Descent of fetal head during active pushing: secondary analysis of prospective cohort study investigating ultrasound examination before operative vaginal delivery

OBJECTIVES

To investigate if descent of the fetal head during active pushing is associated with duration of operative vaginal delivery, mode of delivery and neonatal outcome in nulliparous women with prolonged second stage of labor.

METHODS

This was a prospective cohort study of nulliparous women with prolonged second stage of labor, conducted between November 2013 and July 2016 in five European countries. Fetal head descent was measured using transperineal ultrasound. Head-perineum distance (HPD) was measured between contractions and on maximum contraction during active pushing, and the difference between these values (ΔHPD) was calculated. The main outcome was duration of operative vaginal delivery, estimated using survival analysis to calculate hazard ratios (HRs) for vaginal delivery, with values > 1 indicating a shorter duration. HR was adjusted for prepregnancy body mass index, maternal age, induction of labor, augmentation with oxytocin and use of epidural analgesia. Pregnancies were grouped according to ΔHPD quartile, and delivery mode and neonatal outcome were compared between groups.

RESULTS

The study population comprised 204 women. Duration of vacuum extraction was shorter with increasing ΔHPD. Estimated mean duration was 10.0, 9.0, 8.8 and 7.5 min in pregnancies with ΔHPD in the first to fourth quartiles, respectively, and the adjusted HR for vaginal delivery, using increasing ΔHPD as a continuous variable, was 1.04 (95% CI, 1.01-1.08). Mean ΔHPD was 7 mm (range, -10 to 37 mm). ΔHPD was either negative or ≤ 2 mm in the lowest quartile. In this group, 7/50 (14%) pregnancies were delivered by Cesarean section, compared with 8/154 (5%) of those with ΔHPD > 2 mm (P < 0.05). There was no significant association between umbilical artery pH < 7.10 or 5-min Apgar score < 7 and ΔHPD quartile.

CONCLUSION

Minimal or no fetal head descent during active pushing was associated with longer duration of operative vaginal delivery and higher frequency of Cesarean section in nulliparous women with prolonged second stage of labor. © 2019 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Prediction of delivery mode by ultrasound-assessed fetal position in nulliparous women with prolonged first stage of labor

OBJECTIVES

To ascertain if fetal head position on transabdominal ultrasound is associated with delivery by Cesarean section in nulliparous women with a prolonged first stage of labor.

METHODS

This was a prospective observational study performed at Stavanger University Hospital, Norway, and Addenbrooke's Hospital, Cambridge, UK, between January 2012 and April 2013. Nulliparous pregnant women with a singleton cephalic presentation at term and prolonged labor had fetal head position assessed by ultrasound. The main outcome was Cesarean section vs vaginal delivery, and secondary outcomes were association of fetal head position with operative vaginal delivery and duration of remaining time in labor.

RESULTS

Fetal head position was assessed successfully by ultrasound examination in 142/150 (95%) women. In total, 19/50 (38%) women with a fetus in the occiput posterior (OP) position were delivered by Cesarean section compared with 16/92 (17%) women with a fetus in a non-OP position (P = 0.01). On multivariable logistic regression analysis, the OP position predicted delivery by Cesarean section with an odds ratio (OR) of 2.9 (95% CI, 1.3-6.7; P = 0.01) and induction of labor with an OR of 2.4 (95% CI, 1.0-5.6; P = 0.05). Fetal head position was not associated with operative vaginal delivery or with remaining time in labor. The agreement between a digital and an ultrasound assessment of OP position was poor (Cohen's kappa = 0.19; P = 0.18).

CONCLUSION

OP fetal head position assessed by transabdominal ultrasound was significantly associated with delivery by Cesarean section.

Comparison between ultrasound parameters and clinical examination to assess fetal head station in labor

OBJECTIVE

Several ultrasound parameters, including intrapartum transperineal ultrasound (ITU) head station, angle of progression (AOP), head-perineum distance (HPD) and head-symphysis distance (HSD), have been suggested to assess fetal head station during labor. The aim of this study was to analyze the relationship between these ultrasound parameters and to compare them with digital palpation.

METHODS

We analyzed 106 stored volume dataset pairs that had been acquired at Stavanger University Hospital, Norway, from nulliparous women at term with prolonged first stage of labor. The volumes were acquired using a three-dimensional transducer applied between the labia majora in a mid-sagittal plane and perineally in a transverse plane. Digitally palpated head station and cervical dilatation were also noted. The results were compared using regression and correlation coefficients.

RESULTS

There were good correlations between ITU head station and HPD (r = 0.71), between ITU head station and HSD (r = 0.74) and between HSD and HPD (r = 0.75). Palpated head station showed only moderate correlation with ITU head station (r = 0.52). Cervical dilatation showed a weak correlation with ITU head station (r = 0.30).

CONCLUSION

The ultrasound parameters showed a high degree of correlation with each other, but only moderate correlation to vaginally palpated fetal head station.

Agreement between two- and three-dimensional transperineal ultrasound methods in assessing fetal head descent in the first stage of labor

OBJECTIVE

To study intraobserver repeatability and intermethod agreement between two- (2D) and three-dimensional (3D) transperineal ultrasound methods in assessing fetal head descent during the first stage of labor.

METHODS

Fetal head descent was measured with transperineal ultrasound as the fetal head-perineum distance and the angle of progression in 106 primiparous women with prolonged first stage of labor. A single obstetrician performed all the scans, and another obstetrician analyzed the acquired 2D images and 3D volumes, blinded to clinical assessments and labor outcome. Intraobserver repeatability and intermethod agreement between 2D and 3D methods were analyzed.

RESULTS

The repeatability coefficient was ± 4.1 mm in 2D acquisitions and ± 1.7 mm in 3D acquisitions of fetal head-perineum distance. The intraclass correlation coefficients (ICC) were 0.94 for 2D and 0.99 for 3D measurements. The angle of progression repeatability coefficients were ± 6.7° using 2D and ± 5.7° using 3D ultrasound and ICCs were 0.91 and 0.94, respectively. The intermethod ICC for fetal head-perineum distance in 2D vs 3D acquisitions was 0.95 and for angle of progression it was 0.93; the intermethod 95% limits of agreement were - 5.8 mm to + 7.2 mm and - 8.9° to + 13.7°, respectively. Cohen's kappa for 2D vs 3D acquisitions was 0.85 using 40 mm as a cut-off level for fetal head-perineum distance and 0.79 using 110° as cut-off level for angle of progression.

CONCLUSIONS

For one ultrasound operator the intraobserver repeatability and agreement between 2D and 3D ultrasound methods in prolonged first stage of labor were good. Given that 2D methods are simpler to learn and can be analyzed quickly online, 2D equipment might therefore be preferred in the labor room.

Prediction of delivery mode with transperineal ultrasound in women with prolonged first stage of labor

OBJECTIVE

To investigate if fetal head-perineum distance and angle of progression measured with two-dimensional (2D) and three-dimensional (3D) transperineal ultrasound could predict outcome of labor in primiparous women with prolonged first stage of labor.

METHODS

This was a prospective observational study of 110 primiparous women with singleton cephalic presentation at term diagnosed with prolonged first stage of labor. Digital assessment of fetal station was related to the ischial spine. Fetal head descent was measured with transperineal ultrasound as the shortest distance from the fetal head to the perineum, and the angle between the pubic symphysis and the fetal head. Receiver-operating characteristics (ROC) curves were constructed and 2D and 3D data acquisitions were compared. The stored 3D volumes were assessed by an examiner blinded to all other data. Vaginal delivery vs. Cesarean section was the primary outcome.

RESULTS

Cesarean section was performed in 25% of the women. Areas under the ROC curves for prediction of vaginal delivery were 81% (95% confidence interval (CI), 71-91%) (P < 0.01) and 76% (95% CI, 66-87%) (P < 0.01) for fetal head-perineum distance and angle of progression, respectively, as measured by 2D ultrasound and 66% (95% CI, 54-79%) for digital assessment of fetal station (P = 0.01). In 50% of women fetal head-perineum distance was ≤ 40 mm and 93% (95% CI, 83-97%) of them delivered vaginally vs. 18% (95% CI, 5-48%) with distance > 50 mm. In 48% of women the angle of progression was ≥ 110° and 87% (95% CI, 75-93%) of them delivered vaginally vs. 38% (95% CI, 21-57%) with angle < 100°. Results from 2D and 3D acquisitions were similar.

CONCLUSION

Fetal head-perineum distance and angle of progression measured with 2D or 3D ultrasound can predict labor outcome, with similar predictive values for the two techniques.