Sonographic diagnosis of fetal head deflexion and the risk of cesarean delivery

Descent of the presenting part assessed with ultrasound

Fetal head descent can be expressed as fetal station and engagement. Station is traditionally based on clinical vaginal examination of the distal part of the fetal skull and related to the level of the ischial spines. Engagement is based on a transabdominal examination of the proximal part of the fetal head above the pelvic inlet. Clinical examinations are subjective, and objective measurements of descent are warranted. Ultrasound is a feasible diagnostic tool in labor, and fetal lie, station, position, presentation, and attitude can be examined. This review presents an overview of fetal descent examined with ultrasound. Ultrasound was first introduced for examining fetal descent in 1977. The distance from the sacral tip to the fetal skull was measured with A-mode ultrasound, but more convenient transperineal methods have since been published. Of those, progression distance, angle of progression, and head-symphysis distance are examined in the sagittal plane, using the inferior part of the symphysis pubis as reference point. Head-perineum distance is measured in the frontal plane (transverse transperineal scan) as the shortest distance from perineum to the fetal skull, representing the remaining part of the birth canal for the fetus to pass. At high stations, the fetal head is directed downward, followed with a horizontal and then an upward direction when the fetus descends in the birth canal and deflexes the head. Head descent may be assessed transabdominally with ultrasound and measured as the suprapubic descent angle. Many observational studies have shown that fetal descent assessed with ultrasound can predict labor outcome before induction of labor, as an admission test, and during the first and second stage of labor. Labor progress can also be examined longitudinally. The International Society of Ultrasound in Obstetrics and Gynecology recommends using ultrasound in women with prolonged or arrested first or second stage of labor, when malpositions or malpresentations are suspected, and before an operative vaginal delivery. One single ultrasound parameter cannot tell for sure whether an instrumental delivery is going to be successful. Information about station and position is a prerequisite, but head direction, presentation, and attitude also should be considered.

The head direction to the angle of progression ratio: a quantitative parameter for intrapartum evaluation of cephalic malposition

BACKGROUND

No previous study has evaluated the transitions of intrapartum transperineal ultrasound parameters during labor progression in cephalic malposition.

OBJECTIVE

We aimed to quantitate the characteristic trends of fetal head position and descent in cephalic malposition by analyzing the transitions of intrapartum transperineal ultrasound parameters and explore an indicator associated with the degree of cephalic malposition.

STUDY DESIGN

We retrospectively analyzed pregnant women who delivered at term from January 2018 to December 2020 at the University of Tokyo Hospital. The fetal occipital position was classified as occiput anterior and nonocciput anterior according to the fetal occipital angle of 0° to 75° and 75° to 180°, respectively. Fetal occipital angle was defined by the midline angle and position of the ocular orbit. The differences in the trends of head direction, head-symphysis distance, and progression distance relative to the angle of progression between occiput anterior and nonocciput anterior cases were evaluated. In addition, the parameters that showed differences were analyzed to evaluate their relationship to the degree of cephalic malposition.

RESULTS

A total of 502 images (occiput anterior, 319; nonocciput anterior, 183) met the inclusion criteria. The distribution of head direction values relative to the angle of progression was smaller in the nonocciput anterior group than in the occiput anterior group, whereas the head-symphysis distance and progression distance values relative to the angle of progression showed no difference in their distribution between the occiput anterior and nonocciput anterior groups. The ratio of head direction to the angle of progression was significantly smaller in the nonocciput anterior group than in the occiput anterior group (median [interquartile range], 0.03 [-0.02 to 0.10] vs 0.21 [0.12-0.28]; P<.0001). Furthermore, this ratio was negatively correlated with fetal occipital angle (Spearman correlation coefficient, -0.66).

CONCLUSION

Our results indicated that the head direction to angle of progression ratio reflects the deviation in the fetal head direction toward the maternal dorsal side, and decreases in proportion to the degree of cephalic malposition. This concept of deviation in the head direction as an indicator for evaluating cephalic malposition with intrapartum transperineal ultrasound may contribute to improving labor management in the case of cephalic malposition.

Ultrasound in labor: clinical practice guideline and recommendation by the WAPM-World Association of Perinatal Medicine and the PMF-Perinatal Medicine Foundation

This recommendation document follows the mission of the World Association of Perinatal Medicine in collaboration with the Perinatal Medicine Foundation. We aim to bring together groups and individuals throughout the world for standardization to implement the ultrasound evaluation in labor ward and improve the clinical management of labor. Ultrasound in labor can be performed using a transabdominal or a transperineal approach depending upon which parameters are being assessed. During transabdominal imaging, fetal anatomy, presentation, liquor volume, and placental localization can be determined. The transperineal images depict images of the fetal head in which calculations to determine a proposed fetal head station can be made.

Intrapartum sonographic assessment of the fetal head flexion in protracted active phase of labor and association with labor outcome: a multicenter, prospective study

BACKGROUND

To date, no research has focused on the sonographic quantification of the degree of flexion of the fetal head in relation to the labor outcome in women with protracted active phase of labor.

OBJECTIVE

This study aimed to assess the relationship between the transabdominal sonographic indices of fetal head flexion and the mode of delivery in women with protracted active phase of labor.

STUDY DESIGN

Prospective evaluation of women with protracted active phase of labor recruited across 3 tertiary maternity units. Eligible cases were submitted to transabdominal ultrasound for the evaluation of the fetal head position and flexion, which was measured by means of the occiput-spine angle in fetuses in nonocciput posterior position and by means of the chin-to-chest angle in fetuses in occiput posterior position. The occiput-spine angle and the chin-to-chest angle were compared between women who had vaginal delivery and those who had cesarean delivery. Cases where obstetrical intervention was performed solely based on suspected fetal distress were excluded.

RESULTS

A total of 129 women were included, of whom 43 (33.3%) had occiput posterior position. Spontaneous vaginal delivery, instrumental delivery, and cesarean delivery were recorded in 66 (51.2%), 17 (13.1%), and 46 (35.7%) cases, respectively. A wider occiput-spine angle was measured in women who had vaginal delivery compared with those submitted to cesarean delivery owing to labor dystocia (126±14 vs 115±24; P<.01). At the receiver operating characteristic curve, the area under the curve was 0.675 (95% confidence interval, 0.538-0.812; P<.01), and the optimal occiput-spine angle cutoff value discriminating between cases of vaginal delivery and those delivered by cesarean delivery was 109°. A narrower chin-to-chest angle was measured in cases who had vaginal delivery compared with those undergoing cesarean delivery (27±33 vs 56±28 degrees; P<.01). The area under the curve of the chin-to-chest angle in relation to the mode of delivery was 0.758 (95% confidence interval, 0.612-0.904; P<.01), and the optimal cutoff value discriminating between vaginal delivery and cesarean delivery was 33.0°.

CONCLUSION

In women with protracted active phase of labor, the sonographic demonstration of fetal head deflexion in occiput posterior and in nonocciput posterior fetuses is associated with an increased incidence of cesarean delivery owing to labor dystocia. Such findings suggest that intrapartum ultrasound may contribute in the categorization of the etiology of labor dystocia.

Intrapartum ultrasound for the diagnosis of cephalic malpositions and malpresentations

Fetuses with malpresentation and malposition during labor represent important clinical challenges. Women with fetuses presenting with malpresentation or malposition are at risk of increased perinatal complications, such as cesarean delivery, failure of operative vaginal delivery, neonatal acidemia, and neonatal intensive care admission. Intrapartum ultrasound has been found to be more reliable than digital examination in assessing malpresentation and malposition. The use of intrapartum ultrasound to assess fetal position and presentation, in addition to fetal attitude, to predict and aid in decision making regarding delivery can help in improving management decision making. Cephalic malpresentation and malposition is a unique subset of fetal orientation and can benefit from intrapartum ultrasound identification and assessment for delivery.

The role of the angle of progression in the prediction of the outcome of occiput posterior position in the second stage of labor

BACKGROUND

Occiput posterior position is the most frequent cephalic malposition, and its persistence at delivery is associated with a higher risk of maternal and perinatal morbidity. Diagnosis and management of occiput posterior position remain a clinical challenge. This is partly caused by our inability to predict fetuses who will spontaneously rotate into occiput anterior from those who will have persistent occiput posterior position. The angle of progression, measured with transperineal ultrasound, represents a reliable tool for the evaluation of fetal head station during labor. The relationship between the persistence of occiput posterior position and fetal head station in the second stage of labor has not been previously assessed.

OBJECTIVE

This study aimed to evaluate the role of fetal head station, as measured by the angle of progression, in the prediction of persistent occiput posterior position and the mode of delivery in the second stage of labor.

STUDY DESIGN

We recruited a nonconsecutive series of women with posterior occiput position diagnosed by transabdominal ultrasound in the second stage of labor. For each woman, a transperineal ultrasound was performed to measure the angle of progression at rest. We compared the angle of progression between women who delivered fetuses in occiput anterior position and those with persistent occiput posterior position at delivery. Receiver operating characteristics curves were performed to evaluate the accuracy of the angle of progression in the prediction of persistent occiput posterior position. Finally, we performed a multivariate logistic regression to determine independent predictors of persistent occiput posterior position.

RESULTS

Overall, 63 women were included in the analysis. Among these, 39 women (62%) delivered in occiput anterior position, whereas 24 (38%) delivered in occiput posterior position (persistent occiput posterior position). The angle of progression was significantly narrower in the persistent occiput posterior position group than in women who delivered fetuses in occiput anterior position (118.3°±12.2° vs 127.5°±10.5°; P=.003). The area under the receiver operating characteristics curve was 0.731 (95% confidence interval, 0.594-0.869) with an estimated best cutoff range of 121.5° (sensitivity of 72% and specificity of 67%). On logistic regression analysis, the angle of progression was found to be independently associated with persistence of occiput posterior position (odds ratio, 0.942; 95% confidence interval, 0.889-0.998; P=.04). Finally, women who underwent cesarean delivery had significantly narrower angle of progression than women who had a vaginal delivery (113.5°±8.1 vs 128.0°±10.7; P<.001). The area under the receiver operating characteristics curve for the prediction of cesarean delivery was 0.866 (95% confidence interval, 0.761-0.972). At multivariable logistic regression analysis including the angle of progression, parity, and gestational age at delivery, the angle of progression was found to be the only independent predictor associated with cesarean delivery (odds ratio, 0.849; 95% confidence interval, 0.775-0.0930; P<.001).

CONCLUSION

In fetuses with occiput posterior at the beginning of the second stage of labor, narrower values of the angle of progression are associated with higher rates of persistent occiput posterior position at delivery and a higher risk of cesarean delivery.

There are 4, not 7, cardinal movements in labor

The mechanics of labor describe the forces required for fetal descent, and the movements that the fetus must perform to overcome the resistance met by the maternal bony pelvis and soft tissue. The fetus negotiates the birth canal and rotational movements are necessary for descent. Anglo-American literature lists 7 cardinal movements, namely engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion. German and older English literature lists only 4 rotational movements as the cardinal movements and excludes engagement, descent, and expulsion. We would argue that descent is the main purpose of the uterine powers and cardinal movements, a description of the rotational movements the fetal head and shoulders must perform to obtain descent. Ultrasound offers a historically unique opportunity for noninvasive, dynamic studies of the mechanics of labor. The information gathered by clinical examination and ultrasound should be integrated into clinical decision making.