Intrapartum ultrasound

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.

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.

Intrapartum ultrasound for the management of the active pushing phase

The anxiety and anticipation that accompany pregnancy, labor, and delivery may be relieved by education, providing knowledge regarding the physiological process of childbirth. Intrapartum ultrasound is an available, simple, intuitive, real-time tool that enables visualization of the fetal head within the birth canal. Both the attending staff and expectant parent can assess its movements and descent in response to the pushing efforts during the active pushing phase. This review described the potential obstetrical and psychological advantages of intrapartum ultrasound in managing the active pushing phase.

Head progression distance during the first stage of labor as a predictor for delivery outcome

Objectives: To assess if measurement of the head progression distance (PD) during the first stage of labor in nulliparous women can predict the delivery method.Methods: A prospective study was conducted on consecutive nulliparous women beyond 37 week's gestation during the first stage of labor. Transperineal ultrasound was performed to assess the PD. Analysis was performed on the relationships between PD during rest and during voluntary pushing and the fetal and maternal characteristics, delivery mode, and immediate postnatal outcomes.Results: Eighty seven suitable nulliparous women were suitable for analysis. PD was found to be significantly longer in women who delivered vaginally (VD) compared to those who underwent a cesarean section (CS) for obstructed labor: PD at rest was 2.51 ± 1.71 cm in women who delivered vaginally compared to 1.48 ± 1.9 cm in women who delivered by CS (p = .01). The PD during pushing was 3.43 ± 1.8 cm for a VD compared to 1.5 ± 2.1 cm for CS (p = .015). Logistic regression and receiver-operating characteristics curve analysis demonstrated a moderate predictive value of PD with respect to the mode of delivery (area under the curve was 0.67 during both resting and pushing period).Conclusion: PD measurements during the first stage of labor among nulliparous women differ significantly both in rest and during pushing between patients who delivered vaginally compared to CS and can therefore assist in predicting the mode of delivery.

Intrapartum ultrasound assessment of cervical dilatation and its value in detecting active labor

Introduction

We aimed to examine the agreement between ultrasound and digital vaginal examination in assessing cervical dilatation in an African population and to assess the value of ultrasound in detecting active labor.

Method

A cross-sectional study was conducted in a teaching hospital in Ghana between April and September of 2016. Anterior–posterior and transverse diameters of cervical dilatation were measured with ultrasound and the mean value was compared with digital vaginal examination in 195 women in labor. Agreement between methods was examined with correlation coefficients and with Bland–Altman plots. Active labor was defined when cervix was dilated ≥ 4 cm with vaginal examinations. ROC curve analysis was conducted on the diagnostic performance of ultrasound in detecting active labor.

Results

Data were analyzed in 175 out of 195 (90%) cases where ultrasound could clearly visualize the cervix. The remaining 20 cases were all determined by digital vaginal examination as advanced cervical dilatation (≥ 8 cm), advanced head station (≥ + 2), and with ruptured membranes. The Pearson correlation coefficient (r) was 0.78 (95% CI 0.72–0.83) and the intra-class correlation coefficient was 0.76 (95% CI 0.69–0.81). Bland–Altman analysis obtained a mean difference of − 0.03 cm (95% CI − 0.18 to 0.12) with zero included in the CI intervals, indicating no significant difference between methods. Limits of agreement were from − 2.01 to 1.95 cm. Ultrasound predicted active labor with 0.87 (95% CI 0.75–0.99) as the area under the ROC curve.

Conclusion

Ultrasound measurements showed good agreement with digital vaginal examinations in assessing cervical dilatation during labor and ultrasound may be used to detect active labor.

Pre-induction translabial ultrasound measurements in predicting mode of delivery compared to bishop score: a cross-sectional study

Background

By increased concerns about the accuracy of the traditional methods to predict outcomes after induction of labor, developing new standards has a great clinical importance. Here, we compared the predictive value of translabial ultrasound measurements with Bishop Score to determine the suitability of induction of labor.

Methods

A homogenous population of primigravid women was recruited. Induction of labor was performed with low-dose infusion of oxytocin. Translabial ultrasound and assessment of Bishop Score were performed by two different obstetricians. Receiver–operating characteristics curves were obtained to measure area under curve and subsequently, test sensitivity of each method.

Results

One hundred women entered the investigation. Maternal body mass index was significantly higher among candidates of Cesarean section (P: 0.02). Maternal age and fetus weight, gender and occiput position were not determinants of outcomes of induction of labor. Cervical length and fetal head-pubis symphysis distance measured by translabial ultrasound had a test sensitivity of 90 and 88 %, respectively which were slightly higher than sensitivity of Bishop score (84 %).

Conclusion

This study demonstrates that translabial measurements can be a suitable alternative method to monitor labor progress with an admissible predictive value compared with Bishop Score. It is a non-invasive method which provides valuable objective measurements and can be better accepted by women when considering the painful process which is required in evaluating Bishop Score.

[Accuracy of ultrasound estimated fetal weight performed by residents at delivery day]

Ultrasound fetal weight estimation (EFW) has become a routine practice in obstetrics with a major impact on obstetrical management.

OBJECTIVES

To evaluate the accuracy of sonographic fetal weight estimations performed by residents in obstetrics at the delivery day and to search parameters influencing this exam.

METHODS

A prospective study performed in 299 patients at 37 weeks of gestation or more, during their delivery day. Ultrasound fetal weight estimations were performed by residents and compared to birth weights (BW). The estimated fetal weight (EFW) was calculated using the formula of Hadlock: Log10 EPF=1,335+0.0316 BIP+0,0457 PA+0,1623 LF-0,0034 PA LF.

RESULTS

Mean absolute difference between EFW and BW was 200g [100-450]. Mean absolute percentage error was 5.71 % [2.7-11.37]. The proportion of the EFW within 10 % of BW was 69.6 %. There was a good correlation between EFW and BW (R=0.79). Obesity and fetal macrosomia had negatively influenced ultrasound performance. For the diagnosis of macrosomia, ultrasound has a sensibility of 38 % and a specificity of 99.59 %.

CONCLUSION

Ultrasound fetal weight estimations performed by residents in the delivery room were as accurate as those performed by experimented sonographers. Thus, the predictive performance remains limited with a low sensitivity in the diagnosis of macrosomia.

Impact of fetal pulse oximetry and ST analysis surveillance withdrawal on rates of obstetric surgery and frequency of low birth umbilical artery pH: a cause of rising caesarean rates?

A retrospective observational study on a sample of 13,413 deliveries analysed the effect of a withdrawal of the CTG additional diagnostic methods of fetal hypoxia (fetal pulse oximetry and ST analysis of the fetal ECG) on operative delivery rates and frequency of the umbilical arterial pH < 7.15. Following the withdrawal, obstetricians are more likely to perform caesarean sections for fetal hypoxia (OR 2.23, 95% CI 1.94-2.55, p < 0.0001) and labour dystocia (OR 1.45, 95% CI 1.18-1.77, p = 0.0003), which increases the overall caesarean rate (OR 1.49, 95% CI 1.38-1.61, p < 0.0001), although decreases the incidence of birth umbilical arterial pH < 7.15 (OR 0.43, 95% CI 0.22-0.85, p = 0.015). This also leads to the significant decline in overall frequency of instrumental vaginal deliveries (OR 0.58, 95% CI 0.48-0.71). In order to decrease the overall caesarean rate, obstetricians need to be supported by more accurate and possibly automated diagnostic tools for intrapartum fetal hypoxia.

Head progression distance in prolonged second stage of labor: relationship with mode of delivery and fetal head station

OBJECTIVE

To evaluate the clinical significance of fetal head progression distance (HPD), measured by transperineal ultrasound, during prolonged second stage of labor.

METHODS

In this prospective study, a single operator, who was blinded to the results of the digital examination, assessed using transperineal ultrasound women at ≥ 37 weeks of gestation with failure to progress in the second stage of labor. Patients had an empty urinary bladder and the examination was performed during maternal pushing. HPD was defined as the length of the line perpendicular to the infrapubic line that would connect it to the lowest part of the fetal bony skull. We analyzed associations between HPD and digital examination of fetal head station, fetomaternal characteristics, mode of delivery and perinatal outcome.

RESULTS

Sixty-five patients in prolonged second stage of labor participated in the study. The overall mean HPD was 6.50 (± 1.35; 95% CI, 6.16-6.83) cm. No correlation was found between HPD and head position or mode of delivery, but HPD was positively correlated with fetal head station and neonatal head circumference measured after delivery. Logistic regression and receiver-operating characteristics curve analysis demonstrated no significant predictive value of HPD with respect to mode of delivery.

CONCLUSION

Although HPD in prolonged second stage of labor could not predict mode of delivery, it may have a role as an ancillary tool for fetal head station assessment.

Simple two-dimensional ultrasound technique to assess intrapartum cervical dilatation: a pilot study

OBJECTIVES

To describe a two-dimensional (2D) ultrasound technique to measure cervical dilatation in labor, and to compare ultrasound with digital measurements.

METHODS

2D transperineal ultrasound was performed in 21 nulliparous women in labor with a singleton fetus in cephalic presentation and cervical dilatation measured before or after a digital vaginal examination. The absolute difference was calculated and Bland-Altman analysis was used to assess the mean difference between digital vaginal examination and ultrasound examination of cervical dilatation. Pearson analysis was used to determine the correlation between digital and ultrasound measurements. Intraclass correlation coefficients (ICCs) with 95% CI were used to evaluate the reliability of the two methods.

RESULTS

Satisfactory quality images of the cervix were obtained in 19 of 21 cases. There was positive correlation between 2D ultrasound measurement of cervical dilatation and digital vaginal examination (Pearson coefficient r = 0.821, n = 19, P < 0.001). Bland-Altman analysis showed a mean difference between digital and ultrasound measurements of 0.08 cm (95% limits of agreement: -1.83 to 2.00) and the mean absolute difference was 1.24 cm. The ICC between the two methods was 0.81 (95% CI, 0.58-0.92).

CONCLUSIONS

Assessment and measurement of cervical dilatation by 2D transperineal ultrasound is feasible, with close agreement shown between the technique and digital vaginal examination. The technique that we describe could represent an important component of a 'sonopartogram' for ultrasound assessment of labor progress.

Relationship between fetal head station established using an open magnetic resonance imaging scanner and the angle of progression determined by transperineal ultrasound

OBJECTIVE

We investigated the correlation between the angle of progression measured by transperineal ultrasound and fetal head station measured by open magnetic resonance imaging (MRI), the gold standard, in pregnant women at full term.

METHODS

Thirty-one pregnant women at full term with a fetus in the occipitoanterior position were enrolled. First, the distance between the leading part of the skull and the interspinal plane was obtained using an open MRI system with the patient in a supine position. Immediately after MRI, the angle of progression was obtained by transperineal ultrasound without changing the woman's posture.

RESULTS

There was a significant correlation between the angle of progression determined by transperineal sonography and the distance between the presenting fetal part and the level of the maternal ischial spines (y = - 0.51x + 60.8, r(2) = 0.38, P < 0.001). None of the fetal heads was engaged at the time of MRI and ultrasound examinations.

CONCLUSIONS

The present study demonstrated a predictable relationship between the angle of progression obtained by transperineal ultrasound and the traditional scale used to quantify fetal head descent. Based on our results, station 0 would correspond to a 120° angle of progression. However, this correlation is based on statistical assumptions only and has to be proven in future studies.

Measurement of fetal head descent using the 'angle of progression' on transperineal ultrasound imaging is reliable regardless of fetal head station or ultrasound expertise

OBJECTIVES

To assess whether ultrasound experience or fetal head station affects the reliability of measurement of fetal head descent using the angle of progression on intrapartum ultrasound images obtained by a single experienced operator, and to determine reliability of measurements when images were acquired by different operators with variable ultrasound experience.

METHODS

One experienced obstetrician performed 44 transperineal ultrasound examinations of women at term and in prolonged second stage of labor with the fetus in the occipitoanterior position. Three midwives without ultrasound experience, three obstetricians with < 5 years' experience and three obstetricians with > 10 years' experience measured fetal head descent based on the angle of progression in the images obtained. The angle of progression was measured by two obstetricians in independent ultrasound examinations of 24 laboring women at term with the fetus in the cephalic position to allow assessment of the reliability of image acquisition. Intraclass correlation coefficients (ICCs) with 95% confidence interval (CI) were used to evaluate interobserver reliability and Bland-Altman analysis was used to assess interobserver agreement.

RESULTS

In total, 444 measurements were performed and compared. Interobserver reliability with respect to offline image analysis was substantial (overall ICC, 0.72; 95% CI, 0.63-0.81). ICCs were 0.82 (95% CI, 0.70-0.89), 0.81 (95% CI, 0.71-0.88) and 0.61 (95% CI, 0.43-074) for observers with > 10 years', < 5 years' and no ultrasound experience, respectively. There were no significant differences between ICCs among observer groups according to ultrasound experience. Fetal head station did not affect reliability. Bland-Altman analysis indicated reasonable agreement between measurements obtained by two different operators with > 10 years' and < 5 years' ultrasound experience (bias, -1.09 degrees ; 95% limits of agreement, -8.76 to 6.58). The reliability of measurement of the angle of progression following separate image acquisition by two experienced operators was similar to the reliability of offline image analysis (ICC, 0.86; 95% CI, 0.70-0.93).

CONCLUSIONS

Measurement of the angle of progression on transperineal ultrasound imaging is reliable regardless of fetal head station or the clinician's level of ultrasound experience.

Intrapartum measurement of cervical dilatation using translabial 3-dimensional ultrasonography: correlation with digital examination and interobserver and intraobserver agreement assessment

OBJECTIVE

The purpose of this study was to determine the accuracy and reproducibility of intrapartum translabial 3-dimensional (3D) ultrasonographic measurements of cervical dilatation during labor.

METHODS

A prospective observational study was conducted. Three-dimensional ultrasonographic volume data sets from 52 patients were collected during labor and stored. Later, all volumes were randomly reviewed twice offline by 2 examiners blinded to previous clinical and ultrasonographic measurements. The correlation with delivery room personnel digital vaginal examinations and interobserver and intraobserver agreement were determined.

RESULTS

Twenty-four patients were examined during the latent phase (0- to 4-cm cervical dilatation), and 28 patients were examined during the active phase (5- to 10-cm cervical dilatation). Translabial 3D ultrasonographic measurements of the cervical mean and maximal diameters and inner cervical area showed a positive correlation with digital vaginal examinations (r(2) = 0.609, 0.587, and 0.469, respectively; all P < .001). The interobserver mean differences +/- SD between paired measurements for the mean and maximal cervical dilatation and inner cervical area were 0.11 +/- 0.49 cm, 0.12 +/- 0.48 cm, and -0.22 +/- 5.69 cm(2), and the intraclass correlation coefficients (ICCs) were 0.82, 0.85, and 0.87. The intraobserver mean differences between paired measurements of the mean and maximal cervical dilatation and inner cervical area were 0.002 +/- 1.15 cm, 0.02 +/- 1.4 cm, and -0.41 +/- 1.15 cm(2), and the ICCs were 0.85, 0.79, and 0.75.

CONCLUSIONS

Assessment of cervical dilatation using 3D ultrasonography during labor is feasible and reproducible.

Diagnosis of station and rotation of the fetal head in the second stage of labor with intrapartum translabial ultrasound

OBJECTIVE

To investigate the ability of intrapartum translabial sonography to diagnose fetal station in the second stage of labor.

METHODS

Patients with uncomplicated pregnancies at term gestation with fetuses in vertex presentation in the second stage of labor underwent serial translabial sonography and digital examinations. In a sagittal section of the maternal pelvis, the direction of the head was noted and categorized as downward, horizontal or upward. By rotating the transducer in the transverse plane the cerebral midline echo was also visualized and the rotation of the head was noted. Clinical and ultrasound data were compared using Somer's d-test.

RESULTS

Sixty patients underwent a total of 168 clinical and sonographic examinations. When on the sonogram the fetal head was directed downward, the station assessed clinically was most frequently <or= + 1 cm from the ischial spines (44/57 (77.2%) cases); when the direction was horizontal, the station was most frequently <or= + 2 cm (53/59 (89.8%) cases); when the fetal head was directed upward, the station was usually >or= + 3 cm (46/52 (88.5%) cases). Failure to visualize the cerebral midline or a rotation >or= 45 degrees were associated with a station of + 2 cm or less in 98/103 (95.1%) examinations. Conversely, a rotation of < 45 degrees was associated with a station of + 3 cm or more in 45/65 (69.2%) examinations. All comparisons between clinical and sonographic findings demonstrated a statistically significant relationship (P < 0.0001). The probability of a station + 3 cm or more was particularly high when an upward direction of the head was seen in combination with a rotation of < 45 degrees (40/42 (95.2%) examinations). The interobserver variability (Cohen's kappa 0.795 and 0.727 for station and rotation, respectively; P < 0.001) and intraobserver variability (0.845 for both station and rotation, P < 0.001) suggested good reproducibility of the method.

CONCLUSIONS

Translabial sonography allows a diagnosis of fetal station with an accuracy comparable to that of digital examination and may provide useful information for diagnosing obstructed labor in the second stage as well as assisting in the choice of instrumental delivery.

Transperineal ultrasound imaging in prolonged second stage of labor with occipitoanterior presenting fetuses: how well does the 'angle of progression' predict the mode of delivery?

OBJECTIVES

To compare the angle of progression on transperineal ultrasound imaging between different modes of delivery in prolonged second stage of labor with occipitoanterior fetal position.

METHODS

We prospectively evaluated 41 women at term (>or= 37 weeks) with failure to progress in the second stage of labor. Only cases with occipitoanterior fetal position were included in the final analysis. These cases were classified into three groups: Cesarean section for failure to progress, vacuum extraction for failure to progress, and spontaneous delivery following prolonged second stage of labor. Transperineal ultrasound examination was performed just before digital examination and subsequent delivery. The angle between a line placed through the midline of the pubic symphysis and a line running from the inferior apex of the symphysis tangentially to the fetal skull (the so-called 'angle of progression') was measured offline by an observer blinded to the mode of delivery.

RESULTS

There were 26 cases with occipitoanterior fetal position (Cesarean section, n = 5; vacuum extraction, n = 16; spontaneous delivery, n = 5). Logistic regression analysis showed a strong relationship between the angle of progression and the need for Cesarean delivery (R(2) measure of fit = 55%, likelihood ratio chi-square P < 0.0001). When the angle of progression was 120 degrees , the fitted probability of either an easy and successful vacuum extraction or spontaneous vaginal delivery was 90%.

CONCLUSIONS

This is the first report to document a strong relationship between an objective ultrasound marker (angle of progression) and the mode of delivery following prolonged second stage of labor with occipitoanterior fetal position. A predictive model using this parameter would allow better decision making regarding operative delivery for obstructed labor.

Abdominal and pelvic ultrasound findings within 24 hours following uneventful Cesarean section

OBJECTIVES

To describe prospectively the normal abdominal and pelvic ultrasound features within 24 h following uneventful Cesarean section.

METHODS

Transabdominal ultrasound examination was performed between 1 and 3 h, and again at 24 h, following lower-segment Cesarean section (LSCS). The myometrium, endometrium, and amount and distribution of free peritoneal fluid were studied in 30 women with singleton pregnancies who underwent LSCS delivery.

RESULTS

Examinations were performed easily in all cases except one who was morbidly obese (body mass index > 40 kg/m(2)). At 1-3 h after delivery, mean +/- SD endometrial thickness was 13 +/- 2 mm. Mean uterine length, from the fundus to the cervical external os, was 160 +/- 15 mm. Measurement of uterine length in the mid-sagittal plane of the pelvis was impossible in eight cases (27%) owing to pain. No abnormal intrauterine findings were observed. Mean uterine width was 110 +/- 10 mm. Mean distance between the sacral promontory and uterine fundus was 104 +/- 11 mm. Mean thicknesses of the anterior and posterior walls of the uterus were 40 +/- 5 mm and 39 +/- 7 mm, respectively. No fluid was seen in Morrison's or Douglas' pouches. There was a consistent and significant reduction between the measurements performed at 1-3 h and those at 24 h after LSCS, except for the distance between the fundus and external os.

CONCLUSIONS

Ultrasound examination is feasible after Cesarean section. Images are obtained easily, even when scanning through the scar. In normal pregnancies, there is no fluid in the abdomen or pelvis. These results could help clinicians in the decision-making process in cases of early postpartum hemorrhage or hemodynamic instability following LSCS.

Ultrasound assessment of fetal head-perineum distance before induction of labor

OBJECTIVES

To evaluate fetal head-perineum distance measured by ultrasound imaging as a predictive factor for induction of labor, and to compare this distance with maternal factors, the Bishop score and ultrasound measurements of cervical length, cervical angle and occiput position.

METHODS

The study included 275 women admitted for induction of labor. The fetal head-perineum distance was measured by transperineal ultrasound imaging as the shortest distance from the outer bony limit of the fetal skull to the skin surface of the perineum. Cervical length and angle was measured by transvaginal ultrasound examination, and fetal head position was assessed by transabdominal ultrasound imaging. The Bishop score was assessed without knowledge of ultrasound measurements. Receiver-operating characteristics (ROC) curves were used for evaluation of the probability of a successful vaginal delivery. The time from induction to delivery was tested using Cox regression analysis with ultrasound measurements, parity and body mass index (BMI) as possible predictive factors.

RESULTS

Areas under the ROC curve for prediction of vaginal delivery were 62% (95% CI, 52-71%) for fetal head-perineum distance (P = 0.03), 61% (95% CI, 51-71%) for cervical length (P = 0.03), 63% (95% CI, 52-74%) for cervical angle (P = 0.02), 61% (95% CI, 52-70%) for Bishop score (P = 0.03) and 60% (95% CI, 51-69%) for BMI (P = 0.05). The Cesarean delivery rate was 22% among nulliparous and 5% among parous women (P < 0.01). Parity, fetal head-perineum distance, cervical length and cervical angle were contributing factors predicting vaginal delivery within 24 h in a Cox regression model. Occiput posterior position had no significant predictive value.

CONCLUSIONS

Fetal head-perineum distance measured by transperineal ultrasound examination can predict vaginal delivery after induction of labor, with a predictive value similar to that of ultrasonographically measured cervical length and the Bishop score. However, we judge none of these methods used alone to be good enough in a clinical setting.