This study aimed to investigate the diagnostic performance of transperineal ultrasound–measured angles of progression at the onset of the second stage of labor for the prediction of spontaneous vaginal delivery in singleton term pregnancies with cephalic presentation.
We performed a predefined systematic search in PubMed, Embase, Scopus, Web of Science, and Google Scholar from inception to February 5, 2021.
Study Eligibility Criteria
Prospective cohort studies that evaluated the diagnostic performance of transperineal ultrasound–measured angles of progression (index test) at the onset of the second stage of labor (ie, when complete cervical dilation is diagnosed) for the prediction of spontaneous vaginal delivery (reference standard) were eligible for inclusion. Eligible studies were limited to those published as full-text articles in the English language and those that included only parturients with a singleton healthy fetus at term with cephalic presentation.
Study Appraisal and Synthesis Methods
Study quality was assessed using the Quality Assessment of Diagnostic Accuracy Studies 2 tool. Summary receiver operating characteristic curves, pooled sensitivities and specificities, area under the curve, and summary likelihood ratios were calculated using the Stata software. Subgroup analyses were done based on angle of progression ranges of 108° to 119°, 120° to 140°, and 141° to 153°.
A total of 8 studies reporting on 887 pregnancies were included. Summary estimates of the sensitivity and specificity of transperineal ultrasound–measured angle of progression at the onset of the second stage of labor for predicting spontaneous vaginal delivery were 94% (95% confidence interval, 88%–97%) and 47% (95% confidence interval, 18%–78%), respectively, for an angle of progression of 108° to 119°, 81% (95% confidence interval, 70%–89%) and 73% (95% confidence interval, 57%–85%), respectively, for an angle of progression of 120° to 140°, and 66% (95% confidence interval, 56%–74%) and 82% (95% confidence interval, 66%–92%), respectively, for an angle of progression of 141° to 153°. Likelihood ratio syntheses gave overall positive likelihood ratios of 1.8 (95% confidence interval, 1–3.3), 3 (95% confidence interval, 2–4.7), and 3.7 (95% confidence interval, 1.7–8.1) and negative likelihood ratios of 0.13 (95% confidence interval, 0.07–0.22), 0.26 (95% confidence interval, 0.18–0.38), and 0.42 (95% confidence interval, 0.29–0.60) for angle of progression ranges of 108° to 119°, 120° to 140°, and 141° to 153°, respectively.
Angle of progression measured by transperineal ultrasound at the onset of the second stage of labor may predict spontaneous vaginal delivery in singleton, term, cephalic presenting pregnancies and has the potential to be used along with physical examinations and other clinical factors in the management of labor and delivery.
Accurate prediction of successful vaginal delivery in pregnant women could lead to improved neonatal and maternal outcomes by decreasing the rates of prolonged, nonprogressive labors that are converted to cesarean deliveries. It is well known that intrapartum cesarean deliveries are associated with less favorable outcomes than elective cesarean deliveries, especially after failure of a prolonged trial of vaginal delivery.
Why was this study conducted?
This study aimed to systematically investigate the diagnostic performance of the angle of progression, as measured by ultrasound at the onset of the second stage of labor, as a predictor of spontaneous vaginal delivery in term singleton pregnancies with cephalic presentation.
Overall, the ultrasound-measured angle of progression at the onset of the second stage of labor shows moderate diagnostic performance (with a sensitivity of 80%, specificity of 81%, and an area under the curve of 0.87) for predicting spontaneous vaginal delivery. The pooled sensitivity and specificity for narrower angles of progression (108°–119°) were 94% and 47%, respectively, compared with 66% and 82% for wider angles of progression (141°–153°), respectively.
What does this add to what is known?
Angle of progression, as measured at the onset of the second stage of labor at rest, can be used to predict the mode of delivery in singleton term pregnancies and has the potential to be incorporated in models and calculators for the prediction of spontaneous vaginal delivery.
Parameters obtained using abdominal and digital vaginal examinations, both before the onset of labor and during labor, have been evaluated as predictors of spontaneous vaginal delivery. Their accuracy for predicting the delivery mode is, however, variable and not sufficiently robust for clinical use. ,
Ultrasound measurements have been evaluated as possible tools for predicting the success of vaginal delivery. One parameter that can be obtained during the first stage of labor is the angle of progression (AoP). It is acquired using a transperineal ultrasound (TPUS) and involves measuring the angle between the long axis of the symphysis pubis and the line drawn from its lower edge, tangent to the leading skull bone. This angle can be used to predict the rate and likelihood of continued fetal head descent. However, to date, the data on the predictive role of the AoP are heterogenous. Previous studies were conducted during different stages of labor, and some were confounded by the inclusion of AoP values measured before the onset of labor. Given that the AoP is expected to change substantially from the prelabor period to when labor starts and becomes active, , we sought to evaluate this ultrasound parameter only during labor.
The aim of this systematic review and meta-analysis was to systematically examine the diagnostic performance of the AoP, as measured by intrapartum TPUS at the onset of the second stage of labor (once complete cervical dilation is diagnosed) and before pushing efforts began, to predict spontaneous vaginal delivery in singleton, term pregnancies with cephalic presentation.
Methods and Materials
This meta-analysis was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses checklist. The study protocol for this systematic review was registered in the International Prospective Register of Systematic Reviews (registration number CRD42020207288).
Information sources and search strategy
A systematic literature search of PubMed, Web of Science, Google Scholar, Scopus, and Embase from the date of database inception to February 7, 2021, was performed by 2 independent authors (K.H. and A.A.N.). The search was conducted using the following key words: (“angle of progression” OR “angle progression” OR “progression angle” OR “angle of descent” OR “angle descent” OR “descent angle” OR “angle of fetal head progression” OR “angle of head progression” OR “angle of fetal head descent” OR “angle of head descent” OR “head progression angle” OR “head descent angle”) AND (“mode of delivery” OR “cesarean delivery” OR “cesarean section” OR “C-section” OR “vaginal delivery” OR “vaginal birth”) AND (“second stage” OR “2nd stage”). The reference lists of all relevant articles were reviewed by an investigator, and further eligible studies, obtained from references identified within selected articles, were added to the results of the electronic literature search.
Eligibility criteria and study selection
In terms of predicting the mode of delivery, we only included studies reporting on the accuracy of TPUS-measured AoP at the onset of the second stage of labor before pushing. The index test in this meta-analysis was TPUS-measured AoP, and the reference standard we used was the actual route of delivery, namely vaginal delivery vs operative delivery (cesarean delivery or instrumental delivery). Studies were excluded if they (1) were retrospective by design; (2) included noncephalic presentation, multiple gestations, or severe maternal or fetal complications that impacted the labor process; (3) did not provide test accuracy estimates or sufficient information to draw a 2×2 table; and (4) if the AoP was measured during a uterine contraction or during second stage pushing. Furthermore, case reports, case series, conference abstracts, and review articles were excluded. The search was limited to articles published in the English language. Selected studies were reviewed for eligibility by 2 independent authors (K.H. and A.A.N.), and any discrepancies between reviewers were resolved by consulting a third investigator (A.A.S.).
Data extraction and outcome measure
Data abstraction from the included articles was performed by 2 independent authors (A.A.N. and K.H.) using a standardized protocol. The following data were abstracted: first author’s name, publication year, type of study design, number of participants, ultrasound technique, timing of the ultrasound examination, AoP cutoff values, and inclusion and exclusion criteria as defined by the authors of each study. For those studies for which the true positive (TP), false positive (FP), false negative (FN), and true negative (TN) values were not available, we either reconstructed 2×2 tables using sensitivity and specificity as previously described or contacted the corresponding authors (C.B. and V.M.) to get the missing data, especially data related to whether AoP measurements were obtained at rest or during pushing.
The main outcome measure was determination of the pooled sensitivity, specificity, and area under the curve (AUC) of the AoP, measured at the onset of the second stage of labor, to predict spontaneous vaginal delivery. Positive and negative likelihood ratios (LRs) were calculated using the pooled sensitivity and specificity. The subgroup analyses were performed based on whether the outcome of the study was a comparison of vaginal vs cesarean delivery or vaginal vs operative delivery (cesarean delivery or instrumental delivery).
Measurement of the angle of progression
The most common technique used to determine the AoP is to use a TPUS in the sagittal plane and to measure the angle between a line placed through the midline of the pubic symphysis and a line running from the inferior apex of the symphysis pubis tangentially to the fetal skull ( Figure 1 ).
Assessment of risk of bias
The Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) was used to evaluate the quality of the included studies and the risk of bias. QUADAS-2 includes “patient selection,” “index test,” “reference standard,” and “flow and timing” domains to determine the risk of bias and includes “patient selection,” “index test,” and “reference standard” domains to determine applicability concern. Each of the above items was scored as being at high, low, or unclear risk of bias. None of the included studies in this meta-analysis were excluded because of an unclear or high risk of bias.
A random-effects model was used in this meta-analysis. The overall pooled sensitivities, specificities, positive likelihood ratios (LRs+), negative likelihood ratios (LRs−), and diagnostic odds ratios (ORs) with corresponding 95% confidence intervals (CIs) were calculated from the TP, FP, FN, and TN values for each study to indicate the accuracy of the AoP for predicting the delivery mode. The pooling of accuracy measures was performed twice. Only the cutoff values with the highest diagnostic accuracy (demonstrated by the AUC) were used for the pooling of estimate measures.
In addition, a summary receiver operating characteristic (sROC) curve was constructed as described previously. The heterogeneity of the pooled studies was assessed by the inconsistency index (I 2 ). An I 2 value of >50% indicates significant heterogeneity. The following reference values have been suggested for the interpretation of diagnostic AUC values: low (0.5≥AUC≤0.7), moderate (0.7≥AUC≤0.9), or high (0.9≤AUC≥1). Clinical applicability of the TPUS-measured AoP was evaluated by the Fagan nomogram, which was constructed by using the LR+ and LR− values.
All statistical analyses were performed using Stata, version 12.0 (StataCorp LLC, College Station, TX).
Study selection and characteristics
A total of 170 articles were retrieved. Of these, 62 articles were excluded for duplication. The remaining 108 studies were screened for eligibility. Title and abstract screening led to the identification of 83 potentially eligible studies. After full-text assessment was conducted, 8 studies met our inclusion criteria and were included in this review ( Figure 2 ).
All of the studies were prospective and published between 2013 and 2021 and collectively included data on 877 singleton pregnancies that underwent a TPUS at the beginning of the second stage of labor before pushing efforts were started and not during a contraction. All eligible studies used the same technique of TPUS to determine the AoP (described above in Methods and Materials). In all of the included studies, obstetricians responsible for the clinical management of the parturients were blinded to the US findings. Further details on the characteristics of the included studies and their inclusion and exclusion criteria are reported in Table 1 .
|Study, year (country)||Study design||Sample size (spontaneous vs operative delivery)||Ultrasound performed at rest or pushing||Ultrasound technique||Timing of ultrasound examination||Cutoff points||Inclusion and exclusion criteria||TP, FP, FN, TN|
|Ghi et al, 2013 (Italy)||Prospective||71 (58 vs 13)||Rest||Midsagittal TPUS||Second stage of labor||108°||Inclusion: nulliparous women with uncomplicated singleton pregnancies at term gestation with fetuses in cephalic presentation. Exclusion: patients were excluded from the study if they underwent cesarean delivery during the first stage of labor or if cesarean delivery or instrumental vaginal delivery was performed in the second stage purely because of an abnormal fetal heart trace.||58, 8, 0, 5|
|Marsoosi et al, 2015 (Iran)||Prospective||70 (59 vs 11)||Rest a||Midsagittal TPUS||Second stage of labor||113°||Inclusion: term (≥37 wk) viable singleton pregnancy with cephalic presentation. Exclusion: multiple pregnancies, preterm labor, nonocciput anterior fetal head position at the beginning of second stage of labor and cesarean delivery before the second stage of labor.||59, 2, 6, 3|
|Ciaciura-Jarno et al, 2016 (Poland)||Prospective||68 (60 vs 8)||Rest||Midsagittal TPUS||Second stage of labor||126°||Inclusion: term singleton fetuses in cephalic longitudinal presentation. Exclusion: multiple pregnancy; defects of the uterus; condition after uterus surgery; and epidural anesthesia.||51, 0, 9, 8|
|Kameyama et al, 2016 (Japan)||Prospective||50 (42 vs 8)||Rest||Midsagittal TPUS||Second stage of labor||146°||Inclusion: pregnant women at term (37 wk) with a live singleton fetus in cephalic presentation. Exclusion: NR.||33, 2, 9, 6|
|Bibbo et al, 2018 (United States)||Prospective||137 (104 vs 33)||Rest a||Midsagittal TPUS||Second stage of labor||147.5°, 153°||Inclusion: nulliparous, older than 18 y, had a live singleton gestation at term, and were admitted to the labor and delivery unit in spontaneous labor or for labor induction. Exclusion: fetuses were known to have a complex fetal anomaly were not eligible. We defined complex fetal anomaly as any fetus that had multiple severe anomalies that encompassed more than 2 organ systems.||70, 3, 34, 30|
|Carvalho Neto et al, 2019 (Brazil)||Prospective||221 (153 vs 68)||Rest||Midsagittal TPUS||Second stage of labor||129.9°||Inclusion: term live fetus in cephalic presentation. Exclusion: patients admitted for emergency situations requiring immediate resolution of the pregnancy by cesarean delivery, such as uterine rupture, umbilical cord prolapse, premature placental abruption, and cardiac tracings classified as category 3 were excluded.||96, 10, 57, 58|
|Hadad et al, 2020 (Israel)||Prospective||197 (166 vs 31)||Both b||Midsagittal TPUS||Second stage of labor||138°, 126°, 116°||Inclusion: nulliparous; term and singleton pregnancy; with neuraxial analgesia. Exclusion: women were excluded from the study if their operative delivery was due solely to nonreassuring fetal heart rate.||120, 5, 46, 26|
|Brunelli et al, 2021 (Italy)||Prospective||63 (46 vs 17)||Rest||Midsagittal TPUS||Second stage of labor||118.5°||Inclusion: singleton pregnancy and fetuses in cephalic presentation at term of gestation (37–41 wk). Exclusion: we excluded women with previous uterine surgery, suspected fetal asphyxia, major fetal malformations, occiput anterior and transverse at transabdominal scan performed at the beginning of the second stage of labor.||40, 3, 6, 14|