Sonographic evaluation in the second stage of labor to improve the assessment of labor progress and its outcome

Every pregnant woman in early spontaneous labor or admitted for induction of labor wishes to know if she will deliver vaginally, or if she will require an operative delivery. Will the energy, pain, and the effect of labor on the pelvic floor be worth a vaginal delivery? What are the consequences of a failed attempt at a vaginal delivery? It would be ideal if, before the onset of labor or in its early phases, we could accurately predict who will deliver vaginally spontaneously without complications, and who will require an operative delivery (abdominal or assisted). This information would reduce morbidity, improve safety, optimize utilization of resources, and improve satisfaction of women with the labor and/or delivery process. The results of a prospective observational study of 202 nulliparous women suggested that the mode of delivery could be predicted accurately in up to 87% of cases before the onset of labor, with a combination of clinical and historical factors as well as ultrasound findings.1 Sonographic examination has the potential to improve the predictive accuracy – such an improvement is highly desirable. The partogram was the crucial advance which allowed an objective mean to assess labor progress by plotting cervical dilatation and station as a function of time.2–15 (Figure 1) Before partograms, evaluation of labor progress was subjective and often monitored according to its duration. With the development of the partogram, in the middle part of the twentieth century, labor disorders were defined and classified (prolonged latent phase, protracted, and arrest disorders). The pelvic division of labor, which encompasses the phase of parturition during which the fetus descends through the birth canal, is defined by changes in station of the presenting part.16 It is noteworthy that descent begins before full dilation (Figure 1). The management of protracted descent (nulliparous: 1cm/hour or less; multiparous: 2cm/hour or less), arrest of descent (no change in station for 1 hour or more), or failure to descend (no change in the deceleration phase or the second stage)13 remain one of the most challenging problems of obstetrics. Indeed, the skill and judgment required to decide when and how to intervene have been defining factors of the art of obstetrics. Figure 1 Partogram developed by Emanuel Friedman which describes the relationship between time in the horizontal axis and two variables: cervical dilatation and station of the presenting part. Reproduced from: Friedman EA. Dysfunctional labor. In Management of ... Operative vaginal deliveries were introduced as a heroic measure to deal with obstructed labor. The feasibility of an abdominal delivery, its improved technique and safety, coupled with a concern for fetal and neonatal welfare have changed the components of the obstetrical equation to opt for a particular mode of delivery (vaginal operative delivery versus abdominal). Ultrasound has earned its role in obstetrics through the assessment of gestational age, fetal growth, detection of congenital anomalies, fetal well-being and cervical length. In this Editorial, we reaffirm the notion that ultrasound is superior to digital vaginal examinations in determining fetal position prior to operative delivery,17–26 and explore the concept that sonography brings objectivity in assessing the location of the presenting part (station), and may contribute substantially to the clinical management of the second stage of labor. This issue of the “Journal” contains several original contributions which support this view. A pioneering study by Antonio Barbera et al.27 (from Professor John Hobbins' group) reports the use of transperineal/translabial ultrasound,28 and describes that the angle between the symphysis pubis and the leading part of the fetal skull (“angle of progression”) can predict which patient would deliver vaginally and which one would be at risk for requiring an abdominal delivery. The concept was originally described in a DVD in 2003 (under the sponsorship of the American College of Obstetricians and Gynecologists).29 The study is now published in this issue of the Journal.27 An angle of progression of 120 degrees or more (Figure 2) was associated in all cases with a spontaneous vaginal delivery. The angle was also associated with the duration of the examination-to-delivery interval. The intra-observer and inter-observer variability of the angle of progression were low, and there was a good correlation between clinical assessment of progress and the angle of progression. Figure 2 “Angle of progression”. This is the angle formed between a line placed through the midline of the symphysis pubis, and a second line (in red) drawn from the inferior apex of the symphysis tangentially to the fetal skull. In this figure, ... This concept has been independently studied by Professor Karim Kalache at the Charite University Hospital in Berlin, in the Department of Professor Joachim Dudenhausen.30 Among 26 cases with an occiput anterior fetal position, an angle of progression of 120 degrees or more was associated with a probability of successful vaginal delivery of 90% (derived from logistic regression). Collectively, the evidence suggests that the simple determination of the angle of progression has important prognostic value. Since engagement of the fetal head is a major prognostic factor for the outcome of labor,31–33 and its diagnosis by clinical means has many shortcomings, ultrasound has been used to improve the accuracy of its diagnosis. “Engagement” is said to have occurred when the widest diameter of the fetal presenting part has passed beyond the plane of the maternal pelvic inlet.34 In a cephalic presentation, the head usually is engaged when the leading part of the skull is at or below the level of the maternal ischial spines. The diagnosis of engagement can be made clinically by transvaginal digital examination, or transabdominal examination (using the fourth Leopold maneuver and finding that two-fifths of the fetal head is palpable).35