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Morbidity and Mortality Associated With Forceps and Vacuum Delivery at Outlet, Low, and Midpelvic Station

Open AccessPublished:October 23, 2018DOI:https://doi.org/10.1016/j.jogc.2018.06.018

      Abstract

      Objective

      This study sought to quantify perinatal and maternal morbidity and mortality associated with forceps and vacuum delivery compared with Caesarean delivery in the second stage of labour and to estimate whether these associations differed by pelvic station.

      Methods

      The investigators conducted a population-based, retrospective cohort study of term singleton deliveries by operative delivery with prolonged second stage of labour in Canada (2003-2013) using national hospitalization data. The primary study outcomes were severe perinatal morbidity and mortality (i.e., seizures, assisted ventilation, severe birth trauma, and perinatal death) and severe maternal morbidity and mortality (i.e., severe postpartum hemorrhage, cardiac complication, and maternal death). Logistic regression was used to estimate adjusted odds ratios (aOR) and 95% confidence intervals (CI) after stratifying by indication (dystocia or fetal distress). The Breslow-Day chi-square test for heterogeneity in ORs was used to test effect modification by pelvic station (outlet, low, or midpelvic).

      Results

      There were 61 106 deliveries included in the study. Among women with dystocia, forceps and vacuum deliveries were associated with higher rates of perinatal morbidity and mortality compared with Caesarean delivery (forceps: aOR 1.56; 95% CI 1.13–2.17; vacuum: aOR 1.44; 95% CI 1.06–1.97). Vacuum delivery was associated with lower rates of maternal morbidity and mortality compared with Caesarean delivery (dystocia: aOR 0.64; 95% CI 0.51–0.81; fetal distress: aOR 0.43; 95% CI 0.32–0.57). Pelvic station did not significantly modify the associations between forceps or vacuum and perinatal or maternal morbidity and mortality.

      Conclusion

      Forceps and vacuum delivery is associated with increased rates of severe perinatal morbidity and mortality compared with Caesarean delivery among women with dystocia, whereas vacuum delivery is associated with decreased rates of severe maternal morbidity and mortality.

      Résumé

      Objectif

      Cette étude visait à quantifier la mortalité et la morbidité périnatales et maternelles associées à l'accouchement par forceps et par ventouse en comparaison avec la césarienne, durant le deuxième stade du travail, et à évaluer si les résultats diffèrent selon la station pelvienne.

      Méthodologie

      Les chercheurs ont mené une étude de cohorte rétrospective en population générale portant sur les accouchements opératoires de grossesses monofœtales à terme au Canada où le deuxième stade du travail s’était prolongé. Ils se sont servis pour ce faire des données nationales sur les hospitalisations (2003-2013). Les issues primaires à l’étude étaient la morbidité et la mortalité périnatales graves (c.-à-d. convulsions, ventilation assistée, traumatisme de la naissance grave et décès périnatal), et la morbidité et la mortalité maternelles graves (c.-à-d. hémorragie postpartum grave, complication cardiaque et décès maternel). Une régression logistique a été utilisée pour estimer les rapports de cotes ajustés (RCA) et les IC à 95 %, après une stratification selon l'indication (dystocie ou détresse fœtale). Le test de Breslow-Day, un test du chi carré permettant de juger de l'hétérogénéité des RC, a été utilisé pour examiner la modification de l'effet selon la station pelvienne (vulve, détroit inférieur ou détroit moyen).

      Résultats

      Au total, 61 106 accouchements ont été pris en compte dans cette étude. Dans les cas de dystocie, les accouchements par forceps et par ventouse étaient associés à des taux plus élevés de morbidité et de mortalité périnatales comparativement aux césariennes (forceps – RCA : 1,56; IC à 95 % : 1,13-2,17; ventouse – RCA : 1,44; IC à 95 % : 1,06-1,97). L'accouchement par ventouse était associé à des taux plus faibles de morbidité et de mortalité maternelles comparativement à la césarienne (dystocie – RCA : 0,64; IC 95 % : 0,51-0,81; détresse fœtale – RCA : 0,43; IC à 95 % : 0,32-0,57). La prise en compte de la station pelvienne n'a pas entraîné de modification significative des associations entre les accouchements par forceps ou par ventouse et la morbidité et la mortalité périnatales ou maternelles.

      Conclusion

      Les accouchements par forceps et par ventouse sont associés à des taux plus élevés de morbidité et de mortalité périnatales graves par rapport aux césariennes chez les femmes présentant une dystocie, alors que l'accouchement par ventouse est associé à des taux plus faibles de morbidité et de mortalité maternelles graves.

      Key Words

      INTRODUCTION

      There is currently insufficient evidence regarding the perinatal and maternal safety of operative vaginal versus Caesarean delivery given fetal distress or dystocia in the second stage of labour. This has resulted in wide variations in the use of operative vaginal delivery worldwide.
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      10.7% in Canada in 2012,
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      Temporal and regional variations in operative vaginal delivery in Canada by pelvic station, 2004-2012.
      and 16.4% in Ireland in 2010.
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      Wide differences in mode of delivery within Europe: risk‐stratified analyses of aggregated routine data from the Euro‐Peristat study.
      Although many industrialized settings have tended to favour Caesarean delivery in recent decades,
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      Temporal and regional variations in operative vaginal delivery in Canada by pelvic station, 2004-2012.
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      ,
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      increasing the rate of operative vaginal delivery is currently advocated as a strategy to curb the rising frequency of Caesarean delivery, especially in the United States.
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      The extant literature on perinatal and maternal morbidity following operative vaginal delivery compared with Caesarean delivery is inconsistent,
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      Early maternal and neonatal morbidity associated with operative delivery in second stage of labour: a cohort study.
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      Evaluation of delivery options for second-stage events.
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      at least partly because most previous studies were limited by the absence of information on pelvic station, a key determinant of perinatal and maternal outcomes.
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      • et al.
      Operative vaginal delivery.
      • Hagadorn-Freathy AS
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      Validation of the 1988 ACOG forceps classification system.
      Our previous work comparing midpelvic operative vaginal deliveries with Caesarean delivery found increased rates of perinatal and maternal morbidity and mortality following midpelvic forceps and vacuum delivery, particularly birth and obstetric trauma.
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      Perinatal and maternal morbidity and mortality after attempted operative vaginal delivery at midpelvic station.
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      Perinatal and maternal morbidity and mortality among term singletons following midcavity operative vaginal delivery versus caesarean delivery.
      However, it is not clear whether these associations would differ at outlet or low pelvic station. We therefore carried out a study with two objectives: first, to estimate rates of severe perinatal and maternal morbidity and mortality following operative vaginal delivery at outlet, low, and midpelvic station compared with Caesarean delivery; and second, to determine whether these associations differed by pelvic station.

      MATERIALS AND METHODS

      Data were obtained from the Canadian Institute for Health Information's Discharge Abstract Database. The study population included all term (37–41 weeks gestation) singletons delivered in Canada (excluding Quebec) by operative vaginal or Caesarean delivery between April 2003 and March 2013. The database included linked maternal and newborn information on demographic characteristics, labour and delivery, and diagnoses and interventions. Trained health records personnel abstracted information into the database from medical charts by using standardized definitions, and data consistency and accuracy were ensured through routine quality assurance checks. Diagnoses and procedures in the database represent notes in the medical chart made by physicians and were coded using the ICD-10-CA and the Canadian Classification for Interventions. The accuracy of the perinatal information in the database has been demonstrated in validation studies.
      • Joseph KS
      • Fahey J
      Validation of perinatal data in the Discharge Abstract Database of the Canadian Institute for Health Information.
      All operative vaginal deliveries are carried out in the second stage of labour, whereas Caesarean deliveries can be carried out in either the first or second stage. Data source constraints precluded restricting Caesarean deliveries to those that occurred in the second stage of labour. We therefore restricted all operative vaginal and Caesarean deliveries to those with a prolonged second stage of labour identified by diagnosis code (ICD-10-CA O631) to ensure an appropriate comparison.
      Deliveries were excluded if the infant had any congenital anomaly or if the mother had a hypertensive disorder, diabetes mellitus, or a placental abnormality. Deliveries were stratified by indication for operative delivery (dystocia or fetal distress).
      • Henry OA
      • Gregory KD
      • Hobel CJ
      • et al.
      Using ICD-9 codes to identify indications for primary and repeat cesarean sections: agreement with clinical records.
      Forceps deliveries were grouped into outlet, low, and midpelvic deliveries on the basis of the Classification According to Station and Rotation (-5 to +5 cm).
      • Cunningham FG
      • Leveno KJ
      • Bloom SL
      • et al.
      Operative vaginal delivery.
      Delivery by vacuum extraction was grouped into outlet, low, midpelvic, and not otherwise specified categories on the basis of the same classification system.
      • Cunningham FG
      • Leveno KJ
      • Bloom SL
      • et al.
      Operative vaginal delivery.
      The study included two primary outcomes: composite severe perinatal morbidity and mortality and composite severe maternal morbidity and mortality. Composite severe perinatal morbidity and mortality included neonatal seizures, assisted ventilation by endotracheal tube, severe birth trauma (intracranial laceration and hemorrhage, skull fracture, severe injury to the central or peripheral nervous systems, long bone injury, subaponeurotic hemorrhage, and injury to the liver or spleen), stillbirth, and neonatal death. Composite severe maternal morbidity and mortality included severe postpartum hemorrhage (postpartum hemorrhage requiring transfusion), shock, sepsis, cardiac complications, acute renal failure, obstetric embolism, evacuation of incisional hematoma, and death. Secondary outcomes included all birth trauma (intracranial hemorrhage and laceration; injury to the central or peripheral nervous systems, scalp, or skeleton; and other birth injury), severe birth trauma, obstetric trauma (third- and fourth-degree perineal tears; cervical and high vaginal lacerations; injury to pelvic organs, joints, and ligaments; hematoma of the pelvis; extension of uterine incision; and other obstetric trauma) and severe perineal lacerations (third- and fourth-degree). The inclusion and exclusion criteria, indications for operative delivery, confounders, and outcomes of interest, along with the associated ICD-10-CA and Canadian Classification of Health Interventions codes used in the study, are listed in Table A.1 in the Appendix.
      Adjusted odds ratios (aOR) and 95% confidence intervals (CIs) were estimated using multivariable logistic regression to express the relationship between forceps and vacuum delivery (at outlet, low, midpelvic, and all stations combined) and the composite outcomes, with Caesarean delivery as the reference group. The models were adjusted for maternal age, parity, birth weight, province of residence, and fiscal year. Modification of the effect of mode of delivery on the study outcomes by fiscal year, provider (obstetrician vs. non-obstetrician), and institutional delivery volume (high, medium, low) was examined by introducing interaction terms into logistic regression mixed-effects models with a logit link function to account for clustered observations within institutions. The magnitude of absolute effects was quantified by calculating adjusted rate differences and the adjusted number needed to treat (NNT). The adjusted NNTs reflect the average number of operative vaginal deliveries that would have had to be delivered by Caesarean to avoid one case of the outcome of interest.
      Modification of the relationship between operative vaginal delivery and the outcomes of interest by pelvic station was assessed using the Breslow-Day chi-square test
      • Breslow NE
      • Day NE
      Statistical methods in cancer research, vol. I.
      for heterogeneity of OR. The significance of a linear trend in ORs across levels of pelvic station was determined using the Mantel-Haenszel chi-square test. The significance of trends in the rates of severe perineal lacerations by pelvic station was assessed using the Cochran-Armitage test for linear trend in proportions.
      Sensitivity analyses were carried out by estimating the association between attempted mode of delivery and composite perinatal and maternal morbidity and mortality by including failed forceps and vacuum attempts that resulted in Caesarean delivery in the attempted operative vaginal delivery category. The database did not include information on the sequence of instruments applied in deliveries with sequential instrumentation; however, because it is uncommon for vacuum to be applied following a failed forceps attempt, a second sensitivity analysis was carried out assuming that all sequential instrument applications involved a failed vacuum delivery attempt. All statistical analyses were performed using SAS software version 9.4 (SAS Institute, Cary, NC). The study was approved on December 3, 2012 by the University of British Columbia's Clinical Research Ethics Board (H12-0277).

      RESULTS

      There were 887 857 singleton term deliveries by operative vaginal or Caesarean deliveries during the study period. After exclusions (online Figure A.1), 61 106 singleton term deliveries with a prolonged second stage were included in the study, 38 013 with dystocia and 23 093 with fetal distress (Figure 1). Older women (≥35) and those who delivered at later gestational ages (39–41 weeks) were more likely to have had a Caesarean delivery. Midpelvic forceps was more commonly used in nulliparous women compared with vacuum, whereas vacuum delivery at all stations was more likely among parous women (Table 1). Macrosomic infants (>4000 g) were more likely to be delivered by Caesarean and less likely to be delivered by vacuum extraction.
      Fig 1
      Figure 1Cohort of deliveries with prolonged second stage of labour stratified by indication for operative delivery, success or failure of operative vaginal delivery (OVD) attempt, and operative instrument.
      Table 1Frequency of mode of delivery by maternal and infant characteristic and obstetric factors among women delivering term singletons by operative delivery with prolonged second stage of labour, Canada (excluding Quebec), 2003-2013 (N = 55 450)
      Caesarean deliveryOperative vaginal delivery
      Characteristicn = 15 034 n (%)Forceps n = 15 565 n (%)Vacuum n = 24 851 n (%)P value
      Maternal age<0.0001
       <20444 (21.6)484 (23.5)1128 (54.9)
       20–241810 (23.9)1974 (26.1)3783 (50.0)
       25–294645 (26.2)4956 (27.9)8158 (45.9)
       30–345388 (28.4)5490 (29.0)8075 (42.6)
       35–392310 (29.7)2294 (29.5)3166 (40.7)
       ≥40437 (32.5)367 (27.3)541 (40.2)
      Parity<0.0001
       08475 (26.1)9003 (27.8)14 963 (46.1)
       11078 (25.3)953 (22.4)2227 (52.3)
       ≥2236 (25.0)160 (17.0)547 (58.0)
       Missing5245 (29.5)5449 (30.6)7114 (39.9)
      Gestational age (weeks)<0.0001
       37–382297 (25.0)2604 (28.3)4290 (46.7)
       39–4112 737 (27.5)12 961 (28.0)20 561 (44.4)
      Birth weight (g)<0.0001
       <3000936 (18.7)1409 (28.1)2666 (53.2)
       3000–399910 603 (25.8)11 752 (28.5)18 822 (45.7)
       ≥40003495 (37.7)2404 (26.0)3363 (36.3)
      Institutional delivery volume<0.0001
       Low4486 (24.4)4317 (23.5)9581 (52.1)
       Medium4762 (26.7)4636 (25.9)8469 (47.4)
       High5786 (30.1)6612 (34.4)6801 (35.4)
      Provider<0.0001
       Obstetrician14 401 (30.2)14 990 (31.4)18 279 (38.3)
       Non-obstetrician633 (8.1)575 (7.4)6572 (84.5)
      Indication<0.0001
       Dystocia9300 (26.9)9648 (27.9)15 614 (45.2)
       Fetal distress5734 (27.5)5917 (28.3)9237 (44.2)
      Overall, the rates of composite severe perinatal and maternal morbidity and mortality were 0.83% and 1.31%, respectively, in deliveries with dystocia. These rates were higher in deliveries with fetal distress (1.83% and 1.46%, respectively).

      Severe Perinatal Morbidity and Mortality

      The rate of severe perinatal morbidity and mortality in the Caesarean delivery group was 0.66% in deliveries with dystocia and 1.80% in deliveries with fetal distress. Among women with dystocia, forceps delivery and vacuum delivery were associated with higher rates of severe perinatal morbidity and mortality compared with Caesarean delivery (forceps: aOR 1.56; 95% CI 1.13–2.17; NNT 272; vacuum: aOR 1.44; 95% CI 1.06–1.97; NNT 346) (Table 2). Stratification by pelvic station showed positive associations between outlet, low, and midpelvic forceps and severe perinatal morbidity and mortality; however, the association was significant only at midpelvic station (outlet: aOR 1.77; 95% CI 0.76–4.13; low: aOR 1.38; 95% CI 0.92–2.06; midpelvic: aOR 1.74; 95% CI 1.18–2.58). The same positive associations with perinatal morbidity and mortality were shown in vacuum deliveries at all levels of pelvic station, but it was only at low station that the association was significant (outlet: aOR 1.35; 95% CI 0.79–2.30; low: aOR 1.54; 95% CI 1.05–2.26; midpelvic: aOR 1.62; 95% CI 0.98–2.67) (Table 2). Nonetheless, aORs for composite perinatal morbidity and mortality were not significantly different among outlet versus low versus midpelvic deliveries by forceps (aOR 1.77 vs. 1.38 vs. 1.74, respectively, P = 0.34) or vacuum (1.35 vs. 1.54 vs. 1.62, respectively, P = 0.43). Among deliveries with fetal distress, there was no significant difference in rates of severe perinatal morbidity and mortality with forceps or vacuum delivery at any pelvic station compared with Caesarean delivery (Table 3, online Figure A.2).
      Table 2Rates, adjusted ORs, and 95% CIs for perinatal and maternal outcomes by mode of delivery and pelvic station among term singleton deliveries with prolonged second stage and dystocia, Canada (excluding Quebec), 2003-2013
      All models are adjusted for maternal age, parity, birth weight, province, and fiscal year of birth. Bold text denotes statistically significant associations.
      OutcomeCaesarean deliveryn = 9300ForcepsVacuum
      All stationsn = 9648Outletn = 549Lown = 4901Midpelvicn = 4198All stationsn = 15 614Outletn = 2344Lown = 5191Midpelvicn = 2158NOSn = 5921
      Severe perinatal morbidity and mortality%aOR (95% CI)0.66Ref0.931.56 (1.13–2.17)1.091.77 (0.76–4.13)0.821.38 (0.92–2.06)1.051.74 (1.18–2.58)0.861.44 (1.06–1.97)0.771.35 (0.79–2.30)0.921.54 (1.05–2.26)1.021.62 (0.98–2.67)0.791.32 (0.89–1.95)
      Severe birth trauma%aOR (95% CI)0.17Ref0.684.64 (2.68–8.03)0.916.12 (2.22–16.9)0.553.81 (2.04–7.10)0.815.35 (2.94–9.74)0.493.35 (1.94–5.77)0.382.72 (1.19–6.20)0.523.49 (1.87–6.51)0.603.61 (1.71–7.61)0.473.35 (1.80–6.25)
      Birth trauma%aOR (95% CI)2.09Ref5.973.24 (2.74–3.82)7.294.04 (2.83–5.77)5.393.10 (2.56–3.75)6.483.28 (2.71–3.96)8.044.11 (3.52–4.80)6.613.47 (2.79–4.32)7.763.96 (3.32–4.72)10.844.54 (3.71–5.55)7.824.33 (3.63–5.15)
      Severe maternal morbidity and mortality%aOR (95% CI)1.65Ref1.531.03 (0.81–1.29)0.910.58 (0.24–1.42)1.470.96 (0.72–1.27)1.691.17 (0.88–1.56)0.980.64 (0.51–0.81)0.980.62 (0.40–0.97)0.850.56 (0.40–0.79)1.110.74 (0.48–1.15)1.050.69 (0.51–0.93)
      Obstetric trauma%aOR (95% CI)6.33Ref24.95.34 (4.85–5.88)19.34.08 (3.24–5.14)25.65.41 (4.86–6.02)24.85.40 (4.84–6.04)15.02.89 (2.63–3.18)12.82.36 (2.04–2.74)15.52.91 (2.60–3.26)17.33.35 (2.90–3.86)14.62.92 (2.61–3.27)
      Severe perineal laceration (third- or fourth-degree)% (95% CI)<0.0521.9 (21.1–22.8)18.4 (15.4–21.9)23.0 (21.9–24.2)21.1 (19.9–22.4)13.9 (13.3–14.4)11.5 (10.3–12.8)14.5 (13.5–15.5)15.8 (14.3–17.4)13.5 (12.7–14.4)
      CI: confidence interval; NOS: not otherwise specified; aOR: adjusted odds ratio; Ref: reference.
      a All models are adjusted for maternal age, parity, birth weight, province, and fiscal year of birth. Bold text denotes statistically significant associations.
      Table 3Rates, adjusted ORs, and 95% CIs for perinatal and maternal outcomes by mode of delivery and pelvic station among term singleton deliveries with prolonged second stage and fetal distress, Canada (excluding Quebec), 2003–2013
      All models are adjusted for maternal age, parity, birth weight, province, and fiscal year of birth. Bold text denotes statistically significant associations.
      OutcomeCaesarean deliveryn = 5734ForcepsVacuum
      All stations n = 5917Outlet n = 257Low n = 2944Midpelvic n = 2716All stationsn = 9237Outlet n = 1350Low n = 3516Midpelvic n = 1672NOS n = 2699
      Severe perinatal morbidity and mortality%aOR (95% CI)1.80Ref1.941.14 (0.87–1.49)0.780.44 (0.11–1.79)1.831.07 (0.77–1.50)2.171.27 (0.92–1.77)1.781.03 (0.80–1.32)1.410.78 (0.48–1.29)1.821.06 (0.77–1.45)1.971.20 (0.80–1.81)1.781.02 (0.72–1.45)
      Severe birth trauma%aOR (95% CI)0.16Ref0.886.68 (3.28–13.6)0.393.00 (0.38–23.9)0.584.51 (2.00–10.2)1.259.29 (4.42–19.5)0.705.25 (2.60–10.6)0.443.31 (1.17–9.39)0.685.29 (2.44–11.5)1.148.11 (3.59–18.3)0.594.50 (1.96–10.3)
      Birth trauma%aOR (95% CI)2.69Ref7.152.97 (2.45–3.59)5.842.75 (1.58–4.77)6.112.77 (2.22–3.46)8.393.15 (2.55–3.90)8.513.35 (2.80–4.00)5.482.24 (1.68–2.98)8.023.08 (2.51–3.78)13.34.34 (3.48–5.40)7.673.55 (2.85–4.42)
      Severe maternal morbidity and mortality%aOR (95% CI)2.18Ref1.590.77 (0.59–1.01)2.331.14 (0.49–2.62)1.460.73 (0.51–1.04)1.660.78 (0.55–1.10)0.930.43 (0.32–0.57)0.960.43 (0.24–0.77)0.820.38 (0.25–0.58)1.140.52 (0.31–0.85)0.930.43 (0.28–0.67)
      Obstetric trauma%aOR (95% CI)8.09Ref26.34.23 (3.78–4.73)27.24.70 (3.50–6.30)27.64.50 (3.97–5.11)24.73.90 (3.42–4.44)16.02.28 (2.04–2.55)15.82.22 (1.86–2.65)16.02.22 (1.95–2.54)17.82.50 (2.13–2.94)15.02.23 (1.93–2.57)
      Severe perineal laceration (third- or fourth-degree)% (95% CI)<0.0922.8 (21.8–23.9)25.3 (20.4–30.9)24.5 (23.0–26.1)20.8 (19.3–22.4)14.9 (14.2–15.7)14.8 (13.0–16.8)14.7 (13.6–15.9)16.2 (14.5–18.0)14.5 (13.2–15.9)
      CI: confidence interval; NOS: not otherwise specified; aOR: adjusted odds ratio; Ref: reference.
      a All models are adjusted for maternal age, parity, birth weight, province, and fiscal year of birth. Bold text denotes statistically significant associations.

      Severe Maternal Morbidity and Mortality

      The rate of severe maternal morbidity and mortality in the Caesarean delivery group was 1.65% in deliveries with dystocia and 2.18% in deliveries with fetal distress. Forceps delivery was not associated with severe maternal morbidity and mortality among women with dystocia or fetal distress. However, vacuum delivery was associated with lower rates of severe maternal morbidity and mortality compared with Caesarean delivery (aOR 0.64; 95% CI 0.51–0.81 among women with dystocia; and aOR 0.43; 95% CI 0.32–0.57 among women with fetal distress) (Table 2, Table 3). The association between vacuum delivery and composite severe maternal morbidity and mortality was not modified by pelvic station (online Figure A.2).

      Birth Trauma

      Birth trauma and severe birth trauma were higher in both the forceps and vacuum groups when compared with Caesarean delivery, irrespective of indication. (Tables 2 and 3). Among women with fetal distress who were delivered by vacuum, the aOR for birth trauma was 2.24 at outlet station, 3.08 at low station, and 4.34 at midpelvic station. The association between forceps delivery and birth trauma was not modified by pelvic station (Figure 2A), whereas the association between vacuum delivery and birth trauma varied by pelvic station (P = 0.0002 among deliveries with dystocia and P < 0.0001 among deliveries with fetal distress). The adjusted rate differences for birth trauma following forceps delivery were 4.67 and 5.29 per 100 deliveries compared with Caesarean delivery for dystocia and fetal distress, respectively (NNTs of 21 and 19, respectively) (online Table A.2). Adjusted rate differences and NNTs for birth trauma following vacuum delivery were similar; NNTs for women with fetal distress were 30, 18, and 11 for outlet, low, and midpelvic vacuum, respectively (online Table A.2).
      Fig 2
      Figure 2Adjusted ORs and 95% CIs for (A) birth trauma, (B) obstetric trauma following forceps and vacuum delivery compared with Caesarean delivery, by pelvic station and indication, and (C) rates of severe perineal lacerations following forceps and vacuum delivery by pelvic station and indication, in term singleton deliveries with a prolonged second stage of labour, in Canada (excluding Quebec), 2003-2013.
      Asterisks denote a P value of <0.05 for chi-square tests for heterogeneity, trend in the ORs, or rates.

      Obstetric Trauma

      As with birth trauma, rates of obstetric trauma were higher among women with operative vaginal delivery compared with Caesarean delivery, especially with forceps (Figure 2B). For deliveries with dystocia, the associations between forceps and vacuum delivery and obstetric trauma were modified by pelvic station (P = 0.004 for vacuum and P = 0.0006 for forceps). There was a linear increase in the effect of vacuum delivery on obstetric trauma (aOR at outlet station: 2.36; aOR at low station: 2.91; and aOR at midpelvic station: 3.35, P for linear trend in OR < 0.0001) (Table 2). Among women with fetal distress, the effect of forceps and vacuum delivery on obstetric trauma was not significantly modified by pelvic station, (P = 0.10 for forceps and P = 0.16 for vacuum) (Figure 2B). The adjusted rate differences for forceps and vacuum delivery compared with Caesarean delivery are listed in online Table A.2. NNTs for obstetric trauma following forceps delivery ranged from three to five, whereas those for vacuum delivery ranged from seven to 12, depending on pelvic station and indication.
      Rates of severe perineal lacerations were high (11% to 25%) among all operative vaginal deliveries, regardless of pelvic station (Figure 2C). Among women with dystocia, the severe perineal laceration rate following forceps delivery was not affected by pelvic station. However, in the vacuum group, there was a positive linear trend in the rate of severe lacerations by station (Figure 2C). Among deliveries with fetal distress, severe perineal laceration rates were lower following forceps at midpelvic station compared with low and outlet forceps (P for linear trend = 0.0009). Rates of severe perineal lacerations stratified by laceration degree are listed in online Table A.3 and online Table A.4.

      Subgroup and Sensitivity Analyses

      Neither fiscal year nor type of practitioner (obstetrician vs. non-obstetrician) modified the relationship between mode of delivery and any of the study outcomes. However, the association between operative vaginal delivery and outcome was modified by institutional delivery volume. Among women with dystocia, the aOR for severe maternal morbidity and mortality following forceps delivery was significantly lower in institutions with a high delivery volume (aOR 0.90) compared with institutions with a medium delivery volume (aOR 1.51, P for interaction = 0.04) (online Table A.5). Among deliveries with fetal distress, the same trend was observed for the aORs for birth trauma, which were lower in high– versus medium–delivery volume institutions (P for interaction = 0.03). The association between operative vaginal delivery and obstetric trauma was dependent on institutional delivery volume, regardless of instrument or indication, with the lowest aORs in high-volume institutions (P for interaction < 0.001) (online Table A.5).
      Although adverse outcomes following failed operative vaginal delivery were substantially worse than outcomes following successful operative vaginal delivery, the inclusion of failed operative vaginal delivery attempts did not appreciably change the association between all operative vaginal delivery and any of the study outcomes when compared with Caesarean delivery (online Table A.6). Similarly, when sequential instrument application was included with vacuum delivery, there was no substantial change in the associations, although there was a consistent increase in the magnitude of the positive associations and a decrease in the magnitude of the negative associations. Finally, among deliveries with fetal distress, failed trials of vacuum followed by an attempted forceps delivery were associated with increased rates of severe perinatal morbidity and mortality, birth trauma, and obstetric trauma, compared with failed trials of vacuum followed by Caesarean delivery (online Table A.7).

      DISCUSSION

      Our study showed higher rates of severe perinatal morbidity and mortality following operative vaginal delivery compared with Caesarean delivery among women with dystocia, although this association was not seen among women with fetal distress. Rates of birth trauma and severe birth trauma were significantly increased following operative vaginal delivery compared with Caesarean delivery. Severe maternal morbidity and mortality rates were lower among women delivered by vacuum extraction compared with Caesarean delivery for both dystocia and fetal distress. However, rates of obstetric trauma were significantly increased following forceps and vacuum delivery compared with Caesarean delivery. Severe perineal laceration rates were high following operative vaginal delivery and were an important component of the obstetric trauma rate. Some of the effects of operative vaginal delivery were modified by the pelvic station at which the procedure was carried out, whereas other associations were not similarly affected.
      Among deliveries with dystocia, the increased rates of severe perinatal morbidity and mortality in deliveries associated with forceps and vacuum were driven mainly by the increased rate of severe birth trauma, the most common types of which were subaponeurotic hemorrhage (among vacuum deliveries) and severe injury to the peripheral nervous system (brachial plexus injury) (online Table A.8). Rates of severe birth trauma were also high following operative vaginal delivery among women with fetal distress, although this effect was matched by higher rates of assisted ventilation among women with fetal distress who delivered by Caesarean.
      Vacuum delivery was associated with a lower risk of severe maternal morbidity and mortality compared with Caesarean delivery by approximately one third in deliveries with dystocia and by more than one half in deliveries with fetal distress. This decrease can be attributed to the higher rates of sepsis and cardiac complications among women delivered by Caesarean (online Table A.8). Conversely, the rates of obstetric trauma were two- to four-fold higher following vacuum deliveries compared with Caesarean deliveries, and more than one in 10 women delivered by vacuum extraction had a severe perineal laceration. Although rates of sepsis and cardiac complications following forceps delivery were also lower than rates following Caesarean delivery, rates of severe postpartum hemorrhage were higher following forceps delivery (1.26% in forceps deliveries with dystocia, 1.23% in forceps deliveries with fetal distress) (Table A.8). Our results suggest that uterine atony is the major contributor to the higher rates of postpartum hemorrhage; however, increased rates of hemorrhage likely also reflect increased blood loss related to perineal and vaginal trauma.
      • Knight M
      • Callaghan WM
      • Berg C
      • et al.
      Trends in postpartum hemorrhage in high resource countries: a review and recommendations from the International Postpartum Hemorrhage Collaborative Group.
      The rate of severe perineal laceration was 18.4% (95% CI 15.4%–21.9%) following outlet forceps among women with dystocia. This rate was 25.3% (95% CI 20.4%–30.9%) among women with fetal distress. The accuracy of these rates is supported by a validation study
      • Joseph KS
      • Fahey J
      Validation of perinatal data in the Discharge Abstract Database of the Canadian Institute for Health Information.
      showing that third- and fourth-degree laceration codes in the Discharge Abstract Database have a sensitivity and specificity of 97.1% and 99.9%, respectively. High rates of severe perineal laceration following operative vaginal delivery, ranging from 14% to 45%, have been reported in previous studies.
      • Bashore RA
      • Phillips Jr, WH
      • Brinkman 3rd, CR
      A comparison of the morbidity of midforceps and cesarean delivery.
      • Dierker LJ
      • Rosen MG
      • Thompson K
      • et al.
      The midforceps: maternal and neonatal outcomes.
      ,
      • Hagadorn-Freathy AS
      • Yeomans ER
      • Hankins GD
      Validation of the 1988 ACOG forceps classification system.
      ,
      • Friedman T
      • Eslick G
      • Dietz H
      Instrumental delivery and OASI.
      • Gossett DR
      • Gilchrist-Scott D
      • Wayne DB
      • et al.
      Simulation training for forceps-assisted vaginal delivery and rates of maternal perineal trauma.
      • Miller ES
      • Barber EL
      • McDonald KD
      • et al.
      Association between obstetrician forceps volume and maternal and neonatal outcomes.
      • Gurol‐Urganci I
      • Cromwell D
      • Edozien L
      • et al.
      Third‐and fourth‐degree perineal tears among primiparous women in England between 2000 and 2012: time trends and risk factors.
      • Johnson JH
      • Figueroa R
      • Garry D
      • et al.
      Immediate maternal and neonatal effects of forceps and vacuum-assisted deliveries.
      Operative vaginal delivery is an established risk factor for severe perineal laceration,
      • Lowder JL
      • Burrows LJ
      • Krohn MA
      • et al.
      Risk factors for primary and subsequent anal sphincter lacerations: a comparison of cohorts by parity and prior mode of delivery.
      • Mikolajczyk RT
      • Zhang J
      • Troendle J
      • et al.
      Risk factors for birth canal lacerations in primiparous women.
      and it is known to increase the risk of pelvic floor disorders in the 5 to 10 years after a first delivery.
      • Handa VL
      • Blomquist JL
      • McDermott KC
      • et al.
      Pelvic floor disorders after childbirth: effect of episiotomy, perineal laceration, and operative birth.
      Such high rates are concerning because severe perineal laceration can result in significant morbidity, including infection, incontinence, chronic pain, and loss of sexual function.
      • Lowder JL
      • Burrows LJ
      • Krohn MA
      • et al.
      Risk factors for primary and subsequent anal sphincter lacerations: a comparison of cohorts by parity and prior mode of delivery.
      • Dudding TC
      • Vaizey CJ
      • Kamm MA
      Obstetric anal sphincter injury: incidence, risk factors, and management.
      ,
      • Kammerer-Doak D
      • Rogers RG
      Female sexual function and dysfunction.
      Issues related to the increased risk of anal sphincter trauma following operative vaginal delivery, and relevant long-term quality-of-life implications, should be carefully discussed with women considering operative vaginal delivery.
      The strengths of our study include the use of a comprehensive database that included information on approximately 98% of births in Canada (excluding Québec).
      • Wen SW
      • Liu S
      • Marcoux S
      • et al.
      Uses and limitations of routine hospital admission/separation records for perinatal surveillance.
      The restriction of the study population to women with a prolonged second stage ensured that the comparison between operative vaginal delivery and Caesarean delivery was clinically meaningful, and the stratification of operative vaginal delivery by pelvic station was an additional strength. The limitations of our study include an inability to account for the skill of the operator. It is possible that birth and obstetric trauma associated with operative vaginal delivery is restricted to less experienced operators. This could potentially explain the modification of the effect of operative vaginal delivery by hospital volume in our study. However, women delivering in hospital have little understanding of the relevant issues regarding expertise in operative vaginal delivery, and our data reflect the experience and skills of contemporary practitioners. We were limited by our inability to ascertain pelvic station in Caesarean deliveries. Because Caesarean delivery is more likely carried out at midpelvic versus outlet station, our contrasts may have favoured the Caesarean delivery group in the comparisons with outlet procedures. Conversely, at midpelvic station our estimates of the adverse effects of operative vaginal delivery likely represent underestimates of the true effect because some deliveries by Caesarean section would have been carried out with substantial descent of the fetal head.

      CONCLUSION

      Our study shows that operative vaginal delivery by forceps or vacuum among women with dystocia is associated with higher rates of severe perinatal morbidity, whereas vacuum delivery is associated with lower rates of severe maternal morbidity compared with Caesarean delivery. The risks of severe birth trauma and obstetric trauma are substantially higher following operative vaginal delivery compared with Caesarean delivery, and such risks vary significantly by pelvic station. Encouraging operative vaginal delivery as an alternative to Caesarean delivery without increasing skills in performance and in selecting candidates for such deliveries could result in increases in severe birth trauma and obstetric trauma. Consideration should be given to counselling women in the antepartum period about the risks of operative vaginal delivery and Caesarean delivery.

      Acknowledgements

      This study was funded by a Canadian Institutes of Health Research grant on severe maternal morbidity (MAH-15445). Dr. Muraca is the recipient of a Vanier Canada Graduate Scholarship. Dr. Joseph is supported by the BC Children's Hospital Research Institute and holds a Canadian Institutes of Health Research Chair in maternal, fetal, and infant health services research (APR-126338). Dr. Lisonkova is supported by a Scholar Award from the Michael Smith Foundation for Health Research. The funding source has no direct role in the study design; collection, analysis, or interpretation of data; the writing of the report; or the decision to submit. Data for this study were provided by the Canadian Institute for Health Information; however, the analyses, conclusions, and opinions expressed herein are those of the authors and not those of Canadian Institute for Health Information. All authors declare that they have received no support from any organization for the submitted work, they have no financial relationships with any organizations that might have an interest in the submitted work in the previous 3 years, and they have no other relationships or activities that could appear to have influenced the submitted work.

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