counseled on the associated risks and benefits. The most recent and comprehensive review of the associated risks and benefits of planned VBAC compared to ERCS in high-income settings was published in 2010 by the US Agency for Healthcare Research and Quality (AHRQ). This paper describes a structured review of the evidence in high-income settings that has been published since the AHRQ review and the literature in high-income settings that has been published since 1980 on outcomes not included in the AHRQ review. Three databases (MEDLINE, EMBASE, and PsycINFO) were searched for relevant studies meeting pre-specified eligible criteria, supplemented by searching of reference lists. Forty-seven studies were identified as meeting the eligibility criteria and included in the structured review. The review suggests that while planned VBAC compared to ERCS is associated with an increased risk of various serious birth-related complications for both the mother and her baby, the absolute risk of these complications is small for either birth approach. The review also found some evidence that planned VBAC compared to ERCS is associated with benefits such as a shorter length of hospital stay and a higher likelihood of breastfeeding. The limited evidence available also suggests that planned mode of birth after previous cesarean section is not associated with the child’s subsequent risk of experiencing adverse neurodevelopmental or health problems in childhood. This information can be used to manage and counsel women with previous cesarean section about their subsequent birth choices. Collectively, the evidence supports existing consensus that there are risks and benefits associated with both planned VBAC and ERCS, and therefore women without contraindications to VBAC should be given an informed choice about planned mode of birth after previous cesarean section. However, further studies into the longer-term effects of planned mode of birth after previous cesarean section are needed along with more research to address the other key limitations and gaps that have been highlighted with the existing evidence.

Increased risk of obstetric anal sphincter injury in women undergoing vaginal delivery after caesarean section: A systematic review and meta-analysis

BACKGROUND

There is increased focus on obstetric anal sphincter injury (OASI) and there are several well-established risk factors such as birthweight, instrumental delivery and median episiotomy. Some studies have found increased risk of OASI in women delivering vaginally after a previous caesarean section (VBAC).

OBJECTIVE

To evaluate whether there is increased prevalence of OASI in VBAC compared with primiparous women.

SEARCH STRATEGY

Literature search using PubMed, Embase and Cochrane databases.

SELECTION CRITERIA

All studies with data on both primiparous women and women undergoing VBAC were included. All included studies were evaluated using the "SIGN - methodology checklist" to verify if the quality was acceptable.

DATA COLLECTION AND ANALYSIS

This systematic review included 23 articles conducted in 11 countries over 19 years. Included studies were analysed using RevMan version 5.4.

MAIN RESULTS

We found increased prevalence of OASI in the VBAC group; 8.18% (95% confidence interval [CI] 8.07-8.29) compared with 6.59% (95% CI 6.56-6.62) in primiparous women. Correspondingly, the meta-analysis revealed increased prevalence for OASI in the VBAC group (odds ratio 1.27, 95% CI 1.10-1.47). We found a high level of heterogeneity (I²  = 98%).

CONCLUSION

Women undergoing VBAC had a higher prevalence of OASI compared with primiparous women.

Risk of obstetric anal sphincter injury among women who birth vaginally after a prior caesarean section: A state-wide cohort study

OBJECTIVE

Vaginal birth after caesarean (VBAC) has been suggested to be associated with an increased risk of obstetric anal sphincter injury (compared with primiparous women who birth vaginally). However, prior studies have been small, or used outdated methodology. We set out to validate whether the risk of obstetric anal sphincter injury among women having their first VBAC is greater than that among primiparous women having a vaginal birth.

DESIGN

State-wide retrospective cohort study.

SETTING

Victoria, Australia.

POPULATION

All births (455,000) between 2009-2014.

METHODS

The risk of severe perineal injury between first vaginal birth and first vaginal birth after previous caesarean section was compared, after adjustment for potential confounding variables. Covariates were examined using logistic regression for categorical data and Wilcoxon rank-sum test for continuous data. Missing data were handled using multiple imputation; the analysis was performed using regression adjustment and Stata v16 multiple imputation and teffects suites.

RESULTS

Women having a VBAC (n=5,429) were significantly more likely than primiparous women (n=123,353) to sustain a 3^rd or 4^th degree tear during vaginal birth (7.1 vs 5.7%, p<0.001). After adjustment for mode of birth, body mass index, maternal age, infant birthweight, episiotomy and epidural, there was a 21% increased risk of severe perineal injury (relative risk 1.21 (95%CI 1.07 - 1.38)).

CONCLUSIONS

Women having their first vaginal birth after caesarean section have a significant increased risk of sustaining a 3^rd or 4^th degree tear, compared with primiparous women having a vaginal birth. Patient counselling and professional guidelines should reflect this increased risk.

Temporal trends in obstetric anal sphincter injury from the first vaginal delivery in Austria, Canada, Norway, and Sweden

INTRODUCTION

Obstetric anal sphincter injuries (OASI) are severe complications that can cause considerable short- and long-term morbidity. Austria, Canada, Norway, and Sweden have similar socio-economic characteristics, and all four countries have access to national birth registers. In this study, we hypothesized that the incidence of OASI should be very similar for different obstetric scenarios in these four countries. Therefore, the aim was to compare the incidence of OASI in these four countries in primiparous women, with spontaneous or instrumental delivery (vacuum or forceps), and in women with a first vaginal birth after cesarean section (VBAC).

MATERIAL AND METHODS

Aggregated data on 1 933 930 vaginally delivered primiparous women and women with VBAC were retrieved from the birth registers gathered in Austria, Canada, Norway, and Sweden. The annual rate of OASI (ICD-10 codes O70.2-O70.3) was presented as the percentage of women with a spontaneous delivery, vacuum or forceps delivery, and a VBAC during the period 2004-2016.

RESULTS

The incidence of OASI varied considerably between countries and over time. Canada and Sweden had the highest rates, and Austria and Norway the lowest. In Norway, the rate of OASI decreased consistently for all types of deliveries after introducing a perineal protection program in 2004 (p < 0.001). During vacuum delivery, the incidence of OASI varied between countries from 4.1% to 15.5% across the study period. In Canada and Norway, the rate of OASI after a forceps delivery was similar in 2004 at ~20% and with differing trajectories to 24.3% (β 0.49) and 6.2% (β -1.15) (trend, all p < 0.001) in 2016.

CONCLUSIONS

This comparative register study suggests that there may be considerable potential for lowering the incidence of OASI. The perineal protection program implemented by Norway has been successful. Each country should critically, without prejudice, analyze their current clinical practices and rate of OASI and consider the best preventive strategy.

Vaginal birth after Cesarean section and levator ani avulsion: a case-control study

OBJECTIVE

The aim of this study was to explore the risk of levator ani muscle (LAM) avulsion and enlargement of the levator hiatus following vaginal birth after Cesarean section (VBAC) in comparison with vaginal delivery in primiparous women.

METHODS

In this two-center observational case-control study, we identified all women who had a term VBAC for their second delivery at the Departments of Obstetrics and Gynecology at the Faculty of Medicine in Pilsen and the 1^st Faculty of Medicine in Prague, Charles University, Czech Republic, between 2012 and 2016. Women with a repeat VBAC, preterm birth or stillbirth were excluded from the study. As a control group, we enrolled a cohort of primiparous women who delivered vaginally during the study period. To increase our control sample, we also invited all primiparous women who delivered vaginally in both participating units between May and June 2019 to participate. All participants were invited for a four-dimensional pelvic floor ultrasound scan to assess LAM trauma. LAM avulsion and the area of the levator hiatus were assessed offline from the stored pelvic floor volumes obtained at rest, during maximum contraction and during Valsalva maneuver. The laterality of the avulsion was also noted. The cohorts were then compared using the χ² test and Wilcoxon's two-sample test according to the normality of the distribution. P < 0.05 was considered statistically significant. Multivariate regression analysis, controlling for age and body mass index (BMI), was also performed.

RESULTS

A total of 356 women had a VBAC for their second delivery during the study period. Of these, 152 (42.7%) attended the ultrasound examination and full data were available for statistical analysis for 141 women. The control group comprised 113 primiparous women. A significant difference was observed between the VBAC group and the control group in age (32.7 vs 30.1 years; P < 0.05), BMI (28.4 vs 27.4 kg/m² ; P < 0.05) and duration of the first and second stages of labor (293.1 vs 345.9 min; P < 0.05 and 27.6 vs 35.3 min; P < 0.05, respectively) at the time of the index birth. The LAM avulsion rate was significantly higher in the VBAC compared with the control group (32.6% vs 18.6%; P = 0.01). The difference between the groups was observed predominantly in the rate of unilateral avulsion and remained significant after controlling for age and BMI (adjusted odds ratio 2.061 (95% CI, 1.103-3.852)). There was no statistically significant difference in the area of the levator hiatus at rest (12.0 vs 12.6 cm² ; P = 0.28) or on maximum Valsalva maneuver (18.6 vs 18.7 cm² ; P = 0.55) between the VBAC and control groups. The incidence of levator hiatal ballooning was comparable between the groups (17.7% and 18.6%; P = 0.86).

CONCLUSIONS

VBAC is associated with a significantly higher rate of LAM avulsion than is vaginal birth in nulliparous women. The difference was significant even after controlling for age and BMI. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Obstetric anal sphincter injury following previous vaginal delivery

INTRODUCTION AND HYPOTHESIS

Obstetric anal sphincter injury (OASI) is a debilitating complication of vaginal delivery. The aim of this study was to identify risk factors for OASI in women with a previous vaginal delivery. We further attempted to detect specific risk factors for severe OASI in this subgroup.

METHODS

We conducted a retrospective cohort study between 2003 and 2019. The study group included women who had a singleton, live, vertex, vaginal delivery at term and who also had at least one previous vaginal delivery. The control group included women with at least one previous vaginal delivery without OASI. General medical history, obstetric history, and ante-, intra- and post-partum data were collected and compared between groups.

RESULTS

Following implementation of the inclusion criteria, 79,176 women were included. Allocation to study groups was according to OASI occurrence: 135 patients (0.2%) had a third- or fourth-degree perineal tear, while 79,041 patients (99.8%) had no such injury. Multivariate analysis revealed that one previous vaginal delivery, birthweight ≥ 3900 g (90th percentile), vacuum-assisted vaginal delivery and episiotomy were associated with increased risk of OASI. Comparison of more severe OASI (3C and 4th-degree) cases to the control group showed similar results with the addition of prolonged second stage and younger age to risk factors associated with severe OASI while episiotomy was no longer significant.

CONCLUSION

In women with a previous vaginal delivery, one vs. two or more previous vaginal deliveries, increased birthweight, vacuum-assisted vaginal delivery and episiotomy are risk factors for OASI.

Antenatal and intrapartum consent: Implications of the NSW Consent Manual 2020

The provision of informed consent for antenatal and intrapartum care remains a contentious issue among healthcare professionals and has been the topic of controversies in the pages of this journal. Recently, the New South Wales (NSW) Department of Health has fundamentally changed the ground rules for the provision of maternity care within the state. In this opinion piece, we try to provide guidance to clinicians to help them deal with the medicolegal environment created by this document which is likely to affect practitioners not just in NSW.

Risk factors for obstetric anal sphincter injury among women undergoing a trial of labor after cesarean

OBJECTIVE

Data regarding the risks of obstetrical anal sphincter injury (OASI) among women who never delivered vaginally undergoing a trial of labor after cesarean (TOLAC) are scarce. We aimed to evaluate the risk factors and the rate of OASI among women undergoing TOLAC who never delivered vaginally.

STUDY DESIGN

A retrospective cohort study of all women undergoing a TOLAC and never delivered vaginally between 3/2011 and 6/2020. Maternal and intrapartum characteristics were compared between OASI and no-OASI groups. We matched groups to earliest gestational age in which OASI has occurred. A further comparison was made between the study cohort and a cohort of primiparous women undergoing a vaginal delivery, including gestational ages at which OASI has occurred in that cohort.

RESULTS

During the study period there were 2061 TOLACs among women without prior vaginal delivery. Of these, 76 % (1566/2061) had a successful vaginal delivery. Overall, 22/2061 (1.1 %) cases of OASI occurred. There was no difference in maternal demographic, obstetrical and medical history characteristics between the study groups. The mean gestational age at TOLAC was lower in the OASI group (39^0/7 ± 1^2/7 vs. 39^5/7 ± 1^2/7, p = 0.012). In multivariable regression analysis, gestational age was negatively associated with OASI [adjusted odds ratio, 95 % (confidence interval) 0.95 (0.91-0.99), for each day increase in gestational age)]. The rate of OASI in the study cohort did not differ from the rate of OASI among primiparous women during the same study period (347/27975, 1.2 %, p = 0.686).

CONCLUSION

Gestational age at delivery is the only predictor of OASI among women with no prior vaginal deliveries undergoing a TOLAC. The incidence of OASI in this population is 1.1 % and does not differ from that of primiparous women.

Risk of anal sphincter injury in trial of labor post cesarean section

INTRODUCTION

We wanted to evaluate whether secundiparas who achieved vaginal birth after cesarean (VBAC) were at an increased risk for obstetric anal sphincter injury (OASI) compared to primiparas who delivered vaginally, with a stratification by the mode of delivery-spontaneous or operative vaginal delivery.

MATERIAL AND METHODS

We conducted a retrospective cohort study of primiparous women who delivered by vacuum-assisted delivery between March 2011 and June 2019. Primiparas delivering vaginally and secundiparas undergoing VBAC were compared. The cohort was further stratified into two categories: spontaneous vaginal delivery and operative vaginal delivery.

RESULTS

Overall, 23 822 primiparas who delivered vaginally and 1596 secundiparas who underwent VBAC were analyzed. Operative vaginal delivery was performed in 4561 deliveries. OASI rate did not differ between the VBAC and primipara groups (1.3% vs 1.8%, P = .142). A total of 20 857 women delivered by spontaneous vaginal delivery, among them 1180 (5.7%) women were secundiparas and 19 677 (94.3%) were primiparas. OASI rate was comparable between the secundiparas undergoing VBAC and primiparas delivering vaginally (17 [1.4%] vs 338 [1.7%], P = .436). A total of 4561 women delivered by operative vaginal delivery, among them 416 (9.1%) were secundiparas and 4145 (90.9%) were primiparas. The rate of operative vaginal deliveries was higher among the VBAC group compared with the primipara group (6.1% vs 17.4%, P < .001). However, women undergoing successful VBAC had lower rates of OASI compared with primiparas (3 [0.7%] vs 96 [2.3%]; odds ratio [OR] 0.30, 95% CI 0.09-0.97, P = .032). After multivariate logistic regression including all statistically significant factors, OASI was not associated with VBAC in spontaneous or operative vaginal deliveries (adjusted OR 0.85, 95% CI 0.51-1.40 and 0.39, 95% CI 0.12-1.28, respectively).

CONCLUSIONS

Secundiparas undergoing VBAC were not at a higher risk of OASI when compared with primiparas delivering vaginally, either in spontaneous or operative vaginal deliveries. This information might aid when counseling women contemplating a trial of labor after cesarean--to address their concerns regarding the risks and benefits of VBAC.

Timing of cesarean and its impact on labor duration and genital tract trauma at the first subsequent vaginal birth: a retrospective cohort study

Background

The objectives of this study were to explore the course of labor and the risk of obstetric anal sphincter injury at the first vaginal birth after cesarean section (fVBAC) in comparison to primiparous vaginal birth (PVB) in women without epidural analgesia and to assess if laboring before the previous cesarean affected these outcomes.

Methods

All fVBACs without epidural analgesia and the subsequent PVBs (controls) between 2012 and 2016 were included in this retrospective cohort study. Data were collected from health records and included maternal demographics, gestational age, and labor details (duration of 1st and 2nd stages, labor induction or augmentation, birthweight, operative vaginal birth, estimated blood loss, extent of childbirth trauma) in both groups as well as cervical dilation at the time of previous cesarean in the fVBAC group. Wilcoxon and Chi-square tests were used for data analyses.

Results

The study comprised 510 women; 255 fVBACs and 255 controls. The majority of fVBACs were after a pre-labor cesarean section – 177 (69.4%). There was a statistically significant difference in the recorded duration of first stage between the fVBACs and controls (289 vs. 347 min respectively, p < .001). Women were less likely to have an intact perineum in the fVBAC group (29.8 vs. 43.1%, p < 0.01), however, there was no statistically significant difference in anal sphincter injury rates between both groups (2.3 vs. 1.9%, p = 0.76). The groups differed in rates of cervical tears requiring suturing (21.2 vs. 12.9%, p = 0.01). On further subgroup analysis, the duration of first stage of labor was shorter in women who previously had a caesarean section late in labor (≥ 8 cm cervical dilatation) compared to a pre-labor cesarean section, however, there were no differences in other outcomes.

Conclusion

Compared to primiparous women having a vaginal birth, women having their first vaginal birth after a cesarean section have a shorter 1st stage of labor (particularly if the cesarean was performed in advanced labor), a higher risk of sustaining cervical lacerations and perineal trauma. However, there was no difference in the risk of sustaining obstetric anal sphincter injuries between the study groups.

Electronic supplementary material

The online version of this article (10.1186/s12884-019-2359-7) contains supplementary material, which is available to authorized users.