Ultrasound criteria for labor dystocia in the second stage of labor

Objective: to establish ultrasound diagnostic criteria for labor dystocia (uterine inertia) during the second stage of labor.

Materials and Methods. A prospective study was conducted involving 253 patients. The study group consisted of 73 women whose labor was complicated by second-stage labor dystocia. Within this group, oxytocin augmentation was effective in 40 (54.8%) patients, resulting in vaginal delivery; in 11 (15.1%) patients, augmentation was entirely ineffective, and delivery was completed by Cesarean section. In 22 (30.1%) patients diagnosed with labor dystocia, delivery was completed by vacuum extraction; among these, 17 underwent oxytocin augmentation, and 5 were subsequently excluded from the data analysis due to the development of fetal hypoxia. In 5 cases, labor dystocia was recorded when the fetal head was already on the pelvic floor with conditions met for vacuum extraction, leading to the decision to forego oxytocin augmentation. The control group consisted of 180 patients with an uncomplicated second stage of labor. Starting from the onset of the second stage, all patients underwent hourly transperineal ultrasound to determine the angle of progression (AoP) and the delta angle of progression (ΔAoP). The diagnosis of labor dystocia was established clinically using digital vaginal examination based on the classical criteria that the fetal head should normally progress through the birth canal at a rate of one pelvic plane or more per hour.

Results. In uncomplicated labor (“green zone”), the AoP at the beginning of the second stage is ≥120°, and the leading point of the fetal head is located below the interspinal plane, with hourly increases in AoP and ΔAoP being ≥20° and ≥16°, respectively. In cases where the AoP was ≤110° at the beginning of the second stage, labor was complicated by dystocia in all patients, requiring prolonged augmentation; the hourly increase in AoP did not exceed 10° (median 5.6° [0–10°]). The median ΔAoP at the time of labor dystocia diagnosis was 7° [0–10°] ("red zone"), and these parameters differed significantly between the study and control groups (p < 0.01). Thus, objective ultrasound criteria for the development of labor dystocia were defined as: AoP ≤110°, AoP dynamics ≤10°/hour, and ΔAoP ≤10°. A diagnosis of labor dystocia is established when two or more criteria were identified during hourly measurements. If AoP and ΔAoP values fell between the boundaries of the “green” and “red” zones (“yellow zone”), measurements were performed hourly for the following 2 hours; a diagnosis of labor dystocia was made if the values remained within the yellow zone upon repeated assessment.

Conclusion. Dynamic ultrasound during the second stage of labor provides the opportunity for timely diagnosis of labor dystocia based on objective criteria. This approach reduces the number of digital vaginal examinations, thereby decreasing the risk of maternal and fetal infectious complications, improving maternal birth satisfaction, and preventing unnecessary interventions such as unjustified augmentation or operative delivery, which may ultimately improve perinatal outcomes.

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