The Journal of Maternal-Fetal & Neonatal Medicine
ISSN: 1476-7058 (Print) 1476-4954 (Online) Journal homepage: http://www.tandfonline.com/loi/ijmf20
Is the risk of obstetric anal sphincter injuries increased in vaginal twin deliveries? Hadar Rosen, Nir Melamed, Rania Okby, Ori Nevo & Jon Barrett To cite this article: Hadar Rosen, Nir Melamed, Rania Okby, Ori Nevo & Jon Barrett (2015): Is the risk of obstetric anal sphincter injuries increased in vaginal twin deliveries?, The Journal of Maternal-Fetal & Neonatal Medicine, DOI: 10.3109/14767058.2015.1059813 To link to this article: http://dx.doi.org/10.3109/14767058.2015.1059813
Accepted author version posted online: 02 Jul 2015. Published online: 28 Jul 2015. Submit your article to this journal
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Date: 05 November 2015, At: 22:55
http://informahealthcare.com/jmf ISSN: 1476-7058 (print), 1476-4954 (electronic) J Matern Fetal Neonatal Med, Early Online: 1–4 ! 2015 Informa UK Ltd. DOI: 10.3109/14767058.2015.1059813
ORIGINAL ARTICLE
Is the risk of obstetric anal sphincter injuries increased in vaginal twin deliveries? Hadar Rosen, Nir Melamed, Rania Okby, Ori Nevo, and Jon Barrett
Downloaded by [Central Michigan University] at 22:55 05 November 2015
Division of Feto Maternal Medicine, Department of Obstetrics and Gynecology, Sunnybrook Health Science Centre, University of Toronto, Toronto, Ontario, Canada Abstract
Keywords
Objective: Vaginal twin deliveries have a higher rate of intrapartum interventions. We aimed to determine whether these characteristics are associated with an increased rate of obstetric anal sphincter injuries compared with singleton. Study design: Retrospective study of all twin pregnancies undergoing vaginal delivery trial was conducted from January 2000–September 2014. Sphincter injury rate compared with all concurrent singleton vaginal deliveries. Multivariable analysis was used to determine twin delivery association with sphincter injuries while adjusting for confounders. Results: About 717 eligible twin deliveries. Outcome was compared with 33 886 singleton deliveries. Twin pregnancies characterized by a higher rate of nulliparity (54.8% versus 49.5%, p ¼ 0.005), labor induction (42.7% versus 29.1%, p50.001), and instrumental deliveries (27.5% versus 16.7%, p50.001), lower gestational (34.6 ± 3.3 versus 38.8 ± 2.3, p50.001), and lower birth weight. Total breech extraction was performed in 29.0% (208/717) of twin deliveries. Overall obstetric sphincter injury rate was significantly lower in the twins group (2.8% versus 4.4%, p ¼ 0.03, OR ¼ 0.6, 95% CI 0.4–0.9), due to lower rate of 3rd degree tears in twins versus singletons (2.2% versus 4.0%, p ¼ 0.02), rate of 4th degree tears similar among the groups (0.6% versus 0.4%, p ¼ 0.5). In multivariable analysis, sphincter injuries were associated with nulliparity (OR ¼ 3.9, 95% CI 3.4–4.5), forceps (OR ¼ 6.8, 95% CI 5.8–7.8), vacuum (OR ¼ 2.9, 95% CI 2.5–3.3), earlier gestational age (OR ¼ 0.2, 95% CI 0.1–0.3), episiotomy (OR ¼ 0.8, 95% CI 0.7–0.9), and birth weight over 3500 g (OR ¼ 1.8, 95% CI 1.6–2.0). However, the association between twins (versus singletons) deliveries and sphincter injuries was lost after adjustment for delivery gestational age (OR ¼ 0.7, 95% CI 0.4–1.2). Conclusion: Despite a higher rate of intrapartum interventions, the rate of sphincter injuries is lower in twins versus singleton deliveries, mainly due to a lower gestational age at delivery.
Anal sphincter injuries, instrumental delivery, OASIS, twin delivery
Introduction Obstetric anal sphincter injuries (OASIS) refer to third and fourth degree perineal tears [1]. There is a considerable variation in the incidence of OASIS. The reported rate of anal sphincter injury range from 0.1% to 8.0% [2–10] and is higher for forceps deliveries and vacuum extractions than for spontaneous deliveries. There is evidence of increasing incidence of OASIS in the past few decades [11], yet it remains uncertain whether this reflects a genuine increase or merely greater awareness and more accurate diagnosis. OASIS are associated with significant short- and long-term maternal physical and emotional morbidities such as bowel symptoms, sexual dysfunction, pain, and embarrassment [2–5,7–10]. Vaginal twin delivery represents an important
History Received 3 May 2015 Revised 2 June 2015 Accepted 4 June 2015 Published online 28 July 2015
challenge in obstetrics as it often involves intrapartum interventions, including instrumental delivery and total breech extraction [12,13]. In addition, in many cases, these interventions are performed in an urgent manner, most commonly due to fetal distress of the second twin [12,14]. Since some of these interventions, such as instrumental delivery, have been previously shown to be associated with OASIS [15–19], it is possible that these unique features of twins delivery may predispose women to an increased risk of OASIS. Interestingly, information on the incidence of OASIS in twins is limited [20]. Thus, the aim of the current study was to test the hypothesis that OASIS are more common in vaginal twins compared with singletons deliveries.
Methods Address for correspondence: Hadar Rosen, Division of Feto Maternal Medicine, Department of Obstetrics and Gynecology, Sunnybrook Health Science Centre, University of Toronto, Hadar Rosen, 2075 Bayview Avenue, Toronto, ON, Canada M4N 3M5. Tel: +1 416 480 4920. E-mail: [email protected]
Study population This was a retrospective cohort study of all women who underwent a trial of vaginal delivery in a single tertiary
2
H. Rosen et al.
referral center between January 2000 and September 2014. The rate of OASIS in women with twin pregnancies (twins group) was compared with that in women with a singleton pregnancy (singletons group). Women who underwent a planned caesarean section (CS) or those who underwent an intrapartum CS prior to the delivery of twin A, high-order multiple gestations, pregnancy complicated by major fetal anomalies and women delivering prior to 24 weeks were excluded from both groups. The study protocol was approved by the local Research Ethics Board.
Downloaded by [Central Michigan University] at 22:55 05 November 2015
Data collection Data were obtained from the comprehensive perinatal database of the Sunnybrook Health Sciences Centre (SHSC), a tertiary medical center. The multiples Clinic in SHSC, established in 1996, serves as a regional referral center for twin pregnancies. The following information was extracted: demographic information, medical and obstetrical history, pregnancy related complications, labor and delivery complications, and information on perineal injury. Definitions A third-degree tear was defined as a perineal injury involving the external or internal anal sphincter muscles but not the rectal mucosa. A fourth-degree tear was defined as a perineal injury involving the rectal mucosa [21]. The diagnosis of OASIS in our center is routinely confirmed and repaired by an attending obstetrician. Episiotomies are performed only when indicated and are medio-lateral. Guidelines for induction of labor used in our clinic are as follows: Unless otherwise medically indicated, for diamniotic–dichorionic twin pregnancies, labor is induced at a gestational age of 37 + 5–38 + 6 weeks. For monoamniotic– dichorionic twin pregnancies, labor is induced at a gestational age of 37 + 0 weeks. Data analysis Data analysis was performed with the SPSS v21.0 software (SPSS Inc., Chicago, IL). Students’ t-test and the 2 test were used to compare continuous and categorical variables between the groups, respectively. Multivariable logistic regression analysis was performed to determine whether twin gestation is independently associated with OASIS while adjusting for potential confounders. Differences were considered significant when p value was less than 0.05.
Results Demographic and obstetrical characteristics Overall 34 603 women were eligible for the study, of them 717 (2.1%) had twins and 33 886 (97.9%) had a singleton pregnancy. The demographic and obstetric characteristics of the women in the twins and singletons groups are presented in Table 1. Women in the twins group were more likely to be nulliparous and deliver at an earlier gestational age, and had a higher rate of gestational diabetes and hypertensive complications (Table 1). Maternal age and rate of prior cesarean section were similar for the two groups (Table 1).
J Matern Fetal Neonatal Med, Early Online: 1–4
Table 1. Demographic and obstetric characteristics of the twins and singletons groups.
Characteristic Maternal age (years) 435 years Nulliparity Previous CS GA at delivery (weeks) 537 + 0 534 + 0 532 + 0 Male fetal sex Twin A Twin B GDM Hypertensive complications
Twins, N ¼ 717
Singletons, N ¼ 33 886
32.5 ± 5.1 199 (27.8) 393 (54.8) 9 (1.3) 34.6 ± 3.3 436 (60.8) 220 (30.7) 145 (20.2)
32.4 ± 5.0 8901 (26.3) 16 763 (49.5) 757 (2.2) 38.8 ± 2.3 2606 (7.7) 1120 (3.3) 921 (2.7) 17 170 (50.7)
361 367 34 69
(50.3) (51.2) (4.7) (9.6)
839 (2.5) 1416 (4.2)
p value 0.4 0.4 0.005 0.08 50.001 50.001 50.001 50.001 0.9 0.9 50.001 50.001
Data are presented as N (%) or mean ± SD. CS, cesarean section; GA, gestational age; GDM, gestational diabetes. Bold value indicates p50.05.
Table 2. Delivery outcome in the twins and singleton groups.
Outcome Labor induction Epidural Forceps delivery Any twin Twin A Twin B Vacuum delivery Any twin Twin A Twin B Any instrumental delivery Any twin Twin A Twin B Breech extraction of twin B CS for twin B Birth weight (g) Twin A Twin B Combined weight Episiotomy
Twins, N ¼ 717
Singletons, N ¼ 33 886
306 (42.7) 634 (88.4)
9864 (29.1) 24 920 (73.6) 2141 (6.3)
p value 50.001 50.001 50.001 0.6 0.7
79 (11.0) 49 (6.8) 48 (6.7) 3621 (10.7)
50.001 0.08 0.002
136 (19.0) 62 (8.6) 103 (14.4) 5653 (16.7) 197 109 146 208 1
(27.5) (15.2) (20.4) (29.0) (0.1)
2261 ± 624 2240 ± 604 4501 ± 1187 107 (14.9)
N/A N/A 3329 ± 589
50.001 0.3 0.009 N/A N/A 50.001 50.001
4683 (13.8)
0.4
Data are presented as N (%) or mean ± SD. CS, cesarean section. Bold value indicates p50.05.
Labor and delivery characteristics Women in the twins group were characterized by a higher rate of labor induction and use of epidural analgesia (Table 2). The rate of forceps delivery for each of the twins was similar to that observed in the singletons group (6.8% and 6.7% versus 6.3%), although the overall rate of forceps in the twins group (for any of the twins) was significantly higher than in singletons (11.0% versus 6.3%, p50.001) (Table 2). The rate of vacuum delivery for twin A was similar to that in singletons, but the rate of vacuum for twin B as well as the overall rates of vacuum delivery were significantly higher among twins (Table 2). The birth weight of either twin was lower than the mean birth weight in the singletons group. The rate of episiotomy was similar for the two groups (Table 2). The rate of
OASIS in twin vaginal deliveries
DOI: 10.3109/14767058.2015.1059813
Table 3. Rate of obstetric laceration in the twins and singleton groups.
Outcome
Twins, Singletons, N ¼ 717 N ¼ 33 886 p value OR (95% CI)
OASIS 20 (2.8) 1501 (4.4) 3rd degree perineal tear 16 (2.2) 1366 (4.0) 4th degree perineal tear 4 (0.6) 138 (0.4)
0.03 0.02 0.5
0.6 (0.4–0.97) 0.5 (0.3–0.9) 1.4 (0.5–3.7)
Data are presented as N (%). OASIS, obstetric anal sphincter injury; OR, odds ratio; CI, confidence interval. Bold value indicates p50.05.
Table 4. Factors associated with increased risk of OASIS – multivariable analysis.
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Variable Twins versus singletons Age 435 years Nulliparity GA 534 weeks Forceps Vacuum Birth weight 43500 g Episiotomy
3rd degree 0.6 0.9 4.2 0.2 5.8 2.7 1.7 0.8
4th degree
(0.4–1.1) 1.6 (0.5–4.9) (0.8–1.1) 0.7 (0.5–1.1) (3.6–4.9) 1.9 (1.2–3.0) (0.1–0.3) 0.3 (0.1–2.0) (5.0–6.8) 12.9 (8.5–19.4) (2.3–3.1) 4.3 (2.9–6.3) (1.5–1.9) 2.4 (1.7–3.4) (0.7–0.97) 0.6 (0.4–0.9)
Any 0.7 0.9 3.9 0.2 6.8 2.9 1.8 0.8
(0.4–1.2) (0.8–1.1) (3.4–4.5) (0.1–0.3) (5.8–7.8) (2.5–3.3) (1.6–2.0) (0.7–0.9)
Data are presented as odds ratio (95%-confidence interval) and reflect the results of multivariable logistic regression analysis. GA, gestational age. Bold value indicates p50.05.
non-cephalic presentation and need for total breech extraction with or without internal podalic version in the twins group was 29.0% (Table 2). Rate of obstetric lacerations in the twins and singleton groups – univariate analysis Twins delivery was associated with a lower rate of OASIS (2.8% versus 4.4%, p ¼ 0.03, OR ¼ 0.6, 95% CI 0.4–0.97), mainly due to a lower rate of third-degree tears (2.2% versus 4.0%, p ¼ 0.02, OR ¼ 0.5, 95% CI 0.3–0.9) (Table 3). The rate of fourth-degree tears was lower and similar in the two groups (0.6% versus 0.4%, p ¼ 0.5). Association between twin delivery and OASIS – multivariable analysis In order to determine whether the association of twins delivery with OASIS is independent, we used multivariable logistic regression analysis to control for potential confounders (Table 4). The following factors were associated with an increased risk for OASIS: nulliparity, instrumental delivery, and birth weight 43500 g. In contrast, gestational age of less than 34 weeks and the use of episiotomy were associated with a decreased risk for OASIS (Table 4). However, following the introduction of gestational age at delivery into the model, the association between twins delivery (versus singletons) and OASIS was lost (OR ¼ 0.7, 95% CI 0.4–1.2).
Discussion The aim of the current study was to determine whether the unique characteristics of vaginal twin deliveries increase the risk for OASIS compared with singleton deliveries. Our main finding is that the rate of OASIS in twins is lower than in
3
singletons despite a higher rate of instrumental deliveries in twins, and this is mainly attributed to the lower gestational age at delivery in twin pregnancies. OASIS is an important complication that may result in significant physical and emotional sequelae [22]. Therefore, identifying patients that are at higher risk for OASIS may facilitate primary prevention as well as the detection and appropriate management of OASIS. While there is abundant data regarding OASIS in singleton deliveries [15–19], most of these studies excluded twin gestations and, therefore, data available with respect to OASIS in twins is limited [20]. The decision to exclude twin pregnancies from most previous studies can be justified by the fact that the characteristics of twin deliveries differ from those of singleton deliveries. For instance, twin deliveries involve a higher rate of interventions such as instrumental deliveries [12–14], a well-established risk factor for OASIS [18]. However, the worldwide increase in the incidence of twin pregnancies [23] and the recent evidence regarding the safety of vaginal twin delivery [24] are expected to result in an increase in the number of vaginal twin deliveries, emphasizing the need for data directly addressing complications of vaginal deliveries in twins. We were able to identify only a single study addressing OASIS in twin deliveries [20]. Porat et al. reported 20 cases of OASIS in twin pregnancies. In agreement with our findings, the rate of OASIS among twins was lower than in singletons (1.3% versus 2.6%). Instrumental deliveries are known to be a major risk factor for of OASIS [18,25]. Thus, given that twin deliveries may be associated with a higher rate of instrumental deliveries and other intrapartum interventions [12–14], we hypothesized that the incidence of OASIS will be higher in twin compared with singleton deliveries. Indeed, we found the rate of instrumental deliveries to be higher in the twins group. Yet, contrary to our expectation, this was not accompanied by a similar increase in the rate of OASIS which was actually lower in the twins group. Using multivariate analysis, we were able to determine that this was mainly attributed to the lower gestational age at delivery and thus the lower birth weight in that group. Another possible factor contributing to the lower rate of OASIS in twins may be that due to the nature of vaginal twin deliveries, the likelihood that a skilled and experienced obstetrician will be present at the time of delivery is greater in the cases of twins versus singletons deliveries. Our study is not without limitations. Although it encompasses many years of practice in a tertiary twin referral center, the number of OASIS cases in the current cohort is relatively small. In addition, due to the retrospective nature of the current study, information on certain factors such as the position of the fetal head, which has been previously shown to affect the risk of OASIS, was not available. Yet this study holds the strength of presenting important data regarding the incidence of OASIS in twin pregnancies while controlling for potential confounders. In summary, our data indicate that the incidence of OASIS in twin vaginal deliveries is lower compared with singleton deliveries despite the higher rate of instrumental interventions, mainly due to lower gestational age at delivery in twins. In the management of every twin pregnancy, the pride of place discussion refers to the planned mode of delivery.
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The findings of the current study suggest that clinicians can reassure patients that although interventions may be more common in vaginal twin deliveries, the overall risk of OASIS is at most not increased. More research is needed to identify risk factors for OASIS that are specific to the twin pregnancies population.
Declaration of interest The authors report that they have no conflicts of interest.
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References 1. Sultan AH, Thakar R. Third and fourth degree tears. In: Sultan AH, Thakar R, Fenner DE, eds. Perineal and anal sphincter trauma. London: Springer; 2007:33–51. 2. Sangalli MR, Floris L, Faltin D, Weil A. Anal incontinence in women with third or fourth degree perineal tears and subsequent vaginal deliveries. Aust NZ J Obstet Gynaecol 2000;40:244–8. 3. Lewicky CE, Valentin C, Saclarides TJ. Sexual function following sphincteroplasty for women with third-and fourth-degree perineal tears. Dis Colon Rectum 2004;47:1650–4. 4. Sze EH. Anal incontinence among women with one versus two complete third-degree perineal lacerations. Int J Gynaecol Obstet: Off Organ Int Feder Gynaecol Obst 2005;90:213–17. 5. Andrews V, Thakar R, Sultan AH. Outcome of obstetric anal sphincter injuries (OASIS)-role of structured management. Int Urogynecol J Pelvic Floor Dysfunct 2009;20:973–8. 6. Andrews V, Thakar R, Sultan AH. Structured hands-on training in repair of obstetric anal sphincter injuries (OASIS): an audit of clinical practice. Int Urogynecol J Pelvic Floor Dysfunct 2009;20: 193–9. 7. Roos AM, Thakar R, Sultan AH. Outcome of primary repair of obstetric anal sphincter injuries (OASIS): does the grade of tear matter? Ultrasound Obstet Gynecol: Off J Int Soc Ultrasound Obst Gynecol 2010;36:368–74. 8. Huebner M, Gramlich NK, Rothmund R, et al. Fecal incontinence after obstetric anal sphincter injuries. Int J Gynaecol Obstet 2013; 121:74–7. 9. Ramalingam K, Monga AK. Outcomes and follow-up after obstetric anal sphincter injuries. Int Urogynecol J 2013;24:1495–500. 10. Reid AJ, Beggs AD, Sultan AH, et al. Outcome of repair of obstetric anal sphincter injuries after three years. Int J Gynaecol Obstet: Off Organ Int Feder Gynaecol Obst 2014;127:47–50.
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11. Laine K, Gissler M, Pirhonen J. Changing incidence of anal sphincter tears in four Nordic countries through the last decades. Eur J Obstet, Gynecol, Reprod Biol 2009;146:71–5. 12. Barrett JF. Twin delivery: method, timing and conduct. Best Pract Res Clin Obstet Gynaecol 2014;28:327–38. 13. Yang Q, Wen SW, Chen Y, et al. Occurrence and clinical predictors of operative delivery for the vertex second twin after normal vaginal delivery of the first twin. Am J Obstet Gynecol 2005;192: 178–84. 14. Robinson C, Chauhan SP. Intrapartum management of twins. Clin Obstet Gynecol 2004;47:248–62. 15. Groutz A, Hasson J, Wengier A, et al. Third-and fourth-degree perineal tears: prevalence and risk factors in the third millennium. Am J Obstet Gynecol 2011;204:347.e1–4. 16. Ampt AJ, Ford JB, Roberts CL, Morris JM. Trends in obstetric anal sphincter injuries and associated risk factors for vaginal singleton term births in New South Wales 2001–2009. Aust NZ J Obstet Gynaecol 2013;53:9–16. 17. Gurol-Urganci I, Cromwell DA, Edozien LC, et al. Third-and fourth-degree perineal tears among primiparous women in England between 2000 and 2012: time trends and risk factors. Int J Obstet Gynaecol 2013;120:1516–25. 18. Melamed N, Gavish O, Eisner M, et al. Third-and fourth-degree perineal tears – incidence and risk factors. J Matern–Fetal Neonatal Med 2013;26:660–4. 19. Burrell M, Dilgir S, Patton V, et al. Risk factors for obstetric anal sphincter injuries and postpartum anal and urinary incontinence: a case–control trial. Int Urogynecol J 2015;26:383–9. 20. Porat S, Baud D, Farine D. Obstetric anal sphincter injuries in vaginal delivery of twins: associated risk factors and comparison with singletons. Int Urogynecol J 2013;24:769–74. 21. Royal College of Obstetricians and Gynaecologists. The Management of Third-and Fourth-Degree Perineal Tears. Greentop Guideline No. 29. March, 2007. 22. Baud D, Meyer S, Vial Y, et al. Pelvic floor dysfunction 6 years post-anal sphincter tear at the time of vaginal delivery. Int Urogynecol J 2011;22:1127–34. 23. Fell DB, Joseph K. Temporal trends in the frequency of twins and higher-order multiple births in Canada and the United States. BMC Pregnancy Childbirth 2012;12:103. 24. Barrett JF, Hannah ME, Hutton EK, et al. A randomized trial of planned cesarean or vaginal delivery for twin pregnancy. N Engl J Med 2013;369:1295–305. 25. Mazouni C, Porcu G, Bretelle F, et al. Risk factors for forceps delivery in nulliparous patients. Acta Obstet Gynecol Scand 2006; 85:298–301.
ISSN: 1476-7058 (Print) 1476-4954 (Online) Journal homepage: http://www.tandfonline.com/loi/ijmf20
Is the risk of obstetric anal sphincter injuries increased in vaginal twin deliveries? Hadar Rosen, Nir Melamed, Rania Okby, Ori Nevo & Jon Barrett To cite this article: Hadar Rosen, Nir Melamed, Rania Okby, Ori Nevo & Jon Barrett (2015): Is the risk of obstetric anal sphincter injuries increased in vaginal twin deliveries?, The Journal of Maternal-Fetal & Neonatal Medicine, DOI: 10.3109/14767058.2015.1059813 To link to this article: http://dx.doi.org/10.3109/14767058.2015.1059813
Accepted author version posted online: 02 Jul 2015. Published online: 28 Jul 2015. Submit your article to this journal
Article views: 24
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ijmf20 Download by: [Central Michigan University]
Date: 05 November 2015, At: 22:55
http://informahealthcare.com/jmf ISSN: 1476-7058 (print), 1476-4954 (electronic) J Matern Fetal Neonatal Med, Early Online: 1–4 ! 2015 Informa UK Ltd. DOI: 10.3109/14767058.2015.1059813
ORIGINAL ARTICLE
Is the risk of obstetric anal sphincter injuries increased in vaginal twin deliveries? Hadar Rosen, Nir Melamed, Rania Okby, Ori Nevo, and Jon Barrett
Downloaded by [Central Michigan University] at 22:55 05 November 2015
Division of Feto Maternal Medicine, Department of Obstetrics and Gynecology, Sunnybrook Health Science Centre, University of Toronto, Toronto, Ontario, Canada Abstract
Keywords
Objective: Vaginal twin deliveries have a higher rate of intrapartum interventions. We aimed to determine whether these characteristics are associated with an increased rate of obstetric anal sphincter injuries compared with singleton. Study design: Retrospective study of all twin pregnancies undergoing vaginal delivery trial was conducted from January 2000–September 2014. Sphincter injury rate compared with all concurrent singleton vaginal deliveries. Multivariable analysis was used to determine twin delivery association with sphincter injuries while adjusting for confounders. Results: About 717 eligible twin deliveries. Outcome was compared with 33 886 singleton deliveries. Twin pregnancies characterized by a higher rate of nulliparity (54.8% versus 49.5%, p ¼ 0.005), labor induction (42.7% versus 29.1%, p50.001), and instrumental deliveries (27.5% versus 16.7%, p50.001), lower gestational (34.6 ± 3.3 versus 38.8 ± 2.3, p50.001), and lower birth weight. Total breech extraction was performed in 29.0% (208/717) of twin deliveries. Overall obstetric sphincter injury rate was significantly lower in the twins group (2.8% versus 4.4%, p ¼ 0.03, OR ¼ 0.6, 95% CI 0.4–0.9), due to lower rate of 3rd degree tears in twins versus singletons (2.2% versus 4.0%, p ¼ 0.02), rate of 4th degree tears similar among the groups (0.6% versus 0.4%, p ¼ 0.5). In multivariable analysis, sphincter injuries were associated with nulliparity (OR ¼ 3.9, 95% CI 3.4–4.5), forceps (OR ¼ 6.8, 95% CI 5.8–7.8), vacuum (OR ¼ 2.9, 95% CI 2.5–3.3), earlier gestational age (OR ¼ 0.2, 95% CI 0.1–0.3), episiotomy (OR ¼ 0.8, 95% CI 0.7–0.9), and birth weight over 3500 g (OR ¼ 1.8, 95% CI 1.6–2.0). However, the association between twins (versus singletons) deliveries and sphincter injuries was lost after adjustment for delivery gestational age (OR ¼ 0.7, 95% CI 0.4–1.2). Conclusion: Despite a higher rate of intrapartum interventions, the rate of sphincter injuries is lower in twins versus singleton deliveries, mainly due to a lower gestational age at delivery.
Anal sphincter injuries, instrumental delivery, OASIS, twin delivery
Introduction Obstetric anal sphincter injuries (OASIS) refer to third and fourth degree perineal tears [1]. There is a considerable variation in the incidence of OASIS. The reported rate of anal sphincter injury range from 0.1% to 8.0% [2–10] and is higher for forceps deliveries and vacuum extractions than for spontaneous deliveries. There is evidence of increasing incidence of OASIS in the past few decades [11], yet it remains uncertain whether this reflects a genuine increase or merely greater awareness and more accurate diagnosis. OASIS are associated with significant short- and long-term maternal physical and emotional morbidities such as bowel symptoms, sexual dysfunction, pain, and embarrassment [2–5,7–10]. Vaginal twin delivery represents an important
History Received 3 May 2015 Revised 2 June 2015 Accepted 4 June 2015 Published online 28 July 2015
challenge in obstetrics as it often involves intrapartum interventions, including instrumental delivery and total breech extraction [12,13]. In addition, in many cases, these interventions are performed in an urgent manner, most commonly due to fetal distress of the second twin [12,14]. Since some of these interventions, such as instrumental delivery, have been previously shown to be associated with OASIS [15–19], it is possible that these unique features of twins delivery may predispose women to an increased risk of OASIS. Interestingly, information on the incidence of OASIS in twins is limited [20]. Thus, the aim of the current study was to test the hypothesis that OASIS are more common in vaginal twins compared with singletons deliveries.
Methods Address for correspondence: Hadar Rosen, Division of Feto Maternal Medicine, Department of Obstetrics and Gynecology, Sunnybrook Health Science Centre, University of Toronto, Hadar Rosen, 2075 Bayview Avenue, Toronto, ON, Canada M4N 3M5. Tel: +1 416 480 4920. E-mail: [email protected]
Study population This was a retrospective cohort study of all women who underwent a trial of vaginal delivery in a single tertiary
2
H. Rosen et al.
referral center between January 2000 and September 2014. The rate of OASIS in women with twin pregnancies (twins group) was compared with that in women with a singleton pregnancy (singletons group). Women who underwent a planned caesarean section (CS) or those who underwent an intrapartum CS prior to the delivery of twin A, high-order multiple gestations, pregnancy complicated by major fetal anomalies and women delivering prior to 24 weeks were excluded from both groups. The study protocol was approved by the local Research Ethics Board.
Downloaded by [Central Michigan University] at 22:55 05 November 2015
Data collection Data were obtained from the comprehensive perinatal database of the Sunnybrook Health Sciences Centre (SHSC), a tertiary medical center. The multiples Clinic in SHSC, established in 1996, serves as a regional referral center for twin pregnancies. The following information was extracted: demographic information, medical and obstetrical history, pregnancy related complications, labor and delivery complications, and information on perineal injury. Definitions A third-degree tear was defined as a perineal injury involving the external or internal anal sphincter muscles but not the rectal mucosa. A fourth-degree tear was defined as a perineal injury involving the rectal mucosa [21]. The diagnosis of OASIS in our center is routinely confirmed and repaired by an attending obstetrician. Episiotomies are performed only when indicated and are medio-lateral. Guidelines for induction of labor used in our clinic are as follows: Unless otherwise medically indicated, for diamniotic–dichorionic twin pregnancies, labor is induced at a gestational age of 37 + 5–38 + 6 weeks. For monoamniotic– dichorionic twin pregnancies, labor is induced at a gestational age of 37 + 0 weeks. Data analysis Data analysis was performed with the SPSS v21.0 software (SPSS Inc., Chicago, IL). Students’ t-test and the 2 test were used to compare continuous and categorical variables between the groups, respectively. Multivariable logistic regression analysis was performed to determine whether twin gestation is independently associated with OASIS while adjusting for potential confounders. Differences were considered significant when p value was less than 0.05.
Results Demographic and obstetrical characteristics Overall 34 603 women were eligible for the study, of them 717 (2.1%) had twins and 33 886 (97.9%) had a singleton pregnancy. The demographic and obstetric characteristics of the women in the twins and singletons groups are presented in Table 1. Women in the twins group were more likely to be nulliparous and deliver at an earlier gestational age, and had a higher rate of gestational diabetes and hypertensive complications (Table 1). Maternal age and rate of prior cesarean section were similar for the two groups (Table 1).
J Matern Fetal Neonatal Med, Early Online: 1–4
Table 1. Demographic and obstetric characteristics of the twins and singletons groups.
Characteristic Maternal age (years) 435 years Nulliparity Previous CS GA at delivery (weeks) 537 + 0 534 + 0 532 + 0 Male fetal sex Twin A Twin B GDM Hypertensive complications
Twins, N ¼ 717
Singletons, N ¼ 33 886
32.5 ± 5.1 199 (27.8) 393 (54.8) 9 (1.3) 34.6 ± 3.3 436 (60.8) 220 (30.7) 145 (20.2)
32.4 ± 5.0 8901 (26.3) 16 763 (49.5) 757 (2.2) 38.8 ± 2.3 2606 (7.7) 1120 (3.3) 921 (2.7) 17 170 (50.7)
361 367 34 69
(50.3) (51.2) (4.7) (9.6)
839 (2.5) 1416 (4.2)
p value 0.4 0.4 0.005 0.08 50.001 50.001 50.001 50.001 0.9 0.9 50.001 50.001
Data are presented as N (%) or mean ± SD. CS, cesarean section; GA, gestational age; GDM, gestational diabetes. Bold value indicates p50.05.
Table 2. Delivery outcome in the twins and singleton groups.
Outcome Labor induction Epidural Forceps delivery Any twin Twin A Twin B Vacuum delivery Any twin Twin A Twin B Any instrumental delivery Any twin Twin A Twin B Breech extraction of twin B CS for twin B Birth weight (g) Twin A Twin B Combined weight Episiotomy
Twins, N ¼ 717
Singletons, N ¼ 33 886
306 (42.7) 634 (88.4)
9864 (29.1) 24 920 (73.6) 2141 (6.3)
p value 50.001 50.001 50.001 0.6 0.7
79 (11.0) 49 (6.8) 48 (6.7) 3621 (10.7)
50.001 0.08 0.002
136 (19.0) 62 (8.6) 103 (14.4) 5653 (16.7) 197 109 146 208 1
(27.5) (15.2) (20.4) (29.0) (0.1)
2261 ± 624 2240 ± 604 4501 ± 1187 107 (14.9)
N/A N/A 3329 ± 589
50.001 0.3 0.009 N/A N/A 50.001 50.001
4683 (13.8)
0.4
Data are presented as N (%) or mean ± SD. CS, cesarean section. Bold value indicates p50.05.
Labor and delivery characteristics Women in the twins group were characterized by a higher rate of labor induction and use of epidural analgesia (Table 2). The rate of forceps delivery for each of the twins was similar to that observed in the singletons group (6.8% and 6.7% versus 6.3%), although the overall rate of forceps in the twins group (for any of the twins) was significantly higher than in singletons (11.0% versus 6.3%, p50.001) (Table 2). The rate of vacuum delivery for twin A was similar to that in singletons, but the rate of vacuum for twin B as well as the overall rates of vacuum delivery were significantly higher among twins (Table 2). The birth weight of either twin was lower than the mean birth weight in the singletons group. The rate of episiotomy was similar for the two groups (Table 2). The rate of
OASIS in twin vaginal deliveries
DOI: 10.3109/14767058.2015.1059813
Table 3. Rate of obstetric laceration in the twins and singleton groups.
Outcome
Twins, Singletons, N ¼ 717 N ¼ 33 886 p value OR (95% CI)
OASIS 20 (2.8) 1501 (4.4) 3rd degree perineal tear 16 (2.2) 1366 (4.0) 4th degree perineal tear 4 (0.6) 138 (0.4)
0.03 0.02 0.5
0.6 (0.4–0.97) 0.5 (0.3–0.9) 1.4 (0.5–3.7)
Data are presented as N (%). OASIS, obstetric anal sphincter injury; OR, odds ratio; CI, confidence interval. Bold value indicates p50.05.
Table 4. Factors associated with increased risk of OASIS – multivariable analysis.
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Variable Twins versus singletons Age 435 years Nulliparity GA 534 weeks Forceps Vacuum Birth weight 43500 g Episiotomy
3rd degree 0.6 0.9 4.2 0.2 5.8 2.7 1.7 0.8
4th degree
(0.4–1.1) 1.6 (0.5–4.9) (0.8–1.1) 0.7 (0.5–1.1) (3.6–4.9) 1.9 (1.2–3.0) (0.1–0.3) 0.3 (0.1–2.0) (5.0–6.8) 12.9 (8.5–19.4) (2.3–3.1) 4.3 (2.9–6.3) (1.5–1.9) 2.4 (1.7–3.4) (0.7–0.97) 0.6 (0.4–0.9)
Any 0.7 0.9 3.9 0.2 6.8 2.9 1.8 0.8
(0.4–1.2) (0.8–1.1) (3.4–4.5) (0.1–0.3) (5.8–7.8) (2.5–3.3) (1.6–2.0) (0.7–0.9)
Data are presented as odds ratio (95%-confidence interval) and reflect the results of multivariable logistic regression analysis. GA, gestational age. Bold value indicates p50.05.
non-cephalic presentation and need for total breech extraction with or without internal podalic version in the twins group was 29.0% (Table 2). Rate of obstetric lacerations in the twins and singleton groups – univariate analysis Twins delivery was associated with a lower rate of OASIS (2.8% versus 4.4%, p ¼ 0.03, OR ¼ 0.6, 95% CI 0.4–0.97), mainly due to a lower rate of third-degree tears (2.2% versus 4.0%, p ¼ 0.02, OR ¼ 0.5, 95% CI 0.3–0.9) (Table 3). The rate of fourth-degree tears was lower and similar in the two groups (0.6% versus 0.4%, p ¼ 0.5). Association between twin delivery and OASIS – multivariable analysis In order to determine whether the association of twins delivery with OASIS is independent, we used multivariable logistic regression analysis to control for potential confounders (Table 4). The following factors were associated with an increased risk for OASIS: nulliparity, instrumental delivery, and birth weight 43500 g. In contrast, gestational age of less than 34 weeks and the use of episiotomy were associated with a decreased risk for OASIS (Table 4). However, following the introduction of gestational age at delivery into the model, the association between twins delivery (versus singletons) and OASIS was lost (OR ¼ 0.7, 95% CI 0.4–1.2).
Discussion The aim of the current study was to determine whether the unique characteristics of vaginal twin deliveries increase the risk for OASIS compared with singleton deliveries. Our main finding is that the rate of OASIS in twins is lower than in
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singletons despite a higher rate of instrumental deliveries in twins, and this is mainly attributed to the lower gestational age at delivery in twin pregnancies. OASIS is an important complication that may result in significant physical and emotional sequelae [22]. Therefore, identifying patients that are at higher risk for OASIS may facilitate primary prevention as well as the detection and appropriate management of OASIS. While there is abundant data regarding OASIS in singleton deliveries [15–19], most of these studies excluded twin gestations and, therefore, data available with respect to OASIS in twins is limited [20]. The decision to exclude twin pregnancies from most previous studies can be justified by the fact that the characteristics of twin deliveries differ from those of singleton deliveries. For instance, twin deliveries involve a higher rate of interventions such as instrumental deliveries [12–14], a well-established risk factor for OASIS [18]. However, the worldwide increase in the incidence of twin pregnancies [23] and the recent evidence regarding the safety of vaginal twin delivery [24] are expected to result in an increase in the number of vaginal twin deliveries, emphasizing the need for data directly addressing complications of vaginal deliveries in twins. We were able to identify only a single study addressing OASIS in twin deliveries [20]. Porat et al. reported 20 cases of OASIS in twin pregnancies. In agreement with our findings, the rate of OASIS among twins was lower than in singletons (1.3% versus 2.6%). Instrumental deliveries are known to be a major risk factor for of OASIS [18,25]. Thus, given that twin deliveries may be associated with a higher rate of instrumental deliveries and other intrapartum interventions [12–14], we hypothesized that the incidence of OASIS will be higher in twin compared with singleton deliveries. Indeed, we found the rate of instrumental deliveries to be higher in the twins group. Yet, contrary to our expectation, this was not accompanied by a similar increase in the rate of OASIS which was actually lower in the twins group. Using multivariate analysis, we were able to determine that this was mainly attributed to the lower gestational age at delivery and thus the lower birth weight in that group. Another possible factor contributing to the lower rate of OASIS in twins may be that due to the nature of vaginal twin deliveries, the likelihood that a skilled and experienced obstetrician will be present at the time of delivery is greater in the cases of twins versus singletons deliveries. Our study is not without limitations. Although it encompasses many years of practice in a tertiary twin referral center, the number of OASIS cases in the current cohort is relatively small. In addition, due to the retrospective nature of the current study, information on certain factors such as the position of the fetal head, which has been previously shown to affect the risk of OASIS, was not available. Yet this study holds the strength of presenting important data regarding the incidence of OASIS in twin pregnancies while controlling for potential confounders. In summary, our data indicate that the incidence of OASIS in twin vaginal deliveries is lower compared with singleton deliveries despite the higher rate of instrumental interventions, mainly due to lower gestational age at delivery in twins. In the management of every twin pregnancy, the pride of place discussion refers to the planned mode of delivery.
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H. Rosen et al.
The findings of the current study suggest that clinicians can reassure patients that although interventions may be more common in vaginal twin deliveries, the overall risk of OASIS is at most not increased. More research is needed to identify risk factors for OASIS that are specific to the twin pregnancies population.
Declaration of interest The authors report that they have no conflicts of interest.
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