Maternal and Neonatal Morbidity After Attempted Operative Vaginal Delivery : Obstetrics & Gynecology

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Contents: Original Research

Maternal and Neonatal Morbidity After Attempted Operative Vaginal Delivery

Froeliger, Alizée MD, MPH; Mattuizzi, Aurélien MD; Madar, Hugo MD, MPH; Hamel, Jean-François MD, PhD; Bouchghoul, Hanane MD, PhD; Sentilhes, Loïc MD, PhD

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Obstetrics & Gynecology 139(5):p 833-845, May 2022. | DOI: 10.1097/AOG.0000000000004746

Operative vaginal delivery, an alternative for avoiding cesarean birth in the late second stage, enables vaginal birth for maternal or fetal indications.1–5 Operative vaginal delivery rates range from 3% to 15% worldwide,1,6–9 and its practice patterns vary widely, especially instrument choice among the vacuum, forceps, or spatulas (consisting of two independent solid blades not connected to each other, ie, without a fixed or sliding lock mechanism, and with a rounded cephalic curve).10 When operative vaginal delivery is necessary, operators must choose their instrument rapidly, based on the characteristics of the woman and her labor, clinical circumstances such as fetal head station and occipital position, local practices, and their own experience and skills.

Comparing guidelines from the United States,1 the United Kingdom,7 Australia and New Zealand,8 Canada,9 and France10 shows no consistent strategy for this choice.11 They all note that vacuum-assisted deliveries appear most likely to be associated with both neonatal trauma and failure, but maternal morbidity occurs more often after forceps or spatula deliveries, with elevated rates of severe perineal lacerations and vaginal trauma.1,11,12 Long-term outcomes, notably urinary or anal incontinence, do not appear to differ, although results are inconsistent.12

Previous studies of maternal or neonatal complications after operative vaginal delivery by instrument type have important limitations, including retrospective design, confounding bias without important details to permit adjustment, changes in practices over time, and no control for indication bias.13 Previous randomized controlled trials (RCTs) of vacuum compared with forceps delivery had methodologic weaknesses and relatively few participants and date from two or more decades ago.12 Although RCTs should provide the best evidence, ethical and feasibility considerations prevent their performance today. Observational prospective studies using appropriate statistical methods, thus, might be the best way to evaluate outcomes after operative vaginal delivery.

We therefore sought to assess severe maternal and neonatal morbidity after attempted operative vaginal delivery by instrument (vacuum vs forceps or spatulas) as primary endpoints, and urinary and anal incontinence symptoms at 6 months after attempted operative vaginal delivery as secondary endpoints. Propensity score analyses was used to minimize differences in measured covariates between the group and indication bias.


This ancillary prespecified analysis used data collected from a prospective cohort study from December 2008 to October 2013 at a French tertiary care university hospital with more than 4,000 deliveries annually. Designed primarily to assess the effect of fetal head station on short-term maternal and neonatal morbidity, it also prospectively analyzed maternal complications at 6 months: pelvic floor disorders, sexual dysfunction, and postpartum depressive symptoms.14–16

This study included all women with live singleton pregnancies in vertex presentation at term (37 weeks of gestation or more) and an attempted operative vaginal delivery, defined as the placement of at least one blade for forceps or spatula or an attempt to place a vacuum, regardless of whether delivery was ultimately vaginal or cesarean. Exclusion criteria were multiple gestations, a known congenital anomaly, noncephalic presentation, and small-for-gestational-age status, defined as birth weight less than the 10th percentile for gestational age on the Hadlock curves.17,18

Our study population comprised all women in the primary cohort for whom the instrument used for an operative vaginal delivery was known. All women received information about our study and consented to collection of their data. The Research Ethics Committee of the University of Angers, France, approved the study (no. 2008).

As previously reported14–16, the attending obstetrician decided to attempt an operative vaginal delivery and chose the instrument (forceps, Kiwi OmniCup vacuum, or Thierry's spatulas) and place of delivery (operating room or not). Operative vaginal deliveries were performed by either the attending obstetrician (with 5 or more years of experience with operative vaginal delivery) or the obstetric resident (with less than 5 years of such experience) under the supervision of an experienced obstetrician, always present in the delivery room. The attending obstetrician always chose the instrument used and determined whether they needed to check the instrument placement personally before traction. All women were offered epidural analgesia. The bladder was emptied by catheter before delivery. In accordance with French guidelines,10 and again at the attending obstetrician's discretion, fetal head position could be assessed by ultrasonogram if doubts remained after examination. Avoidance of rotational forceps-assisted deliveries (more than 90° rotation) was recommended; only vacuum instruments were recommended for rotation. Experienced obstetricians could perform midpelvic deliveries in appropriately selected cases. If operative vaginal delivery failed, the same resident performed the cesarean delivery under the same attending obstetrician's supervision.

The medical records of women with attempted operative vaginal delivery were assessed and discussed on working days at the daily morning staff meeting. Attending obstetricians regularly reviewed with residents the American College of Obstetricians and Gynecologists’ classification of fetal head station,1 academic knowledge about operative vaginal delivery, and the clinical practice guidelines for this type of delivery, issued by the French National College of Obstetricians and Gynecologists.10Station was defined as the level of the leading bony point of the fetal head in centimeters at or below the level of maternal ischial spines (0 and +1, midpelvic; +2 and +3, low; +4 and +5, outlet).1 Indications for attempted operative vaginal delivery included nonreassuring scalp pH and fetal heart rate abnormalities (defined as prolonged deceleration, bradycardia, or decreased variability)19 or prolongation of the second-stage pushing phase owing to inadequate expulsive efforts or failure to progress.10,20 All women underwent continuous fetal heart rate monitoring. Episiotomy, always mediolateral, was at the practitioner's discretion. A pediatrician always examined the newborn within 2 hours after delivery. These clinical procedures have been reported previously.14,21

The midwife or obstetrician and pediatrician responsible for the delivery and the neonate prospectively collected details of procedures used to manage the labor and all clinical outcomes identified during the immediate postpartum period. Other short-term data were collected by a research assistant, independent of the local medical team, from a prospectively maintained database of women who underwent attempted (or completed) operative vaginal delivery. Intermediate-term data of pelvic floor disorders were prospectively collected from a questionnaire sent 6 months after delivery. A second mailing was sent to the women who did not respond to the first.14–16

The primary endpoints were composite variables of severe maternal and neonatal morbidity. Severe short-term maternal morbidity was defined as at least one of the following: third- or fourth-degree perineal laceration, perineal hematoma, cervical laceration, uterine incision extension during cesarean delivery, postpartum hemorrhage exceeding 1,500 mL (blood loss was routinely assessed with a collector bag placed just after birth),22,23 surgical hemostatic procedures, uterine artery embolization, blood transfusion, infection (endometritis, episiotomy infection, or wound infection requiring surgery), thromboembolic events, admission to the intensive care unit, and maternal death.14

Severe neonatal morbidity was defined as at least one of the following: 5-minute Apgar score less than 7, umbilical artery pH less than 7.0 (umbilical artery blood gas values were routinely measured), need for resuscitation or intubation, neonatal trauma, intraventricular hemorrhage greater than grade 2, neonatal intensive care unit admission exceeding 24 hours, convulsions, sepsis, and neonatal death.14

The secondary endpoints were pelvic floor disorders at 6 months after delivery, assessed as described in Appendix 1, available online at Urinary incontinence (UI) was assessed by the French version of the Bristol Female Lower Urinary Tract Symptoms validated questionnaire24–26 about the frequency, amount, and circumstances of leakage and whether and how much UI bothered women. Anal incontinence (AI) was assessed with the French version of the American Society of Colon and Rectal Surgeons’ FISI (Fecal Incontinence Severity Index),27,28 based on type of incontinence and frequency matrix. A high FISI score indicated severe perceived symptoms.

Our exposure variable was the type of instrument used for the attempted operative vaginal delivery, classified into two groups: vacuum and forceps or spatulas. Analysis considered the last instrument used when two were used sequentially.

All variables that might influence both instrument choice and the endpoints were considered potential confounding variables and used as adjustment variables. They included maternal baseline characteristics such as age, prepregnancy body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) based on prepregnancy height and weight, parity, history of cesarean delivery, adverse events during previous delivery (birth weight greater than 4,000 g, shoulder dystocia, operative vaginal delivery, third- or fourth-degree perineal laceration, or postpartum hemorrhage greater than 1,500 mL); and characteristics of pregnancy, labor, and delivery, such as diabetes mellitus during pregnancy (preexisting or gestational), gestational weight gain, prenatally suspected macrosomia (determined by fundal height measurement at delivery greater than 37 cm or ultrasonographic fetal abdominal circumference greater than the 90th percentile for gestational age on Hadlock curves17,18), gestational age at delivery (determined by craniocaudal length at a first-trimester ultrasonographic examination or the date of the last menstrual period, a second- or third-trimester ultrasonogram, or both if no first-trimester ultrasonogram was performed),29 type of labor (spontaneous or induced by prostaglandins, amniotomy, or oxytocin), epidural analgesia, fetal head position (occiput anterior, posterior, or transverse), duration of the second stage of labor (complete dilatation to birth) and of the active second stage (from the beginning of expulsive efforts to birth [pushing time]), indication for attempted operative vaginal delivery, station at attempted delivery by the American College of Obstetricians and Gynecologists’ classification,1 and operator for delivery (attending obstetrician or resident).

Continuous variables were described by their means and SDs or medians and interquartile ranges, as appropriate, and compared between groups by Student’s t test or Kruskal-Wallis test. Categorical variables were described by proportions and compared using χ2 or Fisher exact tests, as appropriate. To control for confounding factors that might influence both the choice of instrument and the endpoints, we began with logistic regression models with multiple adjustments to estimate crude and adjusted odds ratios (aORs) and their 95% CIs. We used theoretical hypotheses to select potential confounders for the multivariable analysis and interaction terms between modes of delivery and the covariates considered to test for clinically relevant interactions. Because instrument choice was probably guided by characteristics of the women and their pregnancies and labors, rather than chance, we used a propensity score as a sensitivity analysis to limit potential indication bias.30 Women's propensity scores were defined as their probability of undergoing attempted operative vaginal delivery by forceps or spatulas, based on their individual covariates measured before delivery. A 1:1 matching algorithm was used within a caliper of 0.2 SD of the logit of the propensity score30,31 to match women for the selected baseline maternal and obstetric characteristics. We checked imbalances after matching by propensity score distribution and standardized mean differences.32 In the matched set, paired conditional generalized estimating equation logistic regression was used to estimate odds ratios (ORs) and their 95% CIs to quantify the association between instrument type and short-term severe maternal and neonatal morbidity. The same procedures were used for the secondary endpoints. Appendix 2, available online at, details the propensity score construction and matching procedures. A sensitivity analysis used multiple imputation of missing data. The proportion of women with missing data for any covariate included in the main multivariable model ranged from 1% to 5% for primary endpoints and from 1% to 8% for secondary endpoints. We performed multiple imputation chained equations for the missing data and pooled estimates according to Rubin's rules (10 data sets imputed).33 Differences were considered significant at P<.05. Stata SE 15 was used for all analyses.


During the study period, the hospital had 19,786 deliveries: 15,836 (80.0%) vaginal deliveries, including 2,153 (13.6%) successful operative vaginal deliveries, and 3,950 (20.0%) cesarean deliveries, including 39 (0.2% of all deliveries and 1% of all cesarean deliveries) after failed operative vaginal delivery. This study analyzed the 2,192 deliveries with attempted operative vaginal delivery (98.2% successful and 1.8% failed) but first excluded 54 women meeting exclusion criteria (14 twin pregnancies, 26 preterm deliveries [less than 37 weeks of gestation], and 14 small-for-gestational-age newborns) and 10 for missing data about the instrument used. Our final sample for the main analysis comprised 2,128 births with attempted operative vaginal delivery: 654 (30.7%) by vacuum and 1,474 (69.3%) by forceps or spatulas (Fig. 1).

Fig. 1.:
Study flow chart.

Table 1 shows maternal and labor characteristics by type of instrument. Nulliparity, prenatally suspected macrosomia, induced labor, second stage of labor exceeding 3 hours, high oxytocin doses, epidural analgesia, manual rotation of the presentation, persistent occiput posterior position, midpelvic delivery, and attempted delivery by the attending senior obstetrician were significantly more frequent in forceps- or spatula-assisted deliveries (Table 1).

Table 1.:
Maternal and Labor Characteristics for Operative Vaginal Deliveries by Instrument (N=2,128)

Table 2 shows maternal and neonatal morbidity by instrument. The severe maternal morbidity rate after attempted operative vaginal delivery was 5.4% (n=35, 95% CI 3.8–7.4) with vacuum and 10.5% (n=154, 95% CI 8.3–12.1) with forceps or spatulas. It differed significantly between the groups (P<.001) (Table 2). In the univariate analysis, women with severe morbidity more often had higher mean prepregnancy BMIs, previous cesarean deliveries and operative vaginal deliveries, prenatally suspected macrosomia, median oxytocin doses, cesarean delivery after failed attempted operative vaginal delivery, and delivery performed by a senior attending obstetrician (Table 3). The severe maternal morbidity rate was higher among operative vaginal deliveries attempted with forceps or spatulas than with vacuum in the univariate analysis (crude OR 2.06, 95% CI 1.41–3.01) and the multivariable logistic regression analysis (aOR 1.99, 95% CI 1.27–3.10), after adjustment for potential confounders (Appendix 3, available online at These results were consistent with the first sensitivity analysis based on multiple imputation (aOR 1.93, 95% CI 1.25–2.99) (Fig. 2A).

Table 2.:
Maternal and Neonatal Outcomes for Operative Vaginal Deliveries by Instrument (N=2,128)
Table 3.:
Univariate Analysis of Severe Maternal and Neonatal Morbidity After Attempted Operative Vaginal Delivery by Instrument (N=2,128)
Fig. 2.:
Severe maternal and neonatal morbidity (A) and pelvic floor disorders at 6 months (B) after attempted operative vaginal delivery by instrument (reference: vacuum). OR, odds ratio.

The rate of severe neonatal morbidity after attempted operative vaginal delivery was 8.4% (n=55, 95% CI 6.4–10.8) with vacuum and 10.2% (n=155, 95% CI 8.7–11.8) with forceps or spatulas and did not differ significantly between the groups (Table 2) in either the univariate (crude OR 1.23, 95% CI 0.89–1.71) or multivariable (aOR 1.04, 95% CI 0.69–1.56) analyses (Appendix 3, These results were consistent with the first sensitivity analysis based on multiple imputation (aOR 1.10, 95% CI 0.74–1.65) (Fig. 2A).

The propensity score–matching process analyzed 594 cases: 297 matched deliveries in each group, including 45.4% of the attempted operative vaginal deliveries with vacuum and 20.1% of those with forceps or spatulas. The two matched groups were well balanced for all variables (Appendix 4, available online at In the propensity score–matched groups, the rates of severe maternal morbidity were 5.7% (n=17) with vacuum and 10.4% (n=31) with forceps or spatulas, and the rates of severe neonatal morbidity were 9.4% (n=28) with vacuum and 10.1% (n=30) with forceps or spatulas. After propensity score matching, attempted operative vaginal delivery with forceps or spatulas was no longer associated with a higher rate of severe maternal (aOR 1.46, 95% CI 0.72–2.95) or neonatal (aOR 1.08, 95% CI 0.63–1.85) morbidity (Fig. 2A).

Six months after delivery, 934 women (43.9%) among the 2,128 who had an attempted operative vaginal delivery completed the questionnaires: 276 (29.5%) had undergone attempted operative vaginal delivery by vacuum and 658 (70.5%) by forceps or spatulas (P=.3).

Respondents and nonrespondents differed on several characteristics. Nonrespondents were younger, and more of them had gestational weight gains greater than 20 kg, sequential use of two instruments, and severe neonatal morbidity (11.5% vs 7.5%; P=.002); fewer had a prolonged second stage of labor and epidural analgesia. The type of instrument used for attempted operative vaginal delivery did not differ between respondents and nonrespondents (Appendix 5, available online at

Table 2 shows pelvic floor disorders 6 months after delivery by instrument. Among women with attempted operative vaginal delivery, the prevalence of UI symptoms at 6 months was 22.7% (212/933, 95% CI 20.1–25.5) and the prevalence of AI symptoms was 22.0% (202/918, 95% CI 19.4–24.8); 13.7% (127/924, 95% CI 11.6–16.1) reported perineal pain. Urinary incontinence symptoms (19.6% for women with vacuum-assisted delivery and 24.1% for those with forceps- or spatula-assisted delivery), AI symptoms (19.2% vs 23.2%, respectively), and perineal pain (11.6% vs 14.6%) did not differ significantly between these groups. Similarly, the median [interquartile range] FISI score in women with AI did not differ between these two groups (11 [7–12] vs 11 [7–16], respectively; P=.3) (Table 2). Characteristics significantly associated or not with UI or AI at 6 months are shown in Appendix 6 (available online at

Operative vaginal delivery attempted with forceps or spatulas compared with vacuum was not significantly associated with a higher rate of UI, either in multivariable analysis (aOR 1.44; 95% CI 0.90–2.30) (Appendix 7, available online at, after multiple imputation (aOR 1.47 95% CI 0.95–2.29) or after propensity score matching (aOR 1.57 95% CI 0.85–2.89) (Fig. 2B). Inversely, it was significantly associated with a higher rate of AI in the multivariable logistic regression analysis (aOR 1.67, 95% CI 1.04–2.72) (Appendix 7, The first sensitivity analysis, using multiple imputation, reached a similar result (aOR 1.53, 95% CI 1.00–2.35), but no difference remained after propensity score matching (aOR 1.76, 95% CI 0.96–3.24) (Fig. 2B). The propensity score–matching process analyzed 248 cases for UI and 242 for AI, and the matched groups for each analysis were well balanced for all variables (Appendix 8, available online at


Our results, after controlling for indication bias by propensity score analysis, suggest that, among women with singleton term pregnancies, attempted operative vaginal delivery with forceps or spatulas compared with vacuum was not associated with greater severe maternal or neonatal morbidity or with higher rates of UI and AI symptoms at 6 months postpartum. A Cochrane Review examined 32 RCTs of attempted operative vaginal delivery by different instruments, including 3,338 women from 13 trials, performed mainly before 2000 (n=10) and comparing forceps with vacuum delivery. Forceps were more often associated with maternal morbidity, especially for third- and fourth-degree perineal tears (relative risk [RR] 1.89, 95% CI 1.51–2.37), vaginal trauma (RR 2.48, 95% CI 1.59–3.87), and flatus incontinence or impaired continence (RR 1.77, 95% CI 1.19–2.62). Vacuum-assisted deliveries were associated with a higher rate of failed vaginal birth and a trend toward higher neonatal morbidity.12 All had notable methodologic limitations: small (median 210 participants, range 36–637), single-center studies, some only quasi-randomized, and mostly underpowered to assess adverse events.

Observational studies have reported discordant results regarding the association between maternal and neonatal morbidity and forceps-, spatula- and vacuum-assisted deliveries. They also were limited by methodologic flaws including small sample size, retrospective design, limited data quality and availability, and absence of propensity score analysis to limit the indication bias affecting choice of instrument.4,34–38 Any statistical approaches were limited to multivariable analyses controlling for some potential confounders. In these cases, results were consistent with our adjusted OR showing higher maternal morbidity with forceps-assisted delivery than with vacuum-assisted delivery.13

Unlike most studies, ours has the advantage of using propensity score analysis to compare attempted operative vaginal delivery results among women with the same distribution of baseline covariates, that is, the same probability of forceps-assisted delivery. Moreover, our study provides prospective and longitudinal information about maternal outcomes, with detailed characteristics about several potential confounders to ensure appropriate adjustment.

Choice of instrument for operative vaginal delivery remains controversial. Previous data suggest conflict between the mother's and fetus's interests: forceps appear to be associated with maternal morbidity and vacuum with more frequent and severe neonatal complications. Our study, using propensity score analysis to limit indication bias, shows no difference between vacuum and forceps or spatulas in maternal and neonatal morbidity until hospital discharge or in pelvic floor disorders at 6 months. The choice of instrument should be determined principally by the operator's or woman's preference. Future exploratory studies should assess whether some circumstances or subgroups of women might benefit from one instrument or the other and which determinants are associated with severe maternal and neonatal morbidity when operative vaginal deliveries are performed.

Our study has several strengths. First, the data come from a large, prospective cohort in a center with a policy of planned vaginal delivery, demonstrated indirectly by its operative vaginal delivery (13.6%) and cesarean delivery (20%) rates. These prospectively collected data, often unavailable in retrospective population-based studies, include maternal and obstetric characteristics, notably during the second stage of labor, and describe clinical situations affecting attempted operative vaginal delivery decisions (eg, prenatally suspected macrosomia, fetal head station, and occiput position). Second, these data are robust: a collector bag was routinely used to estimate blood loss after delivery, neonatal arterial blood gases were systematically measured, and a qualified neonatologist examined all neonates. Our previous results were consistent with other well-established findings, especially for short-term and midterm maternal morbidity and short-term neonatal morbidity after vacuum or forceps deliveries.14,15,21 Third, we studied all attempted operative vaginal deliveries, including failures, because their exclusion might mask a negative effect.3 Fourth, to control for indication bias (which would otherwise be this study's major limitation), we performed propensity score analysis, which appears to perform better than logistic regression in reducing the effects of confounding in observational studies.30,31 We rigorously adjusted for confounding factors, specifically maternal and obstetric characteristics (including prenatally suspected macrosomia, fetal head station, occiput position, and physician experience with attempted operative vaginal delivery and its indications) to minimize the likelihood of incorrectly attributing an association to forceps or spatulas. Our univariate analysis showed that forceps or spatulas were used in the most difficult conditions and vacuum for less complicated, lower-risk deliveries.

Our study has some limitations. First, despite our careful statistical approaches with sensitivity and multivariable and propensity score analyses, unmeasured confounders may persist. An RCT would undeniably be the best study design to compare the effects of the instrument used for attempted operative vaginal delivery, but its feasibility today seems doubtful. Second, the response rate at 6 months was only 43.9%. It is nonetheless similar to other studies assessing postpartum pelvic floor disorders by mailed questionnaire after birth.39–41 Although respondents and nonrespondents differed on some characteristics, nothing suggests that this potential selection bias produces a higher or lower risk of pelvic floor disorders. Moreover, the nonrespondents differed mainly on severe neonatal morbidity, a factor unrelated to UI or AI. Third, the low rate of neonatal morbidity, such as scalp hematoma, trauma, or seizures, limited our statistical power to detect potentially clinically meaningful differences between vacuum and forceps or spatulas. In addition, considering the small difference between the rates of severe neonatal morbidity (8.4% vs 10.2%), we acknowledge that our study is underpowered to confirm an absence of difference in neonatal adverse outcomes. Moreover, we must note that our results show a trend toward higher rates of short-term and long-term maternal morbidity, possibly obscured by the loss of power due to the propensity score matching and the exclusion of the unmatched women from that analysis. This may be aggravated for the maternal secondary outcomes assessed at 6 months by loss to follow-up. Nonetheless, this increase appears moderate. For immediate severe maternal morbidity, a post hoc calculation found that a sample size of 594 patients and 5–11% of deliveries with severe maternal morbidity would have yielded a power of 80% and an alpha of 0.05, able to detect an OR greater than 2.1 with univariate logistic regression. Lastly, UI and AI assessments at 6 months are considered the short term in the context of pelvic floor disorders; urogynecologic evaluation over the second year after the childbirth is considered more meaningful to patients and physicians.39,42–48

These limitations notwithstanding, in our study using propensity score methods to control for indication bias, attempted operative vaginal delivery managed by forceps or spatulas compared with vacuum was not associated with higher rates of severe maternal and neonatal morbidity or with maternal pelvic floor disorders. These results support the use of vacuum or forceps or spatulas, depending mainly on the operator's preference.


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