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National Center for Fetal Medicine, Trondheim University Hospital (St Olav's Hospital) and Department of Laboratory Medicine, Children's and Women's Health, Norwegian University of Science and Technology, Trondheim, Norway
Department of Laboratory Medicine, Children's and Women's Health, Norwegian University of Science and Technology, Trondheim, Norway, and Lund University, Lund, Sweden
National Center for Fetal Medicine, Trondheim University Hospital (St Olav's Hospital) and Department of Laboratory Medicine, Children's and Women's Health, Norwegian University of Science and Technology, Trondheim, Norway
Safe management of the second stage of labor is of great importance. Unnecessary interventions should be avoided and correct timing of interventions should be focused. Ultrasound assessment of fetal position and station has a potential to improve the precision in diagnosing and managing prolonged or arrested labors. The decision to perform vacuum delivery is traditionally based on subjective assessment by digital vaginal examination and clinical expertise and there is currently no method of objectively quantifying the likelihood of successful delivery. Prolonged attempts at vacuum delivery are associated with neonatal morbidity and maternal trauma, especially so if the procedure is unsuccessful and a cesarean is performed.
Objective
The aim of the study was to assess if ultrasound measurements of fetal position and station can predict duration of vacuum extractions, mode of delivery, and fetal outcome in nulliparous women with prolonged second stage of labor.
Study Design
We performed a prospective cohort study in nulliparous women at term with prolonged second stage of labor in 7 European maternity units from 2013 through 2016. Fetal head position and station were determined using transabdominal and transperineal ultrasound, respectively. Our preliminary clinical experience assessing head-perineum distance prior to vacuum delivery suggested that we should set 25 mm for the power calculation, a level corresponding roughly to +2 below the ischial spines. The main outcome was duration of vacuum extraction in relation to ultrasound measured head-perineum distance with a predefined cut-off of 25 mm, and 220 women were needed to discriminate between groups using a hazard ratio of 1.5 with 80% power and alpha 5%. Secondary outcomes were delivery mode and umbilical artery cord blood samples after birth. The time interval was evaluated using survival analyses, and the outcomes of delivery were evaluated using receiver operating characteristic curves and descriptive statistics. Results were analyzed according to intention to treat.
Results
The study population comprised 222 women. The duration of vacuum extraction was shorter in women with head-perineum distance ≤25 mm (log rank test <0.01). The estimated median duration in women with head-perineum distance ≤25 mm was 6.0 (95% confidence interval, 5.2–6.8) minutes vs 8.0 (95% confidence interval, 7.1–8.9) minutes in women with head-perineum distance >25 mm. The head-perineum distance was associated with spontaneous delivery with area under the curve 83% (95% confidence interval, 77–89%) and associated with cesarean with area under the curve 83% (95% confidence interval, 74–92%). In women with head-perineum distance ≤35 mm, 7/181 (3.9%) were delivered by cesarean vs 9/41 (22.0%) in women with head-perineum distance >35 mm (P <.01). Ultrasound-assessed position was occiput anterior in 73%. Only 3/138 (2.2%) fetuses in occiput anterior position and head-perineum distance ≤35 mm vs 6/17 (35.3%) with nonocciput anterior position and head-perineum distance >35 mm were delivered by cesarean. Umbilical cord arterial pH <7.10 occurred in 2/144 (1.4%) women with head-perineum distance ≤35 mm compared to 8/40 (20.0%) with head-perineum distance >35 mm (P < .01).
Conclusion
Ultrasound has the potential to predict labor outcome in women with prolonged second stage of labor. The information obtained could guide whether vacuum delivery should be attempted or if cesarean is preferable, whether senior staff should be in attendance, and if the vacuum attempt should be performed in the operating theater.
Click Video under article title in Contents at ajog.org
Introduction
The tension between optimizing neonatal outcome while promoting vaginal delivery is nowhere more pertinent than in the management of the second stage of labor. Prolonging the upper limit of what is acceptable for duration of the second stage of labor is found to reduce the frequency of cesarean delivery in nulliparous women.
While a higher likelihood of vaginal delivery represents a beneficial maternal outcome, this may not be without risk for the fetus and hence led to concerns from obstetricians.
Furthermore, equating vaginal delivery with optimal outcome is simplistic, as complicated vaginal deliveries are associated to damage to the pelvic floor and anal sphincter ruptures.
So, the goal of obstetric care in the second stage of labor must be to avoid cesarean deliveries where assisted or spontaneous vaginal delivery is likely to be safe and achievable. Unnecessary cesarean delivery has a cumulative effect as it is widely accepted that prevention of the primary cesarean delivery will have an important influence on subsequent deliveries.
The determinants to achieve successful delivery and avoid fetal and maternal complications rely on both accurate assessments of fetal position and station, and on operator skill.
A consensus of current guidance is that operative vaginal delivery is not recommended above station 0 in relation to the ischial spines and that the duration of an operative vaginal delivery should not exceed 20 minutes.
Obstetrics, however, remains a largely subjective art. In clinical obstetrics the fetal head is considered engaged in the mother’s pelvis when the leading part has reached the level of maternal ischial spine (station 0) based on digital examination.
Birth simulator: reliability of transvaginal assessment of fetal head station as defined by the American College of Obstetricians and Gynecologists classification.
Instrumental delivery and ultrasound: a multicenter randomized controlled trial of ultrasound assessment of the fetal head position versus standard care as an approach to prevent morbidity at instrumental delivery.
The ischial spines cannot be seen on ultrasound, but station 0 was found to broadly correspond with head-perineum distance around 35 mm and angle of progression around 120 degrees.
Relationship between fetal head station established using an open magnetic resonance imaging scanner and the angle of progression determined by transperineal ultrasound.
Instrumental delivery and ultrasound: a multicenter randomized controlled trial of ultrasound assessment of the fetal head position versus standard care as an approach to prevent morbidity at instrumental delivery.
The aim of this study was to assess if ultrasound measurements of fetal position and station can predict duration of vacuum extractions, mode of delivery, and fetal outcome in nulliparous women with prolonged second stage of labor.
Materials and Methods
We conducted a prospective cohort study in nulliparous women with prolonged second stage of labor. Eligible for inclusion were those with a live singleton fetus in cephalic presentation and gestational age ≥37 weeks and <42 weeks. The second stage of labor was differentiated into a passive phase (<2 hours) and an active phase with pushing. Women were included and examined with ultrasound when the birth attendant diagnosed prolonged second stage of labor after at least 45 minutes of active pushing and vacuum extraction was considered. Repeated ultrasound examinations were not performed. Women were not eligible when fetal compromise was suspected due to abnormal or nonreassuring cardiotocography.
From November 2013 through July 2016, 223 women were recruited at Stavanger University Hospital, Norway (n = 135); University Hospital of Bologna, Italy (n = 34); Trondheim University Hospital, Norway (n = 16); Queen Charlotte’s and Chelsea Hospital, Imperial College Healthcare National Health Service Trust, London, United Kingdom (n = 14); Lund University Hospital, Sweden (n = 9); Hvidovre University Hospital, Copenhagen, Denmark (n = 9); and University Hospital of Parma, Italy (n = 6). All participating centers had experience in transperineal scanning, and the ultrasound examiners were trained before the start of the study. The ethics committees approved the study with reference numbers Regional Ethics Committee 2012/1865 in Norway; 3348/2013 in Italy; Research Ethics Committee 15/LO/1341, ID project identification 169478 in the United Kingdom; Diarie Number 2012/808 in Sweden; and H-4-2014-038 in Denmark. All women gave informed written consent and the study was registered in Clinical Trials with identifier NCT01878591.
First a transabdominal scan was performed. Fetal head position was defined using a transabdominal or transperineal scan and categorized into occiput anterior (OA) position (Figure 1 and video clip 1) or non-OA position (posterior or transverse position) (Figures 2 and 3 and video clips 2 to 4). The position was described as a clock face with 12 hourly divisions; positions ≥10 o’clock and ≤2 o’clock were classified as OA.
Fetal station was assessed from the transperineal scan. The woman was placed in a semirecumbent position with the legs flexed at the hips and knees at 45-degree and 90-degree angles, respectively, and a transperineal scan performed after ensuring the bladder was empty (Figure 4). Angle of progression was measured in the sagittal plane as the angle between the longitudinal axis of the pubic bone and a line joining the lowest edge of the pubis to the lowest convexity of the fetal skull (Figure 5 and video clip 5).
Head-perineum distance was measured in a transverse transperineal scan (in the axial plane) as the shortest distance from the outer bony limit of the fetal skull to perineum (Figure 6 and video clips 6 and 7). The transducer was placed between the labia majora (in the posterior fourchette), and the soft tissue compressed with firm pressure against the pubic bone without creating discomfort for the woman.
The transducer was angled until the skull contour was as clear as possible, indicating that the ultrasound beam was perpendicular to the fetal skull. A cineloop was stored and used to identify the shortest distance possible between the transducer (perineum) and the fetal skull. This distance represents the remaining part of the birth canal for the fetus to pass. The transperineal measurements were done between contractions, and all ultrasound measurements were done online 2-dimensionally in the labor room. Neither the women nor the birth attendant were informed about the ultrasound results. The ultrasound operator was not involved in clinical decisions or management of labor. Both obstetricians and midwives performed ultrasound examinations.
Woman is placed in semirecumbent position with legs flexed at hips and knees at 45-degree and 90-degree angles, respectively. Transducer placed transverse in posterior fourchette (red line) when head-perineum distance measured and rotated to sagittal plane when angle of progression measured.
Kahrs et al. Sonographic prediction of vacuum deliveries. Am J Obstet Gynecol 2017.
Transverse transperineal image (frontal plane related to woman) illustrating measurement of head-perineum distance (double arrow). Head midline and molding are seen.
Kahrs et al. Sonographic prediction of vacuum deliveries. Am J Obstet Gynecol 2017.
The ultrasound devices used were GE Voluson i (GE Medical Systems, Zipf, Austria) or GE Voluson S6 in Stavanger (GE Medical Systems), Norway, and GE Voluson i in Trondheim, Norway; Lund, Sweden; Copenhagen, Denmark; and Bologna, Italy (GE Medical Systems). In London, United Kingdom, Samsung PT60A and Samsung HM70 were used, and in Parma, Italy, a Samsung WS70 was used (Samsung, Seoul, Republic of Korea). The Malmstrom vacuum cup was the preferred device used in Stavanger and Trondheim, Norway; Lund, Sweden; London, United Kingdom; and Copenhagen, Denmark. In Bologna and Parma, Italy, the Kiwi cup was used. Body mass index was calculated from maternal height and prepregnant weight.
Cord blood was obtained by direct puncture of the umbilical artery without clamping of the cord, and acid-base analysis was performed immediately after collecting the samples. Umbilical artery pH <7.10, known to be associated with adverse neonatal outcome, was used as the cut-off level.
The main outcome measure was duration of vacuum extractions. Secondary outcomes were frequencies of spontaneous deliveries, vacuum extractions, cesarean deliveries, and umbilical artery blood samples after birth (pH and base excess).
Power analysis
Our preliminary clinical experience assessing head-perineum distance prior to vacuum delivery suggested that we should set 25 mm for the power calculation, a level corresponding approximately to +2 below the ischial spines. The main outcome of the study was duration of vacuum extraction analyzed using survival analyses. The main predictor variable was head-perineum distance with a predefined cut-off at 25 mm to discriminate between the groups. To identify a hazard ratio (HR) as low as 1.5 with 80% power, 2-sided test, with alpha 5%, one third of the women with distance >25 mm and two thirds with distance ≤25 mm, we determined that 220 women should be included when expecting 10% censoring. The calculations were based on log rank test using the Freedman method and performed in a statistical program (Stata for Windows, Version 12; StataCorp, College Station, TX).
Statistical analyses
Variables were compared using χ2 test and linear regression. To evaluate differences in the time interval from start of vacuum extraction to complete delivery according to head-perineum distance and angle of progression, we used Kaplan-Meier methods and Cox
regression analyses. The Kaplan-Meier method was used to generate survival plots, and we used head-perineum distance 25 mm as cut-off value in accordance with the power analysis. Cox regression was used to calculate HR as an estimate for relative risk of delivery. In the Cox regression analysis we controlled for fetal position, prepregnancy body mass index, maternal age, induction of labor, epidural analgesia, and augmentation with oxytocin, and in an additional analysis we included institution as a covariate. Women with a spontaneous vaginal delivery were not included in the survival analyses and cesarean deliveries were right censored at the time of the decision to perform a cesarean delivery. Cox regression assumes proportional hazards, and this was evaluated by log minus log plots and tests of Schoenfeld residuals using the global and detailed ph test in Stata software. The assumption was satisfied (P = .66).
The association between head-perineum distance and delivery mode was analyzed at 5 different cut-off levels: ≤20, 21-25, 26-30, 31-35, >35. In a previous study 35 mm was found to correspond to station <0 by clinical examinations,
therefore, we focused on 35 mm as cut-off level and presented test characteristics related to this level. The association between angle of progression and delivery mode was analyzed at cut-off levels: <120, 120-129, 130-139, 140-149, ≥150 degrees. The associations between spontaneous and cesarean delivery related to head-perineum distance and angle of progression as continuous variables were evaluated using receiver operating characteristic (ROC) curves. These analyses were first performed as intention to treat because cesarean deliveries done without a vacuum attempt were included. Thereafter, we did separate analyses that only included cesarean deliveries performed after a vacuum attempt. The area under the curve was considered to have discriminatory potential if the lower limit of the confidence interval (CI) was >0.5. P < .05 was considered statistically significant.
Data were analyzed with the statistical software package SPSS Statistics, Version 23.0 (IBM Corp, Armonk, NY) and Stata for Windows, Version IC 13.
Results
Study population
A total of 223 women were included and 1 woman was excluded because information about the main outcome was missing, leaving 222 women in the study population. Figure 7 is a flow chart illustrating delivery methods. Head-perineum distance was successfully measured in all women and angle of progression was successfully measured in 182/222 (82%). Characteristics of the study population differentiated between women with head-perineum distance ≤25 mm vs >25 mm are presented in Table 1.
Survival analyses were performed in women with a vacuum attempt. The duration of operative delivery was significantly shorter in women with head-perineum distance ≤25 mm (log rank test <0.01) (Figure 8). The estimated median duration (Kaplan-Meier analyses) in women with head-perineum distance ≤25 mm was 6.0 (95% CI, 5.2–6.8) minutes vs 8.0 (95% CI, 7.1–8.9) minutes in women with head-perineum distance >25 mm. The HR in Cox regression analyses was 0.56 (95% CI, 0.41–0.78) and adjusted value 0.58 (95% CI, 0.41–0.82). Head-perineum distance and angle of progression were analyzed as continuous variables in separate analyses. They were both significantly associated with the duration of operative vaginal deliveries after adjusting for covariates. Adjusted HR was 0.96 (95% CI, 0.94–0.98) for increasing head-perineum distance (Table 2) and 0.98 (95% CI, 0.97–0.996) for decreasing angle of progression. The center-adjusted HR estimate for increasing head-perineum distance was 0.93 (95% CI, 0.91–0.96) when the centers were included in the analysis. Duration was >20 minutes in 3 women and 3 women had >2 cup detachments. The median duration from the ultrasound examination to delivery was 25 (interquartile range 15-38) minutes.
Kaplan-Meier plot of time from start of vacuum extraction to delivery within 20 minutes differentiated into those with head-perineum distance ≤25 mm (blue) and >25 mm (green). Women who were delivered by cesarean were censored at time when decision to convert to cesarean was done (P < .01; log rank test).
Kahrs et al. Sonographic prediction of vacuum deliveries. Am J Obstet Gynecol 2017.
Median head-perineum distance in women with fetal head station of 0 from clinical examination was 36 mm, mean 34 mm, range 15-49 mm, and interquartile range 7 mm. Median angle of progression in women with palpated station 0 was 132 degrees, mean 133 degrees, range 112-164 degrees, and interquartile range 24 degrees.
Delivery mode
Head-perineum distance and angle of progression were correlated (r = 0.48). The associations between delivery mode and head-perineum distance and angle of progression were categorized into 5 different groups as presented in Figures 9 and 10. The frequency of cesarean deliveries was 1% (1/99) in women with head perineum distance ≤25 mm vs 12% (15/122) in women with distance >25 mm (P < .01). Using head-perineum distance >35 mm as cut-off level, the sensitivity in predicting cesarean delivery was 56% (95% CI, 33–77%), false-positive rate was 16% (95% CI, 11–21%), positive predictive value was 22% (95% CI, 12–33%), and negative predictive value was 96% (95% CI, 92–98%). Head-perineum distance and angle of progression were significantly associated with a spontaneous delivery with area under the ROC curve 83% (95% CI, 77–89%) (Figure 11) and 75% (95% CI, 66–85%), respectively, but only head-perineum distance was significantly associated with cesarean delivery; area under the ROC curve was 83% (95% CI, 74–92%) for head-perineum distance (Figure 12) vs 56% (95% CI, 42–69%) for angle of progression.
Figure 9Delivery mode related to head-perineum distance
Distribution of spontaneous (green), operative vaginal (blue), and cesarean (red) deliveries in relation to head-perineum distance in nulliparous women with prolonged second stage of labor.
Kahrs et al. Sonographic prediction of vacuum deliveries. Am J Obstet Gynecol 2017.
Distribution of spontaneous (green), operative vaginal (blue), and cesarean (red) deliveries in relation to angle of progression in nulliparous women with prolonged second stage of labor.
Kahrs et al. Sonographic prediction of vacuum deliveries. Am J Obstet Gynecol 2017.
Receiver operating characteristic curves for head-perineum distance in prediction of spontaneous deliveries in women with prolonged second stage of labor.
CI, confidence interval.
Kahrs et al. Sonographic prediction of vacuum deliveries. Am J Obstet Gynecol 2017.
Receiver operating characteristic curves for head-perineum distance in prediction of cesarean deliveries in women with prolonged second stage of labor.
CI, confidence interval.
Kahrs et al. Sonographic prediction of vacuum deliveries. Am J Obstet Gynecol 2017.
We separately analyzed the association of cesarean delivery with head-perineum distance after a vacuum attempt. This occurred in 14/173 (8%) vacuum extractions and the results were similar to the intention-to-treat analyses. Head-perineum distance was associated with a cesarean with 83% (95% CI, 73–93%) vs angle of progression with 52% (95% CI, 38–66%).
Ultrasound-assessed position was OA in 73% and non-OA in 23% with missing information in 4%. In women with head-perineum distance ≤35 mm 7/181 (3.9%) were delivered by cesarean delivery vs 9/41 (22.0%) in women with head-perineum distance >35 mm (P < .01). In fetuses with OA position 6/162 (3.7%) were delivered by cesarean compared to 10/50 (20.0%) in non-OA position (P < .01). Only 3/138 (2.2%) of fetuses in OA position in combination with head-perineum distance ≤35 mm were delivered by cesarean and 6/17 (35.3%) with non-OA position in combination with head-perineum distance >35 mm were delivered by cesarean.
Umbilical artery blood samples
pH in the umbilical artery were measured in 184/222 (83%) cases. Only 1 newborn had pH <7.0 (pH 6.90 and base excess 18). This baby was delivered by vacuum and head-perineum distance before start of vacuum was 38 mm. pH <7.10 occurred in 10 newborns, and head-perineum distance was >35 mm in 8/40 (20.0%) compared to 2/144 (1.4%) in cases with head-perineum distance ≤35 mm (P < .01). Base excess was >12 in 3 cases in which head-perineum distance was >35 mm in 2.
Comment
Principal findings
The main finding in our study was a significant association between ultrasound-assessed fetal station and duration of vacuum extraction. Fetal station assessed with head-perineum distance and angle of progression predicted the probability of a spontaneous delivery, but only head-perineum distance predicted cesarean delivery. We observed significant association between low umbilical cord pH and head-perineum distance >35 mm.
The importance of these findings differs in high and low resource countries. Firstly, the transperineal scan requires little training and can be undertaken with the type of ultrasound equipment frequently found in many delivery units worldwide. Thus, the technique is generalizable. In high-income countries, the benefit of the technique is 3-fold: (1) a previously subjective and unreproducible measurement is converted into an objective and recordable measure; (2) knowledge of the likely difficulty and duration of labor will determine the seniority of the operator and the setting of the delivery; and (3) the likelihood of cesarean delivery can be discussed with the woman and a decision made in advance not to proceed with a potentially futile attempt at vacuum delivery.
In many low- and mid-resource countries there is an increase in cesarean rates and declining use of operative vaginal deliveries, including vacuum.
In low-resource countries cesarean delivery is associated with increased risk of maternal complications and high risk of uterine rupture in subsequent pregnancies.
Cesarean section without medical indications is associated with an increased risk of adverse short-term maternal outcomes: the 2004-2008 WHO Global Survey on Maternal and Perinatal Health.
and use of intrapartum ultrasound might add important information and reassure clinicians that a vacuum attempt at low stations has low risk of failure. New studies in low-resource settings are necessary.
Clinical significance
We found that head-perineum distance ≤20 mm was associated with a high probability of a spontaneous delivery (Figure 9), and birth attendants might be patient in these situations as long as the fetal heart rate is normal. In a previous study head-perineum distance >35 mm corresponded to station ≥0,
and this finding agreed well with our new study (mean head-perineum distance 34 mm and median head-perineum distance 36 mm at clinically assessed station 0). It is usually not recommended to perform an operative vaginal delivery at levels above this station.
We found that the probability of cesarean in women with head-perineum distance >35 mm was 22% and 35% if it was combined with a non-OA position. A failed operative vaginal delivery is associated with risks for the mother and the fetus and a fearful experience for the woman. Our study confirms that vacuum deliveries at high station are associated with a high failure risk, but at head-perineum distance levels <35 mm there is very good chance (96%) of a vaginal delivery. Another important finding is that pH <7.10 was more commonly observed among cases with head-perineum distance >35 mm. Although our study did not include fetuses with suspected compromise before start of vacuum, a significantly lower pH in cases with greater head-perineum distance might be explained by the longer duration of vacuum extractions at higher levels.
Research implications
Labor progress in the second stage of labor is evaluated by fetal descent and traditionally assessed by clinical assessment of station.
suggested angle of progression as a measure of head descent and found that an angle of >120 degrees was associated with subsequent spontaneous vaginal deliveries. Sonographically assessed head station has already been shown to be associated with duration of labor and delivery mode in nulliparous women with prolonged first stage.
Transperineal ultrasound imaging in prolonged second stage of labor with occipitoanterior presenting fetuses: how well does the 'angle of progression' predict the mode of delivery?.
evaluated 41 women with prolonged second stage of labor, but included only the 26 women with OA position in the final analyses. They found that angle of progression >120 degrees was associated with a spontaneous delivery or an easy vacuum extraction.
Transperineal ultrasound imaging in prolonged second stage of labor with occipitoanterior presenting fetuses: how well does the 'angle of progression' predict the mode of delivery?.
studied 20 women and found that head direction with respect to the long axis of the symphysis was associated with a successful operative vaginal delivery. Sainz et al
Utility of intrapartum transperineal ultrasound to predict cases of failure in vacuum extraction attempt and need of cesarean section to complete delivery.
measured angle of progression in 235 women immediately before vacuum extraction. Duration of extraction exceeding 20 minutes or detaching of the vacuum cup >3 times were defined as failed vacuum extraction. The area under the ROC curve for predicting failure of vacuum extraction was 67% (95% CI, 57–77%) with optimal cut-off at 146 degrees. Our results cannot be directly compared with this study because our prespecified outcome was different. We found that head-perineum distance predicted cesarean delivery with area 83% (95% CI, 74–92%) under the ROC curve. It should be noted that in our study the duration of vacuum extraction exceeded 20 minutes in only 3 women, 3 women experienced >2 detachments, and that the frequency of cesarean after a vacuum attempt was 8%. In the original studies angle of progression was only used in OA fetuses. In our study, all positions were included. The third cardinal movement is different in occiput posterior positions
Re: Narrow subpubic arch angle is associated with higher risk of persistent occiput posterior position at delivery. T. Ghi, A. Youssef, F. Martelli, F. Bellussi, E. Aiello, G. Pilu, N. Rizzo, T. Frusca, D. Arduini and G. Rizzo. Ultrasound Obstet Gynecol 2016;48:511-515.
and this might explain why angle of progression did not predict cesarean. Because varying cut-off levels for the angle of progression in predicting cesarean deliveries are suggested in previous studies (from 120-146 degrees),
Transperineal ultrasound imaging in prolonged second stage of labor with occipitoanterior presenting fetuses: how well does the 'angle of progression' predict the mode of delivery?.
we decided to investigate angle of progression as a continuous variable.
Head-perineum distance is easy to measure and can be used at all stations. The transabdominal transducer should be placed in the posterior fourchette and pressed until resistance against the pubic arches is achieved. Repeatability has been investigated in a previous study. The intraobserver variation was within 3 mm in 87%, and the interobserver variation was within 3 mm in 61%. The limits of agreement for intraobserver variation were –3.0 to 5.3 mm, and for interobserver agreement –8.5 to 12.3 mm.
A randomized study is warranted, but it might be difficult to perform because adverse fetal outcomes are fortunately rare. It is shown that women prefer ultrasound examinations before vaginal examination,
Comparison of effects of digital vaginal examination with transperineal ultrasound during labor on pain and anxiety levels: a randomized controlled trial.
and maternal experiences of fear and pain might be used as outcomes in a future randomized study.
Strengths and limitations
Strengths of this study are the multicenter design, inclusion of only nulliparous women with prolonged second stage in the active phase of labor, and that the ultrasound examiners and the birth attendants were blinded to each other’s findings. Limitations of the study were that some centers had few inclusions and that different vacuum devices were used. The study period was long with relatively few inclusions/months because it was often difficult to find ultrasound examiners not involved in the clinical care, and the integrity of the study relied on study examinations not biasing clinical decisions.
In measuring angle of progression, the complete length of the symphysis and the skull contour should be visualized on the same image; this failed in 18% of the cases. Women could be included after 45 minutes of active pushing. In the Norwegian guidelines operative delivery is recommended after 1 hour of active pushing.
This period differs from recommendations in many other countries and might affect the external validity of the study since the majority of participants were Norwegian women. The final decision of delivery method was based on subjective considerations of the responsible physician, and difficult to standardize. The study design was observational, and local guidelines should be followed.
Conclusion
In summary, ultrasound measurement in women with prolonged second stage of labor might predict duration of assisted vaginal delivery and the likelihood of cesarean delivery, and was associated with fetal acid-base status. We did not examine the clinical impact of this information nor did we attempt to change clinical decision-making. This work sets the scene for further studies of management in prolonged second stage of labor.
Acknowledgment
We would like to thank Helen Barton for her work in recruitment for the study, Johanne Kolvik Iversen for recording video clips, and Ingrid Frøysa and Morten Dreier for illustrations. Thanks to the UK National Institute for Health Research Biomedical Research Centre based at Imperial College Healthcare National Health Service Trust and Imperial College London.
Transverse transperineal scanning in early labor. Soft tissue is first compressed; thereafter transducer is angled forward until pubic bones are seen. Head-perineum distance is measured as shortest distance from transducer to outer boarder of fetal skull. Cineloop is helpful in measuring shortest head-perineum distance. Pubic bones should not be seen when head-perineum distance is measured.
Kahrs et al. Sonographic prediction of vacuum deliveries. Am J Obstet Gynecol 2017.
Birth simulator: reliability of transvaginal assessment of fetal head station as defined by the American College of Obstetricians and Gynecologists classification.
Instrumental delivery and ultrasound: a multicenter randomized controlled trial of ultrasound assessment of the fetal head position versus standard care as an approach to prevent morbidity at instrumental delivery.
Relationship between fetal head station established using an open magnetic resonance imaging scanner and the angle of progression determined by transperineal ultrasound.
Cesarean section without medical indications is associated with an increased risk of adverse short-term maternal outcomes: the 2004-2008 WHO Global Survey on Maternal and Perinatal Health.
Transperineal ultrasound imaging in prolonged second stage of labor with occipitoanterior presenting fetuses: how well does the 'angle of progression' predict the mode of delivery?.
Utility of intrapartum transperineal ultrasound to predict cases of failure in vacuum extraction attempt and need of cesarean section to complete delivery.
Re: Narrow subpubic arch angle is associated with higher risk of persistent occiput posterior position at delivery. T. Ghi, A. Youssef, F. Martelli, F. Bellussi, E. Aiello, G. Pilu, N. Rizzo, T. Frusca, D. Arduini and G. Rizzo. Ultrasound Obstet Gynecol 2016;48:511-515.
Comparison of effects of digital vaginal examination with transperineal ultrasound during labor on pain and anxiety levels: a randomized controlled trial.
C.C.L. is supported by the UK National Institute for Health Research Biomedical Research Centre based at Imperial College Healthcare National Health Service Trust and Imperial College London.
The authors report no conflict of interest.
Cite this article as: Kahrs BH, Usman S, Ghi T, et al. Sonographic prediction of outcome of vacuum deliveries: a multicenter, prospective cohort study. Am J Obstet Gynecol 2017;217:69.e1-10.
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