Portal de Periódicos da CAPES

Is obstetric anal sphincter injury a risk factor for levator ani muscle avulsion in vaginal delivery?

2015; Wiley; Volume: 49; Issue: 2 Linguagem: Inglês

10.1002/uog.15847

1469-0705

Marta Simó González, Jordi Cassadó Garriga, C. Capel, Oriol Porta Roda, Josep Perelló Capó, Ignasi Gich Saladich,

Pelvic and Acetabular Injuries

Ultrasound in Obstetrics & GynecologyVolume 49, Issue 2 p. 257-262 Original PaperFree Access Is obstetric anal sphincter injury a risk factor for levator ani muscle avulsion in vaginal delivery? M. Simó González, Corresponding Author M. Simó González msimo@santpau.cat Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, SpainCorrespondence to: Dr M. Simó González, Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Mas Casanovas n, i Barcelona 08025, Spain (e-mail: msimo@santpau.cat)Search for more papers by this authorJ. Cassadó Garriga, J. Cassadó Garriga Department of Gynecology and Obstetrics, Hospital Universitari Mútua de Terrassa, Terrassa, SpainSearch for more papers by this authorC. Dosouto Capel, C. Dosouto Capel Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, SpainSearch for more papers by this authorO. Porta Roda, O. Porta Roda Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, SpainSearch for more papers by this authorJ. Perelló Capó, J. Perelló Capó Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, SpainSearch for more papers by this authorI. Gich Saladich, I. Gich Saladich Clinical Epidemiology Unit, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, SpainSearch for more papers by this author M. Simó González, Corresponding Author M. Simó González msimo@santpau.cat Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, SpainCorrespondence to: Dr M. Simó González, Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Mas Casanovas n, i Barcelona 08025, Spain (e-mail: msimo@santpau.cat)Search for more papers by this authorJ. Cassadó Garriga, J. Cassadó Garriga Department of Gynecology and Obstetrics, Hospital Universitari Mútua de Terrassa, Terrassa, SpainSearch for more papers by this authorC. Dosouto Capel, C. Dosouto Capel Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, SpainSearch for more papers by this authorO. Porta Roda, O. Porta Roda Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, SpainSearch for more papers by this authorJ. Perelló Capó, J. Perelló Capó Gynecology and Obstetrics Department, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, SpainSearch for more papers by this authorI. Gich Saladich, I. Gich Saladich Clinical Epidemiology Unit, Hospital Universitari de la Santa Creu i Sant Pau, Universitat Autònoma, Barcelona, SpainSearch for more papers by this author First published: 23 December 2015 https://doi.org/10.1002/uog.15847Citations: 4AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat ABSTRACT Objective To analyze whether women who sustain obstetric anal sphincter injury (OASI) in their first vaginal delivery have a higher incidence of levator ani muscle (LAM) avulsion than do women without OASI. Methods We conducted a prospective observational cohort study of 80 primiparous women who gave birth at our tertiary obstetric unit between September 2011 and July 2013. The women were divided into two groups: women diagnosed with OASI during vaginal delivery (n = 40) and women without OASI (n = 40), matched by mode of delivery and newborn birth weight. Four-dimensional (4D) transperineal ultrasound was performed in all participants at 6–12 months after delivery to assess for integrity or avulsion of the LAM. Ultrasound images were evaluated by two observers who were blinded to group assignment and clinical data. Interobserver agreement was assessed to determine the reproducibility of 4D transperineal ultrasound for diagnosing LAM avulsion. Results We found no statistically significant differences between the two groups. The incidence of LAM avulsion was 24.3% in the OASI group and 34.2% in the control group (P = 0.448). Interobserver agreement in the diagnosis of LAM avulsion in the study population using 4D transperineal ultrasound was 89.5%, with a kappa index of 0.76. Conclusions Our findings do not support OASI as a risk factor for LAM avulsion. Prospective studies in larger populations are needed to establish the biomechanical relationships of the pelvic floor structures involved in vaginal delivery. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd. INTRODUCTION Pelvic floor disorders are seldom life threatening, but they can impact negatively on the health and quality of life of affected women. Evidence linking pelvic floor disorders with vaginal delivery has mounted up in recent years, but the pathophysiological mechanisms involved are not yet fully understood1-3. It is clear, however, that the two main pelvic floor structures involved are the anal sphincter and the levator ani muscle (LAM)4-8. According to Sultan's classification, obstetric anal sphincter injury (OASI) is defined as the presence of Grade III or IV perineal tears that occur during delivery and affect the anal sphincter4. OASI occurs in 2–6% of vaginal deliveries and is the leading cause of postpartum anal incontinence in healthy women. The incidence of mild symptoms of anal incontinence is > 40%, despite primary repair9, 10. The LAM is a striated muscle that plays a crucial role in vaginal delivery, and it has to stretch considerably to allow passage of the baby's head. If the muscle reaches a point of maximal stretch, the muscle fibers, especially those in the puborectalis fascicle, are ruptured and injury occurs11-13. Shek and Dietz defined the tearing, or avulsion, of LAM as a defect or discontinuity of muscle fibers from the lateral pelvic wall near to their insertion13, 14. According to the literature, both magnetic resonance imaging and three- and four-dimensional (3D/4D) ultrasound studies have found that the incidence of LAM avulsion varies between 15% and 36% in first vaginal deliveries12-18. The incidence differs significantly depending on the type of vaginal delivery. In spontaneous deliveries, the incidence of LAM avulsion is 11–13%, while in forceps deliveries it is as high as 62–66%19-22. Symptoms of anal sphincter or LAM tear occurring during delivery often manifest as pelvic floor disorder later in life, when it is difficult to determine the mechanisms involved. Furthermore, OASI and LAM avulsion share common risk factors, such as instrumental vaginal delivery, fetal macrosomia and a prolonged second stage of labor. As some of these factors are interrelated, it is difficult to assess their isolated effects8, 17. The present study was designed to analyze prospectively the relationship between OASI and LAM avulsion by investigating whether women with OASI in their first vaginal delivery had a higher incidence of LAM avulsion than did women without OASI. METHODS This was a prospective, observational cohort study of 80 primiparous women who delivered at our department between 1 September 2011 and 31 July 2013. Our center, a tertiary university hospital with a catchment population of 300 000 inhabitants, delivers about 2000 babies per year. The policy at our center is that spontaneous deliveries are attended by either physicians or midwives, following a common protocol. Instrumental vaginal deliveries are performed only by physicians. OASI is diagnosed by the attending midwife or physician but primary repair is always carried out by a physician, in accordance with established guidelines. The mother can choose the position in which she wants to give birth as long as the perineum is visible to the attendant in order to permit ‘hands-on’ perineal protection. Mediolateral episiotomy is used only when the attendant considers this necessary. This prospective study was approved by the Ethics Committee for Clinical Research at the Hospital de la Santa Creu i Sant Pau. All women who met the inclusion criteria and consented to participate were included in the study, and all gave signed informed consent to participate in it. A research physician other than the principal investigator evaluated the inclusion criteria. The inclusion criteria for the OASI group were primiparous women diagnosed with OASI at the time of their first vaginal delivery, with no previous anal incontinence or antecedents of anal or pelvic floor surgery or any condition that could distort pelvic floor muscle anatomy. Each woman in this group was matched with the next primiparous woman who had the same type of vaginal delivery (spontaneous, vacuum, Thierry spatulas or forceps) and a similar newborn birth weight (± 200 g), but who did not sustain OASI during childbirth (control group). Repair of OASI was undertaken following our specific clinical practice guidelines, based on Sultan's recommendations4. 4D transperineal ultrasound was performed in all participants 6–12 months after delivery to assess the integrity or avulsion of the LAM. At the time of the ultrasound examination, the principal investigator was blinded to group assignment. All ultrasound images were recorded. The ultrasound examination was performed with the woman in the dorsal lithotomy position using a GE Voluson machine (GE Medical Systems, Zipf, Austria) and following the methods standardized by Dietz14. The ultrasound beam was directed cranially to capture an image of the LAM and posteriorly to capture an image of the anal sphincter. The images were obtained at rest and during voluntary contraction of the pelvic floor muscles21-27. To assess the morphology of the LAM, we used the criteria proposed by Dietz24 (Figure 1). Tomographic ultrasound imaging was used to diagnose LAM avulsion, with slices obtained in the axial plane at 2.5-mm intervals, from 5 mm below the plane of minimal hiatal dimensions to 12.5 mm above this plane. LAM avulsion was diagnosed if three central slices (the reference slice and 2.5-mm and 5-mm cranial slices) showed a discontinuity in the fibers of the LAM at the site of its insertion in the os pubis (Figure 2). The 4D transperineal ultrasound was considered positive or negative for each side, and unilateral or bilateral lesions were recorded14. We also captured images of the anal sphincter in all women following the technique and diagnostic criteria for sphincter tear proposed by Shek et al.28. Two observers, the principal investigator and an expert gynecologist with clinical experience in 4D pelvic floor ultrasound, independently evaluated the ultrasound images and applied the same previously agreed criteria for diagnosing LAM avulsion. The learning procedure comprised 20 teaching cases. Both observers were blinded to all clinical data. Figure 1Open in figure viewerPowerPoint Tomographic ultrasound images showing normal appearance of puborectalis component of levator ani muscle. No muscle defect is observed in any of the three central slices. Figure 2Open in figure viewerPowerPoint Tomographic ultrasound images showing right-sided avulsion (arrows) of the puborectalis component of the levator ani muscle in the three central slices. The primary endpoint was to evaluate whether women with OASI had a higher incidence of LAM avulsion, diagnosed using 4D transperineal ultrasound, than did women without OASI29. Our secondary endpoints were to evaluate the efficacy of 4D transperineal ultrasound for the diagnosis of LAM avulsion, based on the percentage of volumes that were adequate for analysis and those that were not evaluable, and to analyze the reproducibility of the technique by means of interobserver agreement using the kappa index. For statistical analysis we used only the data of the expert observer. Statistical analysis The sample size was determined considering previously published data that found an incidence of LAM avulsion of about 30% for all vaginal deliveries (10–40% depending on the type of vaginal delivery)7, 16, 30-32 and that found that OASI was a risk factor for LAM avulsion17, 30. For this calculation, we estimated a difference of 30% in the incidence of LAM avulsion between groups, a 10% rate of missing data, a 5% rate of Type 1 error (alpha = 0.005) and statistical power of 80% (beta = 0.20). Cohen's kappa was used to evaluate interobserver agreement. We used an anonymous database, excluding any information relating to the identification of the women, for data analysis. In the case of categorical variables, bivariate analysis was performed using contingency tables, which were further analyzed using the chi-square or Fisher's exact test. We applied the Mann–Whitney U-test for ordinal variables and the t-test of independent measurements for quantitative variables, with 95% CIs for relevant variables. In all cases the level of significance used was 5% (α = 0.05) with two-tailed analysis. Statistical analysis was performed using the statistical package IBM-SPSS V 21.0 (IBM Corp., Armonk, NY, USA). RESULTS The characteristics of the study population of 80 primiparous women who had a vaginal delivery are summarized in Table 1, with a comparative bivariate analysis of the women according to the presence or absence of OASI. The incidence of OASI in the overall population of women who had a vaginal delivery at our center during the study period was 64/2454 (2.6% (95% CI, 2.01–3.31%)). Of these, 62 (96.9%) had OASI Grade III and two (3.1%) had OASI Grade IV according to Sultan's classification4. Table 1. Characteristics of study population of 80 primiparous women with vaginal delivery and bivariate analysis of those with and those without obstetric anal sphincter injury (OASI) Characteristic Total population (n = 80) OASI (n = 40) No OASI (n = 40) P Age (years) 31.4 ± 5.4 30.9 ± 4.4 31.9 ± 6.3 0.409 Mode of delivery 1 Spontaneous 20 (25.0) 10 (25.0) 10 (25.0) Vacuum 14 (17.5) 7 (17.5) 7 (17.5) Forceps 26 (32.5) 13 (32.5) 13 (32.5) Thierry spatulas 20 (25.0) 10 (25.0) 10 (25.0) Anesthesia 0.026 Epidural 74 (92.5) 34 (85.0) 40 (100.0) Local 6 (7.5) 6 (15.0) — Episiotomy 58 (72.5) 28 (70.0) 30 (75.0) 0.803 Other injury 11 (13.8) 3 (7.5) 8 (20.0) 0.193 Delivery attendant 0.863 Midwife 12 (15.0) 7 (17.5) 5 (12.5) Physician 68 (85.0) 33 (82.5) 35 (87.5) Newborn birth weight (g) 3300 ± 410.5 3295.8 ± 418.2 3304.3 ± 407.9 0.927 Newborn head circumference (mm) 345.8 ± 13.7 344.6 ± 12.7 347.0 ± 14.8 0.443 Puerperium outcome 0.737 Normal 70 (87.5) 34 (85.0) 36 (90.0) Complicated 10 (12.5) 6 (15.0) 4 (10.0) Data are given as mean ± SD or n (%). 4D transperineal ultrasound images for the evaluation of LAM morphology were obtained in 76 (95%) women. Two ultrasound volumes in the OASI group and two in the control group were excluded from analysis, owing to software problems in three and failure to attend appointments in one. Analyzable images were obtained in 75/76 women, therefore we were able to confirm or rule out LAM avulsion in 93.8% of the total group of women and in 98.7% of women for whom images were obtained; the scan was listed as unsuitable for diagnosis in one case. The incidence of LAM avulsion in the total study population was 22/75 women analyzed (29.3% (95% CI, 19.4–41.0%)). The incidence of LAM avulsion as assessed by 4D ultrasound was 9/37 (24.3%) in women with OASI and 13/38 (34.2%) in women without OASI. This difference was not statistically significant (P = 0.448). The incidence of undiagnosed OASI in the control group was 2.5%; a sphincter defect was identified on one 3D transperineal ultrasound image. Agreement on LAM avulsion between observers was 89.5%, with a kappa index of 0.76. The proportion of volumes that were not evaluable for diagnosis was 7.9% for the principal investigator and 1.3% for the expert observer (Table 2). Table 2. Interobserver agreement for diagnosis of levator ani muscle avulsion by four-dimensional transperineal ultrasound in 76 primiparous women after vaginal delivery Observer 1 No avulsion Avulsion Not evaluable Total Observer 2 No avulsion 52 (68.4) — 1 (1.3) 53 (69.7) Avulsion 3 (3.9) 15 (19.7) 4 (5.3) 22 (28.9) Not evaluable — — 1 (1.3) 1 (1.3) Total 55 (72.4) 15 (19.7) 6 (7.9) 76 (100.0) Data are given as n (%). DISCUSSION This study was designed specifically to assess prospectively the relationship between OASI and LAM avulsion in vaginal delivery. The study design was created to control for two important confounding and common risk factors for both complications: birth weight and type of vaginal delivery. We found no significant difference between the incidence of LAM avulsion in women with OASI and those without OASI. These results do not support OASI as a risk factor for LAM avulsion during vaginal delivery. Furthermore, we found a trend towards a lower incidence of LAM avulsion in women with OASI than in those without OASI. These findings contrast with those of previous publications that have suggested that OASI could be a risk factor for LAM avulsion17, 29. One of these studies, however, was retrospective and was conducted in women with pelvic floor dysfunction many years after they had given birth17 and the other was not designed specifically to assess the relationship between OASI and LAM avulsion29. It is therefore difficult to decide whether this link was causal or associative in these studies because the two complications share some risk factors8, 17. We hypothesize several explanations for our unexpected results. One explanation for the non-statistically significant difference in the results could be that our selection criteria – i.e. type of vaginal delivery and birth weight – are strong risk factors for obstetric trauma during childbirth, and gave us a biased population for OASI and LAM avulsion. Our results thus strengthen the importance of these two risk factors for the occurrence of these two complications during vaginal delivery. Another factor for our non-significant results could be the small sample size. We propose an explanation for the unexpected tendency of women who had OASI to have a lower incidence of LAM avulsion. As the LAM is located in a deeper anatomical plane than is the anal sphincter, it is subjected to stretch, elongation and potential injury before the anal sphincter, at the moment when the fetal head passes through the pelvis. Anal-sphincter tear, in contrast, usually occurs as a prolongation of a perineal tear in the superficial plane. As the LAM, therefore, is at risk of lesion earlier than is the anal sphincter, if we want to determine a possible link between these two complications, we should perhaps consider the influence of LAM avulsion on OASI rather than vice-versa. According to our hypothesis, a torn LAM might lead to a slight enlargement of the genital hiatus, reducing the risk of high-degree perineal tearing in the superficial plane and thus reducing the risk of a torn sphincter. On the basis of this notion, we hypothesize that this tendency towards a lower incidence of LAM avulsion among women with OASI might be explained by the LAM's having some kind of protective role over the anal sphincter, but further studies are needed to confirm this hypothesis. Several other findings are worth noting. First, the incidence of OASI (2.6%) in vaginal deliveries in our setting during the study period was within the range reported in the literature (2–6%)4, 9. Second, the overall incidence of LAM within our total study population was 29%, also in the range reported in the literature (20–30%)7, 16. Third, 4D transperineal ultrasound showed a high capacity to obtain and analyze images and had good diagnostic ability for LAM avulsion. We found that the technique was highly reproducible and the learning curve was steep. We consider that the difference between the two investigators regarding the rate of non-evaluable volumes was due to differences in level of experience. The main limitation of this study is that the main inclusion criterion, OASI, was evaluated clinically, so we cannot rule out the possibility of undiagnosed or hidden OASI in women in the control group. The incidence of hidden OASI is 2–5% in vaginal deliveries33-41. Adequate training in knowledge of perineal anatomy and digital examination of the perineum after childbirth comprise the cornerstone for the optimal diagnosis of OASI29. Our department follows a specifically developed program to manage OASI, consisting of a clinical practice guideline and a training plan for all physicians and midwives attending deliveries. Our incidence of OASI is within the range reported in the literature9, 10 and, as we always perform a digital examination of the perineum after vaginal delivery, our incidence of undiagnosed OASI is probably low42. Moreover, during the 4D transperineal ultrasound imaging, we captured images of the anal sphincter in all women included in this study. We found one case with a sphincter defect in the 3D transperineal ultrasound assessment of the 40 women in the control group. This represents a rate of undiagnosed OASI of 2.5%, coinciding with that reported in the literature. In conclusion, OASI was not a risk factor for LAM avulsion during vaginal delivery in our cohort. The biomechanical interaction mechanisms in pelvic floor structures involved in vaginal delivery are complex and not fully known. Further studies in larger populations are needed to investigate the complex biomechanical interactions between pelvic floor structures, especially the anal sphincter and the LAM, and to determine the hypothetical link between OASI and LAM avulsion in vaginal delivery. ACKNOWLEDGMENT We thank Carolyn Newey for her editorial assistance. REFERENCES 1MacLennan AH, Taylor AW, Wilson DH, Wilson D. The prevalence of pelvic floor disorders and their relationship to gender, age, parity and mode of delivery. BJOG 2000; 107: 1460– 1470. 2Memon HU, Handa VL. Pelvic floor disorders following vaginal or caesarean delivery. Curr Opin Obstet Gynecol 2012; 24: 349– 354. 3Cacciatore A, Giordano R, Romano M, La Rosa B, Fonti I. Putative protective effects of cesarean section on pelvic floor disorders. J Neonatal Perinatal Med 2010; 4: 1– 4. 4Sultan AH. Obstetric perineal injury and anal incontinence. Clinical Risk 1999; 5: 193– 196. 5Dietz HP, Simpson JM. Levator trauma is associated with pelvic organ prolapse. BJOG 2008; 115: 979– 984. 6Dietz HP. Clinical consequences of levator trauma. Ultrasound Obstet Gynecol 2012; 39: 367– 371. 7Dietz HP. Pelvic floor trauma in childbirth. Review article. Aust N Z J Obstet Gynaecol 2013; 53: 220– 230. 8Memon HU, Handa VL. Vaginal childbirth and pelvic floor disorders. Womens Health (Lond) 2013; 9: 265– 277; quiz 276–277. 9Nordeval S, Markskog A, Rossaak K, Vonen B. Correlation between anal sphincter defects and anal incontinence following obstetric sphincter tears: assessment using scoring systems for sonographic classification of defects. Ultrasound Obstet Gynecol 2008; 31: 78– 84. 10Sultan AH, Thakar R, Fenner DE. Perineal and Anal Sphincter Trauma Diagnosis and Clinical Management. Springer Science + Business Media: London, UK, 2007; 33– 51. 11Ashton-Miller JA, Delancey JO. On the biomechanics of vaginal birth and common sequelae. Annu Rev Biomed Eng 2009; 11: 163– 176. 12Svabík K, Shek KL, Dietz HP. How much does the levator hiatus have to stretch during childbirth? BJOG 2009; 116: 1657– 1662. 13Shek K, Dietz H. Intrapartum risk factors for levator trauma. BJOG 2010; 117: 1485– 1492. 14Dietz HP. Quantification of major morphological abnormalities of the levator ani. Ultrasound Obstet Gynecol 2007; 29: 329– 334. 15Chan SS, Cheung RY, Yiu AK, Lee LL, Pang AW, Choy KW, Leung TY, Chung TK. Prevalence of levator ani muscle injury in Chinese primiparous women after first delivery. Ultrasound Obstet Gynecol 2012; 39: 704– 709. 16Lien KC, Mooney B, DeLancey JO, Ashton-Miller JA. Levator ani muscle stretch induced by simulated vaginal birth. Obstet Gynecol 2004; 103: 31– 40. 17Lammers K, Prokop M, Vierhout ME, Kluivers KB, Fütterer JJ. A pictorial overview of pubovisceral muscle avulsions on pelvic floor magnetic resonance imaging. Insights Imaging 2013; 4: 431– 441. 18Schwertner-Tiepelmann N, Thakar R, Sultan AH, Tunn R. Obstetric levator ani muscle injuries: current status. Ultrasound Obstet Gynecol 2012; 39: 372– 383. 19Cassadó J, Pessarrodona A, Espuña M, Duran Retamal M, Felgueroso A, Rodriguez Carballeira MJ. Four-dimensional sonographic evaluation of avulsion of the levator ani according to delivery mode. Ultrasound Obstet Gynecol 2011; 38: 701– 706. 20Kearney R, Miller JM, Ashton-Miller JA, DeLancey JO. Obstetric factors associated with levator ani muscle injury after vaginal birth. Obstet Gynecol 2006; 107: 144– 149. 21Dietz HP. Ultrasound imaging of the pelvic floor. Part II: three-dimensional or volume imaging. Ultrasound Obstet Gynecol 2004; 23: 615– 625. 22Dietz HP. Pelvic floor ultrasound: a review. Am J Obstet Gynecol 2010; 202: 321– 334. 23Dietz HP, Shek C. Tomographic ultrasound imaging of the pelvic floor: which levels matter most? Ultrasound Obstet Gynecol 2009; 33: 698– 703. 24Dietz HP, Bernardo MJ, Kirby A, Shek KL. Minimal criteria for the diagnosis of avulsion of the puborectalis muscle by tomographic ultrasound. Int Urogynecol J 2011; 22: 699– 704. 25Santoro GA, Wieczorek AP, Dietz HP, Mellgren A, Sultan H, Shobeiri SA, Stankiewicz A, Bartram C. State of the art: an integrated approach to pelvic floor ultrasonography. Ultrasound Obstet Gynecol 2011; 37: 381– 396. 26Albrich S, Laterza R, Skala C, Salvatore S, Koelbl H, Naumann G. Impact of mode of delivery on levator morphology: a prospective observational study with three dimensional ultrasound early in the postpartum period. BJOG 2012; 119: 51– 61. 27Dietz HP, Kirby A. Modelling the likelihood of levator avulsion in a urogynaecological population. Aust NZ J Obstet Gyn 2010; 50: 268– 274. 28Shek KL, Guzman-Rojas R, Dietz HP. Residual defects of the external anal sphincter following primary repair: an observational study using transperineal ultrasound. Ultrasound Obstet Gynecol 2014; 44: 704– 709. 29Roos AM, Abdool Z, Sultan AH, Thakar R. The diagnostic accuracy of endovaginal and transperineal ultrasound for detecting anal sphincter defects: The PREDICT study. Clin Radiol 2011; 66: 597– 604. 30van Delft K, Thakar R, Sultan AH, Schwertner-Tiepelmann N, Kluivers K. Levator ani muscle avulsion during childbirth: a risk prediction model. BJOG 2014; 121: 1155– 1163; discussion 1163. 31Krofta L, OtÊenáÊek M, KaÊíková E, Feyereisl J. Pubococcygeus–puborectalis trauma after forceps delivery: evaluation of the levator ani muscle with 3D/4D ultrasound. Int Urogynecol J 2009; 20: 1175– 1181. 32Margulies RU, Huebner M, DeLancey JO. Origin and insertion points involved in levator ani muscle defects. Am J Obstet Gynecol 2007; 196: 251.e1– 5. 33Andrews V, Sultan AH, Thakar R, Jones PW. Occult anal sphincter injuries – myth or reality? BJOG 2006; 113: 195– 200. 34Kołodziejczak M, Sudoł-Szopińska I, Stefański R, Panorska AK, Gardyszewska A, Krasnodębski I. Anal endosonographic findings in women after vaginal delivery. Eur J Radiol 2011; 78: 157– 159. 35Kalis V, Chudácek Z, Stepán J Jr, Horák M, Karbanová J, Rokyta Z. Occult anal sphincter tear – up-to-date knowledge. Ceska Gynekol 2007; 72: 234– 240. 36Johnson JK, Lindow SW, Duthie GS. The prevalence of occult obstetric anal sphincter injury following childbirth – literature review. J Matern Fetal Neonatal Med 2007; 20: 547– 554. 37Abdool Z, Sultan AH, Thakar R. Ultrasound imaging of the anal sphincter complex: a review. Br J Radiol 2012; 85: 865– 875. 38Weinstein MM, Pretorius DH, Jung SA, Nager CW, Mittal K. Transperineal three-dimensional ultrasound imaging for detection of anatomical defects in the anal sphincter complex muscles. Clin Gastroenterol Hepatol 2009; 7: 205– 211. 39Lee JH, Pretorius DH, Weinstein M, Guaderrama NM, Nager CW, Mittal RK. Transperineal three-dimensional ultrasound in evaluating anal sphincter muscles. Ultrasound Obstet Gynecol 2007; 30: 201– 209. 40Starck M, Bohe M, Fortling B, Valentin L. Endosonography of the anal sphincter in women of different ages and parity. Ultrasound Obstet Gynecol 2005; 25: 169– 176. 41Valsky DV, Cohen SM, Lipschuetz M, Hochner-Celnikier D, Yagel S. Three-dimensional transperineal ultrasound findings associated with anal incontinence after intrapartum sphincter tears in primiparous women. Ultrasound Obstet Gynecol 2012; 39: 83– 90. 42Simó González M, Porta Roda O, Perelló Capó J, Gich Saladich I, Calaf Alsina J. Mode of vaginal delivery: a modifiable intrapartum risk factor for obstetric anal sphincter injury. Obstet Gynecol Int 2015; 2015: 679470. Citing Literature Volume49, Issue2February 2017Pages 257-262 FiguresReferencesRelatedInformation