Fetal molding examined with transperineal ultrasound and associations with position and delivery mode

Sonographic evaluation of the fetal head position and attitude during labor

Fetal malpresentation, malposition, and asynclitism are among the most common determinants of a protracted active phase of labor, arrest of dilatation during the first stage, and arrest of descent in the second stage. The diagnosis of these conditions is traditionally based on vaginal examination, which is subjective and poorly reproducible. Intrapartum sonography has been demonstrated to yield higher accuracy than vaginal examination in characterizing fetal malposition, and some guidelines endorse its use for the verification of the occiput position before performing an instrumental delivery. It is also useful for the objective diagnosis of the malpresentation or asynclitism of the fetal head. According to our experience, the sonographic assessment of the head position in labor is simple to perform also for clinicians with basic ultrasound skills, whereas the assessment of malpresentation and asynclitism warrants a higher level of expertise. When clinically appropriate, the fetal occiput position can be easily ascertained using transabdominal sonography combining the axial and the sagittal planes. With the transducer positioned on the maternal suprapubic region, the fetal head can be visualized, and landmarks including the fetal orbits, the midline, and the occiput itself with the cerebellum and the cervical spine (depending on the type of fetal position) can be demonstrated below the probe. Sinciput, brow, and face represent the 3 "classical" variants of cephalic malpresentation and are characterized by a progressively increasing degree of deflexion from vertex presentation. Transabdominal sonography has been recently suggested for the objective assessment of the fetal head attitude when a cephalic malpresentation is clinically suspected. Fetal attitude can be evaluated on the sagittal plane with either a subjective or an objective approach. Two different sonographic parameters such as the occiput-spine angle and the chin-chest angle have been recently described to quantify the degree of flexion in fetuses in non-occiput-posterior or occiput-posterior position, respectively. Finally, although clinical examination still represents the mainstay of diagnosis of asynclitism, the use of intrapartum sonography has been shown to confirm the digital findings. The sonographic diagnosis of asynclitism can be achieved in expert hands using a combination of transabdominal and transperineal sonography. At suprapubic sonography on the axial plane only, 1 orbit can be visualized (squint sign) while the sagittal suture appears anteriorly (posterior asynclitism) or posteriorly (anterior asynclitism) displaced. Eventually the transperineal approach does not allow the visualization of the cerebral midline on the axial plane if the probe is perpendicular to the fourchette. In this expert review we summarize the indications, technique, and clinical role of intrapartum sonographic evaluation of fetal head position and attitude.

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 sonopartogram

The assessment of labor progress from digital vaginal examination has remained largely unchanged for at least a century, despite the current major advances in maternal and perinatal care. Although inconsistently reproducible, the findings from digital vaginal examination are customarily plotted manually on a partogram, which is composed of a graphical representation of labor, together with maternal and fetal observations. The partogram has been developed to aid recognition of failure to labor progress and guide management-specific obstetrical intervention. In the last decade, the use of ultrasound in the delivery room has increased with the advent of more powerful, portable ultrasound machines that have become more readily available for use. Although ultrasound in intrapartum practice is predominantly used for acute management, an ultrasound-based partogram, a sonopartogram, might represent an objective tool for the graphical representation of labor. Demonstrating greater accuracy for fetal head position and more objectivity in the assessment of fetal head station, it could be considered complementary to traditional clinical assessment. The development of the sonopartogram concept would require further undertaking of serial measurements. Advocates of ultrasound will concede that its use has yet to demonstrate a difference in obstetrical and neonatal morbidity in the context of the management of labor and delivery. Taking a step beyond the descriptive graphical representation of labor progress is the question of whether a specific combination of clinical and demographic parameters might be used to inform knowledge of labor outcomes. Intrapartum cesarean deliveries and deliveries assisted by forceps and vacuum are all associated with a heightened risk of maternal and perinatal adverse outcomes. Although these outcomes cannot be precisely predicted, many known risk factors exist. Malposition and high station of the fetal head, short maternal stature, and other factors, such as caput succedaneum, are all implicated in operative delivery; however, the contribution of individual parameters based on clinical and ultrasound assessments has not been quantified. Individualized risk prediction models, including maternal characteristics and ultrasound findings, are increasingly used in women's health-for example, in preeclampsia or trisomy screening. Similarly, intrapartum cesarean delivery models have been developed with good prognostic ability in specifically selected populations. For intrapartum ultrasound to be of prognostic value, robust, externally validated prediction models for labor outcome would inform delivery management and allow shared decision-making with parents.

Manipulative Reduction for Abnormal Uterine Inclination in Vaginal Delivery

Objective

To investigate the manipulative reduction in abnormal uterine inclination in vaginal delivery.

Methods

With the independently developed uterine inclination surveyor, 40 primiparas with abnormal uterine inclination were randomly divided into two groups: treatment group (Group A, 20 cases) and control group (Group B, 20 cases). The general condition of the primipara, the labor stages, the changes in uterine inclination after treatment, postpartum hemorrhage at 2 hours, and the general condition of fetuses were observed to study the therapeutic value of manual reduction in abnormal uterine inclination.

Result

In the control group, one uterine inclination was not corrected with the change in labor process, and the pregnancy was terminated due to stagnation of the active phase. In the first stage of labor, the time spent in the treatment group (393.4 ± 31.3 mins) was significantly lower than that in the control group (440.7 ± 34.9 mins) (P = 0.001). Compared with the control group (49.8 ± 6.5 mins), the treatment group (42.6 ± 7.2 mins) also exhibited a significantly shortened second stage of labor (P = 0.02). Sixteen cases (16/20) in the treatment group returned to normal after manual reduction, and 9 cases (9/20) in the control group returned to normal with the progression of natural labor. Manual reduction could be used as an option to treat abnormal uterine inclination (P = 0.01). There was no significant difference in the third stage of labor (P = 0.2), 2-hour postpartum hemorrhage (P = 0.35), Apgar score (P = 0.64), or body weight (P = 0.76) between the two groups.

Conclusion

Manual reduction in the treatment of abnormal uterine inclination has obvious effects, shortens the birth process, and is safe for the fetus.

Fetal head descent assessed by transabdominal ultrasound: a prospective observational study

BACKGROUND

Determining fetal head descent, expressed as fetal head station and engagement is an essential part of monitoring progression in labor. Assessing fetal head station is based on the distal part of the fetal skull, whereas assessing engagement is based on the proximal part. Prerequisites for assisted vaginal birth are that the fetal head should be engaged and its lowermost part at or below the level of the ischial spines. The part of the fetal head above the pelvic inlet reflects the true descent of the largest diameter of the skull. In molded (reshaped) fetal heads, the leading bony part of the skull may be below the ischial spines while the largest diameter of the fetal skull still remains above the pelvic inlet. An attempt at assisted vaginal birth in such a situation would be associated with risks. Therefore, the vaginal or transperineal assessments of station should be supplemented with a transabdominal examination. We suggest a method for the assessment of fetal head descent with transabdominal ultrasound.

OBJECTIVE

To investigate the correlation between transabdominal and transperineal assessment of fetal head descent, and to study fetal head shape at different labor stages and head positions.

STUDY DESIGN

Women with term singleton cephalic pregnancies admitted to the labor ward for induction of labor or in spontaneous labor, at the Cairo University Hospital and Oslo University Hospital from December 2019 to December 2020 were included. Fetal head descent was assessed with transabdominal ultrasound as the suprapubic descent angle between a longitudinal line through the symphysis pubis and a line from the upper part of the symphysis pubis extending tangentially to the fetal skull. We compared measurements with transperineally assessed angle of progression and investigated interobserver agreement. We also measured the part of fetal head above and below the symphysis pubis at different labor stages.

RESULTS

The study population comprised 123 women, of whom 19 (15%) were examined before induction of labor, 8 (7%) in the latent phase, 52 (42%) in the active first stage and 44 (36%) in the second stage. The suprapubic descent angle and the angle of progression could be measured in all cases. The correlation between the transabdominal and transperineal measurements was -0.90 (95% confidence interval, -0.86 to -0.93). Interobserver agreement was examined in 30 women and the intraclass correlation coefficient was 0.98 (95% confidence interval, 0.95-0.99). The limits of agreement were from -9.5 to 7.8 degrees. The fetal head was more elongated in occiput posterior position than in non-occiput posterior positions in the second stage of labor.

CONCLUSION

We present a novel method of examining fetal head descent by assessing the proximal part of the fetal skull with transabdominal ultrasound. The correlation with transperineal ultrasound measurements was strong, especially early in labor. The fetal head was elongated in the occiput posterior position during the second stage of labor.

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.