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Contraction of the levator ani muscle during Valsalva maneuver (coactivation) is associated with a longer active second stage of labor in nulliparous women undergoing induction of labor

Published:October 12, 2018DOI:https://doi.org/10.1016/j.ajog.2018.10.013

      Background

      The Valsalva maneuver is normally accompanied by relaxation of the levator ani muscle, which stretches around the presenting part, but in some women the maneuver is accompanied by levator ani muscle contraction, which is referred to as levator ani muscle coactivation. The effect of such coactivation on labor outcome in women undergoing induction of labor has not been previously assessed.

      Objective

      The aim of the study was to assess the effect of levator ani muscle coactivation on labor outcome, in particular on the duration of the second and active second stage of labor, in nulliparous women undergoing induction of labor.

      Study Design

      Transperineal ultrasound was used to measure the anteroposterior diameter of the levator hiatus, both at rest and at maximum Valsalva maneuver, in a group of nulliparous women undergoing induction of labor in 2 tertiary-level university hospitals. The correlation between anteroposterior diameter of the levator hiatus values and levator ani muscle coactivation with the mode of delivery and various labor durations was assessed.

      Results

      In total, 138 women were included in the analysis. Larger anteroposterior diameter of the levator hiatus at Valsalva was associated with a shorter second stage (r = –0.230, P = .021) and active second stage (r = –0.338, P = .001) of labor. Women with levator ani muscle coactivation had a significantly longer active second stage duration (60 ± 56 vs 28 ± 16 minutes, P < .001). Cox regression analysis, adjusted for maternal age and epidural analgesia, demonstrated an independent significant correlation between levator ani muscle coactivation and a longer active second stage of labor (hazard ratio, 2.085; 95% confidence interval, 1.158–3.752; P = .014). There was no significant difference between women who underwent operative delivery (n = 46) when compared with the spontaneous vaginal delivery group (n = 92) as regards anteroposterior diameter of the levator hiatus at rest and at Valsalva maneuver, nor in the prevalence of levator ani muscle coactivation (10/46 vs 15/92; P = .49).

      Conclusion

      Levator ani coactivation is associated with a longer active second stage of labor.

      Key words

      Click Supplemental Materials and Video under article title in Contents at ajog.org

      Introduction

      The second stage of labor is the defined as the duration from full cervical dilatation to delivery.

      National Institute for Health and Care Excellence. Intrapartum care for healthy women and babies, 2014. Clinical guideline [CG190]. Available at: https://www.nice.org.uk/guidance/cg190. Accessed September 20, 2018.

      Prolonged second stage of labor is associated with an increased risk of maternal and neonatal complications.
      • Laughon S.K.
      • Berghella V.
      • Reddy U.M.
      • Sundaram R.
      • Lu Z.
      • Hoffman M.K.
      Neonatal and maternal outcomes with prolonged second stage of labor.
      The length of the second stage of labor can be influenced by many factors. These may include fetal head dimensions, fetal weight, the use of epidural analgesia, and fetal head engagement.
      • Kamel R.
      • Youssef A.
      How reliable is fetal occiput and spine position assessment prior to induction of labor?.
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      • Cohen S.M.
      • Israel A.
      • et al.
      Sonographic large fetal head circumference and risk of cesarean delivery.
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      • Maroni E.
      • Youssef A.
      • et al.
      Sonographic pattern of fetal head descent: relationship with duration of active second stage of labor and occiput position at delivery.
      However, accurate prediction of the second stage duration, and the definition and management of a prolonged second stage of labor remain challenging.
      • Gimovsky A.C.
      • Berghella V.
      Randomized controlled trial of prolonged second stage: extending the time limit vs usual guidelines.

      Why was this study conducted?

      • Levator ani muscle contraction during Valsalva maneuver (coactivation) may represent an obstacle to spontaneous vaginal delivery. The effect of this phenomenon on labor outcome has not been studied previously.

      Key findings

      • Levator ani muscle contraction during Valsalva maneuver (coactivation) is associated with a significantly longer active second stage of labor. Larger diameters of the levator hiatus under Valsalva maneuver, but not at rest, are associated with shorter second and active second stage of labor.

      What does this add to what is known?

      • The effect of a new mechanism (namely levator ani muscle contraction during Valsalva; also known as coactivation) on the duration of the active second stage of labor.
      Valsalva maneuver, whereby the mother is asked to take a deep breath, hold the breath, and push downward when uterine contraction starts, is widely used in the management of the active second stage of labor. However, there is contradictory evidence concerning the benefit and harm in the use of this maneuver.
      • Yildirim G.
      • Beji N.K.
      Effects of pushing techniques in birth on mother and fetus: a randomized study.
      • de Tayrac R.
      • Letouzey V.
      Methods of pushing during vaginal delivery and pelvic floor and perineal outcomes: a review.
      • Prins M.
      • Boxem J.
      • Lucas C.
      • Hutton E.
      Effect of spontaneous pushing versus Valsalva pushing in the second stage of labor on mother and fetus: a systematic review of randomized trials.
      The Valsalva maneuver is normally accompanied by relaxation of the levator ani muscle, which stretches around the presenting part, but in some women the maneuver is accompanied by levator ani muscle contraction, which is referred to as levator ani muscle coactivation.
      • Orno A.K.
      • Dietz H.P.
      Levator co-activation is a significant confounder of pelvic organ descent on Valsalva maneuver.
      Vaginal delivery is one of the most important risk factors for pelvic floor dysfunction.
      • Jelovsek J.E.
      • Chagin K.
      • Gyhagen M.
      • et al.
      Predicting risk of pelvic floor disorders 12 and 20 years after delivery.
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      Pregnancy and parturition negatively impact vaginal angle and alter expression of vaginal MMP-9.
      • Handa V.L.
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      • Munoz A.
      Longitudinal study of quantitative changes in pelvic organ support among parous women.
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      • Milsom I.
      Factors influencing the incidence and remission of urinary incontinence after hysterectomy.
      • Lindo F.M.
      • Carr E.S.
      • Reyes M.
      • et al.
      Randomized trial of cesarean vs vaginal delivery for effects on the pelvic floor in squirrel monkeys.
      Transperineal ultrasound has been used extensively for assessment of the levator hiatus and levator ani muscle integrity
      • Dietz H.P.
      • Shek C.
      • Clarke B.
      Biometry of the pubovisceral muscle and levator hiatus by three-dimensional pelvic floor ultrasound.
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      • Delancey J.O.
      Interrater reliability and physical examination of the pubovisceral portion of the levator ani muscle, validity comparisons using MR imaging.
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      • den Boer D.J.
      • Mittal R.K.
      The reliability of puborectalis muscle measurements with 3-dimensional ultrasound imaging.
      • Dietz H.P.
      • Shek K.L.
      The quantification of levator muscle resting tone by digital assessment.
      • van Delft K.
      • Shobeiri S.A.
      • Thakar R.
      • Schwertner-Tiepelmann N.
      • Sultan A.H.
      Intra- and interobserver reliability of levator ani muscle biometry and avulsion using three-dimensional endovaginal ultrasonography.
      • Youssef A.
      • Montaguti E.
      • Sanlorenzo O.
      • et al.
      A new simple technique for 3-dimensional sonographic assessment of the pelvic floor muscles.
      • Youssef A.
      • Montaguti E.
      • Sanlorenzo O.
      • et al.
      Reliability of new three-dimensional ultrasound technique for pelvic hiatal area measurement.
      • Cyr M.P.
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      • Morin M.
      Pelvic floor morphometry and function in women with and without puborectalis avulsion in the early postpartum period.
      • Abdool Z.
      • Shek K.L.
      • Dietz H.P.
      The effect of levator avulsion on hiatal dimension and function.
      • DeLancey J.O.
      The hidden epidemic of pelvic floor dysfunction: achievable goals for improved prevention and treatment.
      • Dietz H.P.
      Pelvic floor ultrasound: a review.
      • Patel D.A.
      • Xu X.
      • Thomason A.D.
      • Ransom S.B.
      • Ivy J.S.
      • DeLancey J.O.
      Childbirth and pelvic floor dysfunction: an epidemiologic approach to the assessment of prevention opportunities at delivery.
      • Rahmanou P.
      • Caudwell-Hall J.
      • Kamisan Atan I.
      • Dietz H.P.
      The association between maternal age at first delivery and risk of obstetric trauma.
      and several studies have increased the understanding of the relationship between failure of vaginal delivery and pelvic floor dysfunction.
      • Abdool Z.
      • Shek K.L.
      • Dietz H.P.
      The effect of levator avulsion on hiatal dimension and function.
      • Dietz H.P.
      Pelvic floor ultrasound: a review.
      • Rahmanou P.
      • Caudwell-Hall J.
      • Kamisan Atan I.
      • Dietz H.P.
      The association between maternal age at first delivery and risk of obstetric trauma.
      • van Delft K.
      • Sultan A.H.
      • Thakar R.
      • Schwertner-Tiepelmann N.
      • Kluivers K.
      The relationship between postpartum levator ani muscle avulsion and signs and symptoms of pelvic floor dysfunction.
      • Youssef A.
      • Salsi G.
      • Cataneo I.
      • et al.
      Fundal pressure in second stage of labor (Kristeller maneuver) is associated with higher risk of levator ani muscle avulsion.
      Indeed, it has been suggested that the viscoelastic properties of the intact distal birth canal in healthy nulliparous women may predict the duration of the second stage of labor.
      • Tracy P.V.
      • Wadhwani S.
      • Triebwasser J.
      • et al.
      On the variation in maternal birth canal in vivo viscoelastic properties and their effect on the predicted length of active second stage and levator ani tears.
      However, the effect of levator ani muscle coactivation on labor outcome in women undergoing induction of labor has not been previously assessed.
      The aim of this study was to assess the effect of levator ani muscle coactivation on the outcome of labor, in particular on the duration of the second and active second stage of labor in nulliparous women undergoing induction of labor.

      Materials and Methods

      This was a prospective observational study conducted from November 2017 through May 2018 in 2 tertiary-level university hospitals (Sant'Orsola Malpighi University Hospital, University of Bologna and Kasr Al-Ainy University Hospital, Cairo University). The study population constituted a nonconsecutive series of nulliparous women with singleton pregnancies, fetuses in cephalic presentation, and no history of uterine surgery, undergoing induction of labor at 37–42 weeks of gestation for any indication. Pregnancies resulting in operative delivery for suspected fetal distress due to an abnormal fetal heart rate pattern in labor were excluded from the study, as it is unlikely that pelvic floor function may influence fetal condition. Women were recruited when one of the physicians involved in the study and experienced in transperineal ultrasound was present in the inpatient ward exclusively for the aim of the study.
      Following recruitment, an operator with >3 years of experience in transperineal ultrasound, blinded to clinical examination results, performed a transperineal ultrasound scan with a convex transducer covered by a sterile glove (Voluson 730 Expert or E10, GE Medical Systems, Zipf, Austria). In the midsagittal view the following structures were visualized: pubic symphysis, fetal head, rectum, and puborectalis muscle (Figure 1). The anteroposterior diameter of the levator hiatus, running from the inferior border of the symphysis pubis to the anterior border of the puborectalis muscle, which is the main portion of the levator ani muscle, was measured under resting condition and under maximum Valsalva maneuver (Figure 2). Levator ani muscle coactivation was diagnosed when the anteroposterior diameter of the levator hiatus under Valsalva maneuver was less than that in the resting state.
      • Orno A.K.
      • Dietz H.P.
      Levator co-activation is a significant confounder of pelvic organ descent on Valsalva maneuver.
      Figures 3 and 4 and Videoclip 1 illustrate the phenomenon of levator ani muscle coactivation.
      Figure thumbnail gr1
      Figure 1Technique of transperineal ultrasound showing structures on the midsagittal plane
      Technique of transperineal ultrasound. A, Placement of convex transducer in midsagittal plane. B, Ultrasound image. C, Structures visualized, including pubic symphysis (PS), urinary bladder (UB), fetal head, vagina (VAG), rectum (R), anus (A), and puborectalis muscle (P.R.).
      Kamel et al. Levator ani contraction and active second stage. Am J Obstet Gynecol 2019.
      Figure thumbnail gr2
      Figure 2Anteroposterior diameter of levator hiatus at rest and Valsalva maneuver
      Transperineal ultrasound images illustrating measurement of anteroposterior diameter of levator hiatus under A, resting condition and B, maximum Valsalva maneuver.
      Kamel et al. Levator ani contraction and active second stage. Am J Obstet Gynecol 2019.
      Figure thumbnail gr3
      Figure 3Valsalva maneuver associated with appropriate relaxation of the pelvic floor
      Valsalva maneuver associated with appropriate relaxation of pelvic floor. This can be demonstrated by increasing anteroposterior diameter of levator hiatus on 2-dimensional ultrasound images from A, rest to B, Valsalva, increasing hiatal area on 3-dimensional ultrasound using Omniview-VCI
      • Youssef A.
      • Montaguti E.
      • Sanlorenzo O.
      • et al.
      A new simple technique for 3-dimensional sonographic assessment of the pelvic floor muscles.
      • Youssef A.
      • Montaguti E.
      • Sanlorenzo O.
      • et al.
      Reliability of new three-dimensional ultrasound technique for pelvic hiatal area measurement.
      reconstruction from C, rest to D, Valsalva and E and F, on graphic illustration.
      Kamel et al. Levator ani contraction and active second stage. Am J Obstet Gynecol 2019.
      Figure thumbnail gr4
      Figure 4Valsalva maneuver associated with contraction of the pelvic floor (coactivation)
      Valsalva maneuver associated with levator ani muscle coactivation. This can be demonstrated by reduction of anteroposterior diameter of levator hiatus on 2- and 3-dimensional ultrasound images using Omniview-VCI
      • Youssef A.
      • Montaguti E.
      • Sanlorenzo O.
      • et al.
      A new simple technique for 3-dimensional sonographic assessment of the pelvic floor muscles.
      • Youssef A.
      • Montaguti E.
      • Sanlorenzo O.
      • et al.
      Reliability of new three-dimensional ultrasound technique for pelvic hiatal area measurement.
      (GE Healthcare, Zipf, Austria) reconstruction from A and C, rest to B and D, Valsalva and E and F, on graphic illustration.
      Kamel et al. Levator ani contraction and active second stage. Am J Obstet Gynecol 2019.
      Birth attendants were unaware of the results of transperineal ultrasound assessment. The second stage of labor was defined as the duration from full cervical dilatation to delivery, while the active second stage was calculated from the beginning of active maternal effort following confirmation of full dilatation of the cervix to delivery.

      National Institute for Health and Care Excellence. Intrapartum care for healthy women and babies, 2014. Clinical guideline [CG190]. Available at: https://www.nice.org.uk/guidance/cg190. Accessed September 20, 2018.

      Since there is insufficient evidence to justify routine use of any specific timing of pushing in the second stage, in both centers immediate and delayed pushing approaches were chosen according to women’s preference and comfort, and to the preference and experience of the birth attendant.
      • Lemos A.
      • Amorim M.M.
      • Dornelas de Andrade A.
      • de Souza A.I.
      • Cabral Filho J.E.
      • Correia J.B.
      Pushing/bearing down methods for the second stage of labor.
      In the 2 participating centers there is no policy to limit the time of second or active second stage of labor and the pushing technique, coached vs spontaneous, is left to the preference of the birth attendant.
      Following delivery, the medical records of the women were examined and the following data were extracted: maternal age and body mass index (BMI), gestational age, indication and method of induction of labor, use of epidural analgesia, mode of delivery, birthweight, interval between ultrasound assessment and delivery, and duration of second and active second stages of labor. The primary outcome of the present study was the duration of the second stage.

      Statistical analysis

      Differences between women with spontaneous vaginal delivery and the operative delivery group, and between women with and without coactivation, were assessed by unpaired 2-tailed Student t test and Fisher exact test. Pearson correlation was used to assess the significance of association between the anteroposterior diameter of the levator hiatus and various labor durations. The durations of induction of labor to delivery, and of second and active second stage were evaluated in relation to levator ani muscle coactivation using Cox regression analysis adjusted for identified significant confounders, and with Kaplan-Meier survival analysis.
      Considering the duration of the second stage as the primary outcome, an incidence of coactivation of 20%,
      • Orno A.K.
      • Dietz H.P.
      Levator co-activation is a significant confounder of pelvic organ descent on Valsalva maneuver.
      and based on recent unpublished data from a study on nulliparous women at term in Bologna University Hospital showing an average second stage duration of 60 ± 30 minutes, we calculated that a sample size of 135 women would be needed to exclude the null hypothesis that coactivation increases the second stage duration by 30%, considering an α of 0.05% and 80% power.
      The statistical analyses were performed using software (21.0 SPSS, Version; IBM Corp, Armonk, NY), and 2-tailed P values <.05 were considered statistically significant.
      The protocol of the study was approved by the local ethical committee of each participating hospital (reference number 139/2016/U/Oss in Bologna University Hospital and O18001 in Cairo University Hospital) and a consent form was signed by each eligible patient at the onset of labor. The study protocol coheres with the ethical guidelines of the World Medical Association Declaration of Helsinki–Ethical Principles for Medical Research Involving Human Subjects adopted by the 18th WMA General Assembly, Helsinki, Finland, June 1964 and amended by the 59th World Medical Association General Assembly, Seoul, South Korea, October 2008.

      Results

      In total, 161 women were recruited to the study, but 23 were excluded because of operative delivery for fetal distress. Demographic characteristics and data on labor and delivery for the 138 women (96 from Cairo University Hospital and 42 from Bologna University Hospital) included in the study are summarized in Table 1.
      Table 1Demographic characteristics and data on labor and delivery for 138 women included in study and comparison of findings in women who underwent operative vs spontaneous vaginal delivery
      Population characteristicsTotal population

      n = 138
      Operative delivery

      n = 46
      Spontaneous delivery

      n = 92
      P value
      Student t test for continuous data and Fisher exact test for categorical data
      Gestational age, wk39.1 ± 1.539.2 ± 1.639.1 ± 1.4.90
      Maternal age, y27.7 ± 6.629.7 ± 6.526.6 ± 6.4.009
      Body mass index, kg/m229.8 ± 5.332.2 ± 5.828.5 ± 4.7<.001
      Indication for induction of labor
       Postdates61 (44.2)16 (34.8)45 (48.9).15
       Prelabor rupture of membranes32 (23.2)12 (26.0)20 (21.7).67
       Diabetes mellitus17 (12.3)9 (19.6)8 (8.7).10
       Oligohydramnios and/or SGA fetus17 (12.3)5 (10.9)12 (13.0).79
       Hypertensive disease in pregnancy7 (5.1)3 (6.5)4 (4.3).69
       Other4 (2.9)1 (2.2)3 (3.3)1.0
      Method of induction of labor
       Prostaglandins130 (94.2)43 (93.5)87 (94.6)1.0
       Oxytocin8 (5.8)3 (6.5)5 (5.4)1.0
      Bishop score3.9 ± 1.73.1 ± 1.64.3 ± 1.7<.001
      Epidural analgesia29 (21.0)11 (23.9)18 (19.5).35
      Induction to delivery interval, min1510 ± 7201754 ± 8601387 ± 608.004
      Duration of second stage, min
      101 Women.
      76 ± 60141 ± 8870 ± 57.001
      Duration of active second stage, min
      101 Women.
      34 ± 3094 ± 7128 ± 13<.001
      Birthweight, g3251 ± 3873368 ± 3753193 ± 381.012
      Anteroposterior diameter of levator hiatus, mm
       At rest54.6 ± 8.556.1 ± 9.153.8 ± 8.1.13
       At Valsalva59.9 ± 10.460.2 ± 10.959.8 ± 10.3.80
      Levator ani muscle coactivation25 (18.1)10 (21.7)15 (16.3).49
      Data are given as mean ± SD or n (%) unless otherwise noted.
      SGA, small for gestational age.
      Kamel et al. Levator ani contraction and active second stage. Am J Obstet Gynecol 2019.
      a Student t test for continuous data and Fisher exact test for categorical data
      b 101 Women.
      Delivery was spontaneous vaginal in 92 (66.7%), by vacuum in 6 (4.4%), and cesarean in 40 (28.9%) women. Women in the operative delivery group, in comparison with the spontaneous vaginal delivery group, were older, had a higher BMI, and had a higher birthweight, but there were no significant differences between the 2 groups in the anteroposterior diameter of the levator hiatus at rest and at maximum Valsalva, nor in the prevalence of levator ani muscle coactivation.
      In 25 (18.1%) women there was levator ani muscle coactivation and in this group, compared to those without coactivation, there was no significant difference in median gestational age at induction of labor, maternal age, BMI, anteroposterior diameter of the levator hiatus at rest, induction to delivery interval, duration of the second stage, or incidence of epidural anesthesia (Table 2). However, in the levator ani muscle coactivation group the anteroposterior diameter of the levator hiatus at Valsalva was shorter and the duration of the active second stage was longer. There was a significant negative association between the anteroposterior diameter of the levator hiatus at Valsalva and duration of the second stage (r = –0.230; P = .021) and duration of the active second stage (r = –0.338; P = .001). There was no significant association between gestational age at induction of labor, BMI, birthweight, or the anteroposterior diameter of the levator hiatus at rest with either the duration of the second stage or duration of the active second stage. Cox regression analysis, adjusted for potential significant confounders (maternal age and epidural analgesia), demonstrated that levator ani muscle coactivation was the only significant and independent predictor of the duration of the active second stage (hazard ratio, 2.085; 95% confidence interval, 1.158–3.752; P = .014) (Figure 5). Kaplan-Meier survival analysis, with censoring of women who underwent operative delivery in the second stage, confirmed a significantly increased duration of the active second stage in women with coactivation in comparison with women who did not have coactivation (P = .007, log rank test).
      Table 2Comparison of demographic characteristics and data on labor and delivery between women with and without levator ani muscle coactivation
      VariableCoactivation

      n = 25
      No coactivation

      n = 113
      P value
      Student t test for continuous data and Fisher exact test for categorical data
      Gestational age at induction, wk39.0 ± 1.539.2 ± 1.5.52
      Maternal age, y30.0 ± 7.027.2 ± 6.4.06
      Body mass index, kg/m229.9 ± 6.529.7 ± 5.1.90
      Epidural analgesia8 (32.0)21 (18.6).17
      Anteroposterior diameter of levator hiatus, mm
       At rest54.5 ± 8.554.7 ± 8.6.93
       At Valsalva50.1 ± 8.062.1 ± 9.7<.001
      Induction to delivery interval, min1368 ± 4561540 ± 764.28
      Duration of second stage, min
      101 Women.
      101 ± 5971 ± 76.07
      Duration of active second stage, min
      101 Women.
      60 ± 5628 ± 16<.001
      Data are given as mean ± SD or n (%) unless otherwise noted.
      Kamel et al. Levator ani contraction and active second stage. Am J Obstet Gynecol 2019.
      a Student t test for continuous data and Fisher exact test for categorical data
      b 101 Women.
      Figure thumbnail gr5
      Figure 5Cumulative incidence of delivery from beginning of active second stage of labor
      Plot of cumulative incidence of delivery from beginning of active second stage of labor, with respect to levator ani coactivation (dashed line) vs no coactivation (solid line) adjusted for epidural analgesia and maternal age.
      Kamel et al. Levator ani contraction and active second stage. Am J Obstet Gynecol 2019.

      Comment

      Principal findings

      This study has demonstrated that: (1) in nulliparous women undergoing induction of labor at term, levator ani muscle coactivation is associated with a longer active second stage; and (2) larger diameters of the levator hiatus under Valsalva maneuver, but not at rest, are associated with shorter second and active second stage of labor.

      Comparison with results of previous studies

      Viscoelastic properties of the distal birth canal have been suggested as a strong contributor to the time a mother needs to push in the second stage to deliver the fetal head.
      • Tracy P.V.
      • Wadhwani S.
      • Triebwasser J.
      • et al.
      On the variation in maternal birth canal in vivo viscoelastic properties and their effect on the predicted length of active second stage and levator ani tears.
      Previous studies used transperineal ultrasound to investigate the relation between antenatally assessed pelvic organ mobility on Valsalva and levator ani hiatal dimensions in the prediction of outcome of labor and reported that reduced mobility and smaller levator ani hiatal dimensions are associated with increased risk of operative delivery.
      • Dietz H.P.
      • Moore K.H.
      • Steensma A.B.
      Antenatal pelvic organ mobility is associated with delivery mode.
      • Dietz H.P.
      • Lanzarone V.
      • Simpson J.M.
      Predicting operative delivery.
      • Siafarikas F.
      • Staer-Jensen J.
      • Hilde G.
      • Bo K.
      • Ellstrom Engh M.
      Levator hiatus dimensions in late pregnancy and the process of labor: a 3- and 4-dimensional transperineal ultrasound study.
      However, other authors did not find any association between pelvic floor dimensions and the mode of delivery.
      • Lanzarone V.
      • Dietz H.P.
      Three-dimensional ultrasound imaging of the levator hiatus in late pregnancy and associations with delivery outcomes.
      None of these studies evaluated the association between levator ani coactivation and labor outcome. In the present study, we have demonstrated that pelvic hiatal diameter at rest and under Valsalva was not associated with the mode of delivery. However, we have found that pelvic floor relaxation, as represented by larger levator hiatal diameter under Valsalva, was associated with a shorter duration of the second and active second stage of labor.

      Clinical implications

      Many studies have found an association between a prolonged second stage and various adverse labor outcomes. These include increased maternal morbidity, operative delivery rates, complicated cesarean deliveries, chorioamnionitis, severe perineal lacerations, pelvic floor damage, and neonatal complications such as sepsis and asphyxia.
      • Laughon S.K.
      • Berghella V.
      • Reddy U.M.
      • Sundaram R.
      • Lu Z.
      • Hoffman M.K.
      Neonatal and maternal outcomes with prolonged second stage of labor.
      • Sung J.F.
      • Daniels K.I.
      • Brodzinsky L.
      • El-Sayed Y.Y.
      • Caughey A.B.
      • Lyell D.J.
      Cesarean delivery outcomes after a prolonged second stage of labor.
      • Cheng Y.W.
      • Hopkins L.M.
      • Caughey A.B.
      How long is too long: does a prolonged second stage of labor in nulliparous women affect maternal and neonatal outcomes?.
      Our study allows the identification of a group of nulliparous women at risk of a longer second stage of labor prior to induction of labor. Despite the importance of this finding, in the absence of a valid corrective intervention for these women with levator ani muscle coactivation, the clinical applicability of this information remains limited.

      Research implications

      In the present study, we identified a new mechanism involved in the duration of the active second stage of labor, namely levator ani muscle contraction during Valsalva (coactivation) in nulliparous women undergoing induction of labor.
      Conflicting results have been reported on the efficacy of prenatal training of the pelvic floor in improving delivery outcome. A randomized controlled trial in 100 nulliparous women found that antenatal education utilizing observation of the perineum and vaginal examination did not result in altered obstetric outcomes.
      • Phipps H.
      • Charlton S.
      • Dietz H.P.
      Can antenatal education influence how women push in labor?.
      In contrast, another trial in 301 nulliparous women reported that structured pelvic floor training was associated with a lower rate of prolonged second stage labor.
      • Salvesen K.A.
      • Morkved S.
      Randomized controlled trial of pelvic floor muscle training during pregnancy.
      However, both of these studies included an unselected group of nulliparous women and, as shown in our study, >80% of nulliparous women are able to appropriately relax their levator ani muscle during Valsalva. Consequently, future intervention studies should focus in women with levator ani muscle coactivation, who are at increased risk of prolonged active second stage, rather than unselected nulliparous women. Such interventions may include ultrasound coaching by visual feedback which has been reported to be beneficial when used in the labor ward.
      • Gilboa Y.
      • Frenkel T.I.
      • Schlesinger Y.
      • et al.
      Visual biofeedback using transperineal ultrasound in second stage of labor.
      • Bellussi F.
      • Alcamisi L.
      • Guizzardi G.
      • Parma D.
      • Pilu G.
      Traditionally vs sonographically coached pushing in second stage of labor: a pilot randomized controlled trial.

      Strengths and weaknesses

      This is the first study to investigate levator ani muscle coactivation during Valsalva maneuver and the duration of the active second stage of labor in women undergoing induction of labor. Induction of labor is one of the most common obstetrical procedures.
      • Martin J.A.
      • Hamilton B.E.
      • Osterman M.J.
      • Curtin S.C.
      • Matthews T.J.
      Births: final data for 2013.
      • Grobman W.A.
      • Bailit J.
      • Lai Y.
      • et al.
      Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Defining failed induction of labor.
      • Kawakita T.
      • Iqbal S.N.
      • Huang C.C.
      • Reddy U.M.
      Nonmedically indicated induction in morbidly obese women is not associated with an increased risk of cesarean delivery.
      Many predictors of the outcome of induction of labor have been assessed.
      • Kawakita T.
      • Iqbal S.N.
      • Huang C.C.
      • Reddy U.M.
      Nonmedically indicated induction in morbidly obese women is not associated with an increased risk of cesarean delivery.
      • Levine L.D.
      • Downes K.L.
      • Parry S.
      • Elovitz M.A.
      • Sammel M.D.
      • Srinivas S.K.
      A validated calculator to estimate risk of cesarean after an induction of labor with an unfavorable cervix.
      • Rouzi A.A.
      • Alsahly N.
      • Alamoudi R.
      • et al.
      Randomized clinical trial between hourly titrated and 2 hourly static oral misoprostol solution for induction of labor.
      • Connolly K.A.
      • Kohari K.S.
      • Rekawek P.
      • et al.
      A randomized trial of Foley balloon induction of labor trial in nulliparas (FIAT-N).
      • Bauer A.M.
      • Lappen J.R.
      • Gecsi K.S.
      • Hackney D.N.
      Cervical ripening balloon with and without oxytocin in multiparas: a randomized controlled trial.
      • Sagi-Dain L.
      • Sagi S.
      Vaginal delivery within 24 hours of labor induction as a primary outcome—what's the rush?.
      However, the production of a reliable and validated predictive model remains challenging.
      • Reis F.M.
      • Gervasi M.T.
      • Florio P.
      • et al.
      Prediction of successful induction of labor at term: role of clinical history, digital examination, ultrasound assessment of the cervix, and fetal fibronectin assay.
      • Rane S.M.
      • Guirgis R.R.
      • Higgins B.
      • Nicolaides K.H.
      The value of ultrasound in the prediction of successful induction of labor.
      • Hatfield A.S.
      • Sanchez-Ramos L.
      • Kaunitz A.M.
      Sonographic cervical assessment to predict the success of labor induction: a systematic review with metaanalysis.
      • Eggebo T.M.
      • Heien C.
      • Okland I.
      • Gjessing L.K.
      • Romundstad P.
      • Salvesen K.A.
      Ultrasound assessment of fetal head-perineum distance before induction of labor.
      • Pereira S.
      • Frick A.P.
      • Poon L.C.
      • Zamprakou A.
      • Nicolaides K.H.
      Successful induction of labor: prediction by preinduction cervical length, angle of progression and cervical elastography.
      • Gillor M.
      • Vaisbuch E.
      • Zaks S.
      • Barak O.
      • Hagay Z.
      • Levy R.
      Transperineal sonographic assessment of angle of progression as a predictor of successful vaginal delivery following induction of labor.
      • Alavifard S.
      • Meier K.
      • D'Souza R.
      Prediction calculator for induction of labor: no Holy Grail yet!.
      A limitation of the study is that it was restricted to the measurement of the anteroposterior diameter of the levator hiatus. Although other measurements like the levator hiatal area and the transverse diameter may have been interesting to assess, these need 3-dimensional ultrasound machines and skills, which are less readily available and require more operator skills. Another limitation is the inclusion of a heterogeneous group of indications for induction of labor. Since the absolute number of each indication was relatively small, it was not possible in the present study to stratify the results by indication. This can be the subject of a future larger study.

      Conclusion

      In summary, inadequate pelvic floor muscle relaxation as documented by levator ani muscle coactivation in nulliparous women undergoing induction of labor is associated with a longer active second stage of labor. Further studies are needed to investigate the efficacy of antenatal and intrapartum interventions to correct this phenomenon and to assess their potential benefit on labor outcomes.

      Supplementary Data

      References

      1. National Institute for Health and Care Excellence. Intrapartum care for healthy women and babies, 2014. Clinical guideline [CG190]. Available at: https://www.nice.org.uk/guidance/cg190. Accessed September 20, 2018.

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