Can ultrasound on admission in active labor predict labor duration and a spontaneous delivery?

Abstract

Background Identifying predictive factors for a normal outcome at admission in the labor ward would be of value for planning labor care, timing interventions and in preventing labor dystocia. Clinical assessments of fetal head station and position at the start of labor have some predictive value but the value of ultrasound methods for this purpose has not been investigated. Studies using transperineal ultrasound before labor onset show possibilities of using these methods to predict outcome. Objective To investigate if ultrasound measurements during the first examination in the active phase of labor were associated with the duration of labor phases and the need for operative delivery. Study Design This was a secondary analysis of a prospective cohort study at Landspitali University Hospital, Reykjavik, Iceland. Nulliparous women at ≥37 weeks with a single fetus in cephalic presentation and spontaneous labor onset were eligible. The recruitment period was from January 2016 to April 2018. Women were examined by a midwife on admission and included if in established active phase defined as regular contractions with a fully effaced cervix, open four cm or more. An ultrasound examination was performed by a separate examiner within 15 minutes, both examiners were blinded to the other's results. Transabdominal and transperineal ultrasound were used to assess fetal head position, cervical dilatation and fetal head station expressed as head-perineum distance and angle of progression. Duration of labor was estimated as the hazard ratio for spontaneous delivery using Kaplan-Meier curves and Cox regression analysis. The hazard ratios were adjusted for maternal age and BMI. The associations between study parameters and mode of delivery were evaluated using receiver-operating characteristic curves. Results Median time to spontaneous delivery when head-perineum distance was ≤45 mm was 490 minutes compared to 682 min when >45mm (log rank test, p=0.009, but the adjusted HR for shorter HPD was 1.47; 95% CI; 0.83 to 2.60). For angle of progression ≥93° the median duration was 506 minutes compared to 732 min when <93° (log rank test, p=0.008, adjusted HR for AoP was 2.07; 95% CI: 1.15 to 3.72). The median time to delivery for non-occiput posterior positions was 506 minutes compared with 677 minutes for occiput posterior positions (log rank test, p=0.07, adjusted HR 1.52; 95% CI: 0.96- 2.38) Median time to delivery was 429 minutes for dilatation of ≥6 cm and 704 minutes for dilatation of 4-5 cm (log rank test, p=0.002, adjusted HR 3.11; 95% CI: 1.68 to 5.77). Spontaneous deliveries were 75, 16 were instrumental vaginal (one forceps and 15 ventouse) and eight were cesarean deliveries. Head-perineum distance was associated with spontaneous delivery with AUC=0.68 (95% CI; 0.55 to 0.80) and angle of progression with AUC=0.67 (95% CI; 0.55 to 0.80). Ultrasound measurement of cervical dilatation or position at inclusion were not significantly associated with a spontaneous delivery. Conclusions Ultrasound examinations showed that fetal head station and cervical dilatation was associated with the duration of labor but measurements of fetal head station were the variables best associated with operative deliveries.