Transabdominal and transperineal ultrasound vs routine care before instrumental vaginal delivery - A randomized controlled trial

The use of intrapartum ultrasound in operative vaginal birth: a retrospective cohort study

BACKGROUND

Poor outcomes from operative vaginal birth have been associated with failure to recognize malposition, breakdown in interdisciplinary communication, and deviation from accepted guidelines. We recently implemented a safety bundle including routine intrapartum ultrasound and a structured time-out and procedural checklist aiming to reduce maternal and perinatal morbidity from operative vaginal birth.

OBJECTIVE

This study aimed to compare births where intrapartum ultrasound was used and those where it was not used during a safety bundle implementation period at Monash Health.

STUDY DESIGN

We performed a retrospective cohort study at Monash Health during the transitional phase of implementing an operative vaginal birth safety bundle. We studied all women with operative vaginal birth and fully dilated cesarean delivery with a singleton cephalic term fetus. We compared births for which intrapartum ultrasound was used and those for which it was not. The primary outcome was neonates delivered in an unexpected position. Neonatal and maternal morbidity were also assessed, including a neonatal composite of Apgar score <7 at 5 minutes, cord lactate >8 mmol/L, need for resuscitation, significant birth trauma, or neonatal intensive care unit admission. To control for confounding by indication, we estimated propensity scores for the probability of using intrapartum ultrasound for each case based on maternal and labor characteristics, and adjusted the effect estimates for the propensity scores using multivariable logistic regression models.

RESULTS

From August 2022 to July 2023, there were 1205 operative vaginal births or fully dilated cesarean deliveries at Monash Health, including 743 (61.7%) forceps, 346 (28.7%) vacuum, and 116 (9.6%) fully dilated cesarean deliveries. Over this time, we observed increased uptake of intrapartum ultrasound from 26% in August 2022 to 60% (P<.001) in July 2023, of the time-out from 21% to 58% (P<.001), and the checklist from 33% to 80% (P<.001) of operative second-stage births. Among the births where intrapartum ultrasound was used (n=509), compared with those where it was not (n=696), there were significantly more forceps births (67% vs 58%; adjusted odds ratio, 1.35; 95% confidence interval, 1.05-1.74; P=.021) and a reduction in vacuum births (24% vs 32%; adjusted odds ratio, 0.77; 95% confidence interval, 0.58-1.01; P=.059). There were no significant differences in fully dilated cesarean delivery or maternal morbidity. Intrapartum ultrasound use was associated with significantly fewer infants being delivered in an unexpected position (0.2% vs 2.2%; adjusted odds ratio, 0.08; 95% confidence interval, 0.00-0.44; P=.019) and a significant reduction in composite neonatal morbidity (22% vs 25%; adjusted odds ratio, 0.73; 95% confidence interval, 0.54-0.97; P=.031).

CONCLUSION

During the implementation of a safety bundle, the use of ultrasound before operative vaginal birth was associated with fewer infants delivered in an unexpected position and reduced neonatal morbidity.

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.

Intrapartum transperineal ultrasound: angle of progression to evaluate and predict the mode of delivery and labor progression

Intrapartum ultrasonography serves as a valuable tool for the objective evaluation of labor progression and effectively identifies underlying factors, such as asynclitism, in cases of abnormal labor progression. Among the various ultrasound measurement techniques, the angle of progression (AOP) demonstrates favorable reproducibility and accuracy in assessing fetal head descent. In the context of abnormal labor, interventions differ across different stages of labor, emphasizing the importance of investigating the utility of AOP according to labor stages in this review article. Pre-labor assessment of AOP can be beneficial in terms of counseling for the timing of induction of labor, while a wider AOP value during the prolonged first stage of labor has demonstrated a positive correlation with successful vaginal delivery and shorter time to delivery. In the second stage of labor, the AOP has exhibited efficacy in predicting the mode of delivery and complicated operative deliveries. Furthermore, it has assisted in predicting the duration of labor, thereby highlighting its potential as a decision-making model for labor progression. However, further research is needed to investigate aspects, such as the determination of cutoff values, of AOP, considering the multifaceted characteristics of labor progression, which are influenced by complex interactions among maternal, fetal, and other contributing factors.

Head-to-perineum distance measured transperineally as a predictor of failed midcavity vacuum-assisted delivery

BACKGROUND

During the second stage of labor, in case of a need for a fetal extraction at midcavity, the choice of attempting the procedure between operative vaginal delivery and cesarean delivery is difficult. Moreover, guidelines on this subject are not clear.

OBJECTIVE

This study aimed to identify antenatal and intrapartum parameters associated with a failed midcavity vacuum-assisted delivery and its association with maternal and neonatal adverse outcomes.

STUDY DESIGN

This was a single-center, retrospective, cohort study conducted at a tertiary maternity hospital in France from January 2010 to December 2020. Women with singleton pregnancies under epidural analgesia with nonanomalous cephalic presenting fetuses and gestational ages at ≥37 weeks of gestation, who were submitted to midcavity vacuum-assisted delivery, were included. Following the American College of Obstetricians and Gynecologists definition, midcavity was defined as the presenting part of the fetus (ie, the fetal head) found at stations 0 and +1. For research purposes, all patients were submitted to transperineal ultrasound to evaluate the head-to-perineum distance, however, this measurement did not affect the decision to perform a midcavity vacuum-assisted delivery. The primary outcome of the study was failed midcavity vacuum-assisted delivery leading to cesarean delivery or the use of a different instrument to achieve vaginal delivery.

RESULTS

Overall, 951 cases of midcavity vacuum-assisted delivery were included in this study. Failed midcavity vacuum-assisted delivery occurred in 242 patients (25.4%). Factors independently associated with failed midcavity vacuum-assisted delivery included maternal height (adjusted odds ratio, 0.96; 95% confidence interval, 0.94-0.99; P=.002), duration of the active phase of the first stage of labor (adjusted odds ratio, 1.11; 95% confidence interval, 1.05-1.17; P<.001), nonocciput anterior fetal head position (adjusted odds ratio, 1.47; 95% confidence interval, 1.06-2.04; P=.02), z score of the head-to-perineum distance (adjusted odds ratio, 1.23; 95% confidence interval, 1.05-1.43; P=.01), and birthweight of >4000 g (adjusted odds ratio, 2.04; 95% confidence interval, 1.28-3.26; P=.003). Women submitted to a failed midcavity vacuum-assisted delivery were more likely to have a major postpartum hemorrhage (7.1% vs 2.0%; P<.001), whereas neonates were more likely to have an umbilical artery pH of <7.1 (30.5% vs 19.8%; P=.001), be admitted to the neonatal intensive care unit (9.6% vs 4.7%; P=.005), and have a severe caput succedaneum (14.9% vs 0.7%; P<.001). Subgroup analysis on all patients with a fetal head station of 0 found that the head-to-perineum distance was the only independent variable associated with failed midcavity vacuum-assisted delivery (adjusted odds ratio, 1.66; 95% confidence interval, 1.29-2.12; P<.001). The area under the receiving operating characteristic curve of the head-to-perineum distance in this subgroup population was 0.67 (95% confidence interval, 0.60-0.73; P<.001), and the optimal cutoff point of the head-to-perineum distance measurement discriminating between failed and successful midcavity vacuum-assisted deliveries was 55 mm. It was associated with a 0.90 (95% confidence interval, 0.83-0.95) sensitivity, 0.19 (95% confidence interval, 0.14-0.25) specificity, 0.36 (95% confidence interval, 0.30-0.42) positive predictive value, and 0.80 (95% confidence interval, 0.66-0.90) negative predictive value.

CONCLUSION

Study data showed that a high fetal head station, measured using the head-to-perineum distance, and a nonocciput anterior position of the fetal head are independently associated with failed midcavity vacuum-assisted delivery. The result supported the systematic assessment of the sonographic head station and position before performing a midcavity vacuum-assisted delivery.

Assessment of labor progress by ultrasound vs manual examination: a randomized controlled trial

BACKGROUND

Assessment of labor progress via digital examination is considered the standard of care in most delivery rooms. However, this method can be stressful, painful, and imprecise, and multiple examinations increase the risk for chorioamnionitis. Intrapartum ultrasound was found to be an objective, noninvasive tool to monitor labor progression.

OBJECTIVE

This study aimed to investigate whether, among nulliparous women, the use of intrapartum ultrasound can reduce the rate of intrapartum fever by reducing the number of digital examinations.

STUDY DESIGN

This was a prospective, randomized controlled trial in term nulliparas admitted with prelabor rupture of membranes, induction of labor, or in latent phase of labor with a cervical dilation of <4 cm. Women were randomized into 1 of the following 2 arms: (1) labor progress assessed by ultrasound, avoiding digital examinations as much as possible; and (2) control group in which labor progression was assessed according to the regular protocol. Before the study, all labor ward physicians underwent training in intrapartum ultrasound.

RESULTS

A total of 90 women were randomized to the ultrasound group and 92 were randomized to the control group. When compared with the control group, the ultrasound group had significantly lower rates of intrapartum fever (11.1% vs 26.1%; P=.01), clinical chorioamnionitis (3.3% vs 16.5%; P>.01), and histologic chorioamnionitis (2.2% vs 9.8%; P=.03). The median number of digital examinations was significantly lower in the ultrasound group (5; interquartile range, 4-6) than in the control group (8; interquartile range, 6-10; P<.01). The median number of digital examinations per hour in the ultrasound group was significantly lower than in the control group (0.2 vs 0.4; P<.01). The induction rates, time from admission to delivery, mode of delivery, Apgar score at 5 minutes, and neonatal intensive care unit admission rates did not differ significantly between the groups.

CONCLUSION

The use of intrapartum ultrasound lessens the total number of digital examinations needed to be performed during labor and, consequently, the incidence of intrapartum fever and chorioamnionitis are reduced. No adverse effects on labor progression and short-term maternal or neonatal outcomes were noted.

Sonographic knowledge of occiput position to decrease failed operative vaginal delivery: a systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

This study aimed to assess the efficacy of sonographic assessment of fetal occiput position before operative vaginal delivery to decrease the number of failed operative vaginal deliveries.

DATA SOURCES

The search was conducted in MEDLINE, Embase, Web of Science, Scopus, ClinicalTrial.gov, Ovid, and Cochrane Library as electronic databases from the inception of each database to April 2021. No restrictions for language or geographic location were applied.

STUDY ELIGIBILITY CRITERIA

Selection criteria included randomized controlled trails of pregnant women randomized to either sonographic or clinical digital diagnosis of fetal occiput position during the second stage of labor before operative vaginal delivery.

METHODS

The primary outcome was failed operative vaginal delivery, defined as a failed fetal operative vaginal delivery (vacuum or forceps) extraction requiring a cesarean delivery or forceps after failed vacuum. The summary measures were reported as relative risks or as mean differences with 95% confidence intervals using the random effects model of DerSimonian and Laird. An I² (Higgins I²) >0% was used to identify heterogeneity.

RESULTS

A total of 4 randomized controlled trials including 1007 women with singleton, term, cephalic fetuses randomized to either the sonographic (n=484) or clinical digital (n=523) diagnosis of occiput position during the second stage of labor before operative vaginal delivery were included. Before operative vaginal delivery, fetal occiput position was diagnosed as anterior in 63.5% of the sonographic diagnosis group vs 69.5% in the clinical digital diagnosis group (P=.04). There was no significant difference in the rate of failed operative vaginal deliveries between the sonographic and clinical diagnosis of occiput position groups (9.9% vs 8.2%; relative risk, 1.14; 95% confidence interval, 0.77-1.68). Women randomized to sonographic diagnosis of occiput position had a significantly lower rate of occiput position discordance between the evaluation before operative vaginal delivery and the at birth evaluation when compared with those randomized to the clinical diagnosis group (2.3% vs 17.7%; relative risk, 0.16; 95% confidence interval, 0.04-0.74; P=.02). There were no significant differences in any of the other secondary obstetrical and perinatal outcomes assessed.

CONCLUSION

Sonographic knowledge of occiput position before operative vaginal delivery does not seem to have an effect on the incidence of failed operative vaginal deliveries despite better sonographic accuracy in the occiput position diagnosis when compared with clinical assessment. Future studies should evaluate how a more accurate sonographic diagnosis of occiput position or other parameters can lead to a safer and more effective operative vaginal delivery technique.

Routine vaginal examinations compared to other methods for assessing progress of labour to improve outcomes for women and babies at term

BACKGROUND

Routine vaginal examinations are undertaken at regular time intervals during labour to assess whether labour is progressing as expected. Unusually slow progress can be due to underlying problems, described as labour dystocia, or can be a normal variation of progress. Evidence suggests that if mother and baby are well, length of labour alone should not be used to decide whether labour is progressing normally. Other methods to assess labour progress include intrapartum ultrasound and monitoring external physical and behavioural cues. Vaginal examinations can be distressing for women, and overdiagnosis of dystocia can result in iatrogenic morbidity due to unnecessary intervention. It is important to establish whether routine vaginal examinations are effective, both as an accurate measure of physiological labour progress and to distinguish true labour dystocia, or whether other methods for assessing labour progress are more effective. This Cochrane Review is an update of a review first published in 2013.

OBJECTIVES

To compare the effectiveness, acceptability, and consequences of routine vaginal examinations compared with other methods, or different timings, to assess labour progress at term.

SEARCH METHODS

For this update, we searched Cochrane Pregnancy and Childbirth Trials Register (which includes trials from CENTRAL, MEDLINE, Embase, CINAHL, and conference proceedings) and ClinicalTrials.gov (28 February 2021). We also searched the reference lists of retrieved studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of vaginal examinations compared with other methods of assessing labour progress and studies assessing different timings of vaginal examinations. Quasi-RCTs and cluster-RCTs were eligible for inclusion. We excluded cross-over trials and conference abstracts.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed all studies identified by the search for inclusion in the review. Four review authors independently extracted data. Two review authors assessed risk of bias and certainty of the evidence using GRADE.

MAIN RESULTS

We included four studies that randomised a total of 755 women, with data analysed for 744 women and their babies. Interventions used to assess labour progress were routine vaginal examinations, routine ultrasound assessments, routine rectal examinations, routine vaginal examinations at different frequencies, and vaginal examinations as indicated. We were unable to conduct meta-analysis as there was only one study for each comparison.  All studies were at high risk of performance bias due to difficulties with blinding. We assessed two studies as high risk of bias and two as low or unclear risk of bias for other domains. The overall certainty of the evidence assessed using GRADE was low or very low.  Routine vaginal examinations versus routine ultrasound to assess labour progress (one study, 83 women and babies) Study in Turkey involving multiparous women with spontaneous onset of labour. Routine vaginal examinations may result in a slight increase in pain compared to routine ultrasound (mean difference -1.29, 95% confidence interval (CI) -2.10 to -0.48; one study, 83 women, low certainty evidence) (pain measured using a visual analogue scale (VAS) in reverse: zero indicating 'worst pain', 10 indicating no pain). The study did not assess our other primary outcomes: positive birth experience; augmentation of labour; spontaneous vaginal birth; chorioamnionitis; neonatal infection; admission to neonatal intensive care unit (NICU). Routine vaginal examinations versus routine rectal examinations to assess labour progress (one study, 307 women and babies) Study in Ireland involving women in labour at term. We assessed the certainty of the evidence as very low. Compared with routine rectal examinations, routine vaginal examinations may have little or no effect on: augmentation of labour (risk ratio (RR) 1.03, 95% CI 0.63 to 1.68; one study, 307 women); and spontaneous vaginal birth (RR 0.98, 95% CI 0.90 to 1.06; one study, 307 women). We found insufficient data to fully assess: neonatal infections (RR 0.33, 95% CI 0.01 to 8.07; one study, 307 babies); and admission to NICU (RR 1.32, 95% CI 0.47 to 3.73; one study, 307 babies). The study did not assess our other primary outcomes: positive birth experience; chorioamnionitis; maternal pain. Routine four-hourly vaginal examinations versus routine two-hourly examinations (one study, 150 women and babies) UK study involving primiparous women in labour at term. We assessed the certainty of the evidence as very low. Compared with routine two-hourly vaginal examinations, routine four-hourly vaginal examinations may have little or no effect, with data compatible with both benefit and harm, on: augmentation of labour (RR 0.97, 95% CI 0.60 to 1.57; one study, 109 women); and spontaneous vaginal birth (RR 1.02, 95% CI 0.83 to 1.26; one study, 150 women). The study did not assess our other primary outcomes: positive birth experience; chorioamnionitis; neonatal infection; admission to NICU; maternal pain. Routine vaginal examinations versus vaginal examinations as indicated (one study, 204 women and babies)  Study in Malaysia involving primiparous women being induced at term. We assessed the certainty of the evidence as low. Compared with vaginal examinations as indicated, routine four-hourly vaginal examinations may result in more women having their labour augmented (RR 2.55, 95% CI 1.03 to 6.31; one study, 204 women). There may be little or no effect on: • spontaneous vaginal birth (RR 1.08, 95% CI 0.73 to 1.59; one study, 204 women); • chorioamnionitis (RR 3.06, 95% CI 0.13 to 74.21; one study, 204 women); • neonatal infection (RR 4.08, 95% CI 0.46 to 35.87; one study, 204 babies); • admission to NICU (RR 2.04, 95% CI 0.63 to 6.56; one study, 204 babies). The study did not assess our other primary outcomes of positive birth experience or maternal pain.

AUTHORS' CONCLUSIONS

Based on these findings, we cannot be certain which method is most effective or acceptable for assessing labour progress. Further large-scale RCT trials are required. These should include essential clinical and experiential outcomes. This may be facilitated through the development of a tool to measure positive birth experiences. Data from qualitative studies are also needed to fully assess whether methods to evaluate labour progress meet women's needs for a safe and positive labour and birth, and if not, to develop an approach that does.

Ultrasound vs routine care before instrumental vaginal delivery: A systematic review and meta-analysis

INTRODUCTION

The objective was to report the role of intrapartum ultrasound examination in affecting maternal and perinatal outcome in women undergoing instrumental vaginal delivery.

MATERIAL AND METHODS

MEDLINE, Embase, CINAHL, Google Scholar and ClinicalTrial.gov databases were searched. Inclusion criteria were randomized controlled trials comparing ultrasound assessment of fetal head position vs routine standard care (digital examination) before instrumental vaginal delivery (either vacuum or forceps). The primary outcome was failed instrumental delivery extraction followed by cesarean section. Secondary outcomes were postpartum hemorrhage, 3rd or 4th degree perineal lacerations, episiotomy, prolonged hospital stay, Apgar score<7 at 5 min, umbilical artery pH <7.0 and base excess greater than -12 mEq, admission to neonatal intensive care unit (NICU), shoulder dystocia, birth trauma, a composite score of adverse maternal and neonatal outcome and incorrect diagnosis of fetal head position. Risk of bias was assessed using the Revised Cochrane risk-of-bias tool for randomized trials (RoB-2). The quality of evidence and strength of recommendations were assessed using the Grading of Recommendations Assessment Development and Evaluation (GRADE) methodology. Head-to-head meta-analyses using a random-effect model were used to analyze the data and results are reported as relative risk with their 95% confidence intervals.

RESULTS

Five studies were included (1463 women). There was no difference in the maternal, pregnancy or labor characteristics between the two groups. An ultrasound assessment prior to instrumental vaginal delivery did not affect the cesarean section rate compared with standard care (p = 0.805). Likewise, the risk of composite adverse maternal outcome (p = 0.428), perineal lacerations (p = 0.800), postpartum hemorrhage (p = 0.303), shoulder dystocia (p = 0.862) and prolonged stay in hospital (p = 0.059) were not different between the two groups. Composite adverse neonatal outcome was not different between the women undergoing and those not undergoing ultrasound assessment prior to instrumental delivery (p = 0.400). Likewise, there was no increased risk with abnormal Apgar score (p = 0.882), umbilical artery pH < 7.2 (p = 0.713), base excess greater than -12 (p = 0.742), admission to NICU (p = 0.879) or birth trauma (p = 0.968). The risk of having an incorrect diagnosis of fetal head position was lower when ultrasound was performed before instrumental delivery, with a relative risk of 0.16 (95% confidence interval 0.1-0.3; I² :77%, p < 0.001).

CONCLUSIONS

Although ultrasound examination was associated with a lower rate of incorrect diagnoses of fetal head position and station, this did not translate to any improvement of maternal or neonatal outcomes.

Intrapartum ultrasound and the choice between assisted vaginal and cesarean delivery

Inaccurate assessment of the fetal head position and station might increase the risk for difficult or failed assisted vaginal delivery. Compared with digital vaginal examination, an ultrasound examination is objective and more accurate. The International Society of Ultrasound in Obstetrics and Gynecology has issued practical guidelines on intrapartum ultrasound in 2018 and recommended that an ultrasound assessment should be conducted when there is suspected delay or arrest of the first or second stage of labor or before considering assisted vaginal delivery. Fetal head position is assessed transabdominally by identifying the fetal occiput, orbit, or midline cerebral echo. Studies have shown that ultrasound assessment improved the correct diagnosis of fetal head position and accuracy of instrument placement, however, it did not reduce morbidity. Studies on ultrasound assessment of asynclitism are limited but show promising results. Fetal head station is assessed transperineally in the midsagittal or axial plane. Of the various ultrasound parameters, angle of progression and head-perineum distance are the most widely studied and found to be highly correlated with the clinical fetal head station. An angle of progression of 120° correlates with a clinical head station of 0 and is an important landmark for engagement of successful vaginal delivery, whereas an angle of progression of 145° correlates with a clinical head station of ≥+2 and has been associated with successful assisted vaginal delivery. In contrast, a head perineum distance of ≥40 mm has been associated with an increased risk for difficult assisted vaginal delivery. A "head-up" direction of descent assessed transperineally in sagittal plane is also a favorable factor for successful vaginal delivery. Current evidence seems to suggest that a prediction model with >1 sonographic parameter performed better than a model that only used 1 parameter. We suggest that an algorithm model incorporating both clinical and sonographic parameters would be useful in guiding clinicians on their decision for assisted vaginal delivery.