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?

Intrapartum ultrasound: A useful method for evaluating labor progress and predicting operative vaginal delivery

The last step of a successful pregnancy is the safe delivery of the fetus. An important question is if the delivery should vaginal or operative. In addition to the use of conventional antenatal ultrasound, the use of intrapartum ultrasound to evaluate fetal head station, position, cervical ripening, and placental separation is promising. This review evaluates and summarizes the usefulness of intrapartum ultrasound for the evaluation of labor progress and predicting successful operative vaginal delivery.

Successful induction of labor: prediction by preinduction cervical length, angle of progression and cervical elastography

OBJECTIVE

To examine the potential value of preinduction cervical length, cervical elastography and angle of progression (AOP) in prediction of successful vaginal delivery and induction-to-delivery interval.

METHODS

This was a prospective study in 99 women with singleton pregnancy undergoing preinduction ultrasound assessment at 35-42 weeks' gestation. Cervical length, elastographic score at the internal os and AOP were determined. Regression analysis was used to assess the relationship between cervical length and both AOP and elastographic score. Logistic regression analysis was used to determine which of the maternal characteristics (cervical length, AOP, elastographic score) were significant predictors of vaginal delivery and induction-to-delivery interval.

RESULTS

Vaginal delivery occurred in 66 (66.7%) cases and Cesarean delivery was performed in 33 (33.3%) cases. There were significant correlations between cervical length and both AOP (r = - 0.319) and elastographic score (r = 0.368). Significant independent prediction of vaginal delivery and induction-to-delivery interval was provided by nulliparity and cervical length, with no additional significant contribution from electrographic score or AOP.

CONCLUSIONS

In women undergoing induction of labor, AOP and elastographic score at the internal os are unlikely to be useful in prediction of vaginal delivery and induction-to-delivery interval.

Overweight and Obesity before, during and after Pregnancy: Part 2: Evidence-based Risk Factors and Interventions

Overweight and obesity have become a global health problem. Obesity and excessive weight gain during pregnancy have a serious impact on maternal, fetal and neonatal outcomes. Pre-conceptional obesity and excessive weight gain during pregnancy are associated with weight gain in women following childbirth leading to associated risks such as metabolic syndrome, cardiovascular disease and diabetes. Long-term risks for the offspring are an increased risk for early cardiovascular events, metabolic syndrome and decreased life expectancy as adults. German health care has not yet adequately responded to this development. There are no clinical guidelines for obesity before, during or after pregnancy, there are no concerted actions amongst midwives, obstetricians, health advisors, politicians and the media. Research projects on effective interventions are lacking although health care concepts would be urgently needed to reduce future metabolic and cardiovascular risks for women and children as well as to minimize the associated costs for the society.

Sonographic pattern of fetal head descent: relationship with duration of active second stage of labor and occiput position at delivery

OBJECTIVES

The objectives of this study were firstly to assess the longitudinal changes of various sonographic parameters of fetal head progression in relation to length of active second stage of labor, and secondly to compare ultrasound findings obtained longitudinally among fetuses with persistent occiput posterior (OP) vs those with persistent occiput anterior (OA) position.

METHODS

From a series of nulliparous low-risk women at term attending the labor ward of our university hospital, transperineal ultrasound volumes were prospectively acquired at the beginning of the active second stage (T1) and at 40-min intervals thereafter until delivery (T2, T3). Sonographic parameters were derived from offline analysis of each volume, including the angle of progression (AoP), progression distance (PD), head-symphysis distance (HSD), head direction (HD) and midline angle. These parameters were compared between patients who delivered within 60 min from the beginning of the active second stage of labor (early delivery) and those who remained undelivered by that time (late delivery). Fetal head position was determined from stored digital images of transabdominal examinations performed at the beginning of the active second stage. Comparison was performed between fetuses with OA and those with persistent OP position at delivery.

RESULTS

Spontaneous vaginal delivery was achieved in 58 (81.7%) cases, whereas vacuum extraction and Cesarean section were performed in eight (11.3%) and five (7.0%) cases, respectively. Delivery was achieved within 60 min from the beginning of the active second stage in 44 (62.0%) patients. In the early vs late delivery groups, measurements of AoP, HSD and PD at T1 were significantly different (AoP, 143.9 ± 20.5° vs 125.3 ± 15.0°, P < 0.001; HSD, 14.8 ± 4.5 mm vs 20.9 ± 5.8 mm, P < 0.001; PD, 44.0 ± 14.1 vs 35.0 ± 13.1 mm, P = 0.008). On logistic regression analysis of data obtained at T1, maternal body mass index, oxytocin administration, neonatal birth weight and HSD appeared to predict independently duration of the active second stage. Among fetuses delivering in the OP position (n = 10, 13.5%), Cesarean delivery was significantly more common than in those delivering in the OA position (n = 5 (50.0%) vs n = 2 (3.1%), P = 0.001). Women with persistent OP position compared with OA showed a significantly different AoP at T1 (122 ± 17° vs 138 ± 20°, P = 0.016), HD and HSD at T1 (HD, 112 ± 17 mm vs 86 ± 19 mm, P < 0.001; HSD, 16.5 ± 5.4 mm vs 22.8 ± 6.6 mm, P = 0.008) and at T2 (HD, 120 ± 16 vs 82 ± 27 mm, P = 0.008; HSD, 12.6 ± 3.4 mm vs 18.5 ± 5.4 mm, P = 0.038).

CONCLUSIONS

AoP, PD and HSD are significantly different between patients undergoing delivery before or after 60 min from the beginning of the active second stage of labor. Ultrasound parameters are among the significant predictors of duration of the active second stage. Moreover, in fetuses persisting in the OP position vs those delivering in the OA position, fetal head progression seems to differ at early phases of the active second stage.

Use of intrapartum ultrasound in the prediction of complicated operative forceps delivery of fetuses in non-occiput posterior position

OBJECTIVE

To evaluate the hypothesis that intrapartum ultrasound (ITU) measurements, including the angle of progression (AOP), progression distance (PD) and head direction (HD), can predict complicated forceps delivery in non-occiput posterior deliveries.

METHODS

In this prospective observational study, a single operator performed ITU on 30 patients with an indication for operative forceps delivery. Managing obstetricians were blinded to the results. ITU was performed just before blade application, between contractions and concurrently with contractions and active pushing. Forceps delivery was classified as complicated when one or more of the following situations occurred: three or more tractions; a subjective impression of a difficult or failed application; a third-degree or higher perineal tear; significant bleeding during the episiotomy repair; major tear; significant traumatic neonatal lesion.

RESULTS

Twenty-one forceps deliveries were classified as uncomplicated and nine were complicated. The strongest predictor of a complicated forceps delivery, calculated using the area under the receiver-operating characteristics curve (AUC), was the AOP between contractions (AOP1) (AUC = 98.9%). The best cut-off for predicting a difficult forceps delivery was an AOP1 of 138° (sensitivity = 85.7%, specificity = 100%). The best predictive model included both the AOP1 and the HD during a contraction with active pushing (HD2).

CONCLUSION

The sonographic parameters AOP and HD can be used to predict complicated operative forceps delivery in fetuses in non-occiput posterior position.

Sonographic prediction of vaginal delivery in prolonged labor: a two-center study

OBJECTIVE

To investigate whether head-perineum distance (HPD) measured by transperineal ultrasound is predictive of vaginal delivery and time remaining in labor in nulliparous women with prolonged first stage of labor and to compare the predictive value with that of angle of progression (AoP).

METHODS

This was a prospective observational study at Stavanger University Hospital, Norway and Addenbrooke's Hospital, Cambridge, UK from January 2012 to April 2013, of nulliparous women with singleton pregnancies with cephalic presentation at term with prolonged first stage of labor. We used transperineal ultrasound to measure HPD (shortest distance between the outer bony limit of the fetal skull and the perineum) and AoP (angle between a line through the long axis of the symphysis and the tangent to the fetal head) and transabdominal ultrasound to classify fetal head position. The main outcomes were vaginal delivery and time remaining in labor.

RESULTS

Of 150 women enrolled, 39 underwent delivery by Cesarean section. The area under the receiver-operating characteristics curve for the prediction of vaginal delivery was 81% (95% CI, 73-89%) using HPD as the test variable and 72% (95% CI, 63-82%) using AoP. HPD was ≤ 40 mm in 84 (56%) women, of whom 77 (92%; 95% CI, 84-96%) delivered vaginally. HPD was > 40 mm in the other 66 (44%) women, of whom 34 (52%; 95% CI, 40-63%) delivered vaginally. AoP was ≥ 110° in 84 of the 145 (58%) in whom this was available and, of these, 74 (88%; 95% CI, 79-93%) delivered vaginally. AoP was < 110° in the other 61 (42%) women, of whom 35 (57%; 95% CI, 45-69%) delivered vaginally. Multivariable logistic regression analysis showed that HPD ≤ 40 mm (odds ratio (OR), 4.92; 95% CI, 1.54-15.80), AoP ≥ 110° (OR, 3.11; 95% CI, 1.01-9.56), non-occiput posterior position (OR, 3.36; 95% CI, 1.24-9.12) and spontaneous onset of labor (OR, 4.44; 95% CI, 1.42-13.89) were independent predictors for vaginal delivery. Both ultrasound methods were predictive for the time remaining in labor.

CONCLUSION

Transperineal ultrasound measurement of HPD and AoP provide important information about the likelihood of vaginal delivery and the time remaining in labor in nulliparous women with prolonged labor.

The sonopartogram: a novel method for recording progress of labor by ultrasound

OBJECTIVES

Progress of labor has hitherto been assessed by digital vaginal examination (VE). We introduce the concept of a non-intrusive ultrasound (US)-based assessment of labor progress (the 'sonopartogram') and investigate its feasibility for assessing cervical dilatation and fetal head descent and rotation.

METHODS

This was a prospective study performed in 20 women in the first stage of labor in two European maternity units. Almost simultaneous assessment of cervical dilatation and fetal head descent and rotation were made by US and digital VE.

RESULTS

The total number of paired US and digital VE assessments was 52, with a median of three per woman. Overall, 5% of sonopartogram parameters were not obtained compared with 18% of conventional digital VE parameters (P < 0.001). Assessment of cervical dilatation was possible in 86.5% of US examinations and 100% of digital VEs (P = 0.02), and dilatation was assessed as being greater by digital VE than by US (mean difference, 1.16 (95% limits of agreement, -0.76, 3.08) cm, r(2) = 0.68, P = 0.01). Fetal head descent was measured in all 52 cases by both methods (r(2) = 0.33, P < 0.001), but correlation between the two was only moderate. Head rotation was obtainable in 98% of US examinations and 46% of digital VEs (P < 0.001), with a mean difference of -3.9° (95% limits of agreement, -144.1°, 136.3°).

CONCLUSION

In this proof-of-concept study, the acquisition of data regarding progress of labor was more successful for the sonopartogram than the conventional partogram. The agreement between digital VE and US was good for cervical dilatation and head rotation but less so for head descent. US assessment of the progress of labor is feasible in most cases.

Intrapartum sonographic assessment of labor

Fetal head progression during labor is difficult to assess. Digital examination has been shown to be an inaccurate method. Utilizing the ultrasound technology in the delivery room can standardize the way we assess head progression. Intrapartum ultrasound is applicable, for the assessment of the progression of labor and assists the obstetrician, in decision making regarding the need for an assisted delivery. This article summarizes the latest studies regarding the usage of ultrasound in the delivery room and the measurements that are used during delivery.

Caput succedaneum thickness in prolonged second stage of labour: a clinical evaluation

BACKGROUND

Data are scarce regarding the association between the presence of caput succedaneum and the mode of delivery.

AIMS

To evaluate the presence and clinical significance of caput succedaneum thickness in prolonged second stage of labour.

MATERIALS AND METHODS

We conducted a prospective study of women, beyond 37 weeks of gestation, during prolonged second stage of labour. Transperineal ultrasound was performed to assess the caput succedaneum thickness. The relationships between caput succedaneum thickness, feto-maternal characteristics, delivery mode and immediate post-natal outcomes were analysed.

RESULTS

Fifty-eight women, of whom 47 were nulliparas, in prolonged second stage of labour, were included in the study. The caput succedaneum thickness could be measured in all cases. Overall mean thickness was 21.9 (±4.9) mm (range 14-40 mm). No significant difference or correlation was found between caput succedaneum thickness, fetal head positions, modes of delivery, duration of second stage, head circumference or neonatal outcomes.

CONCLUSIONS

Caput succedaneum is measurable in all cases at prolonged second stage using transperineal sonography. Its presence and dimensions presented in our pilot study seem to have no implication on delivery mode and neonatal outcome.

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.

Intrapartum transperineal ultrasound assessment of fetal head progression in active second stage of labor and mode of delivery

OBJECTIVE

To compare longitudinal changes in angle of progression (AoP) and midline angle (MLA) during the active second stage of labor according to the mode of delivery.

METHODS

A three-dimensional transperineal ultrasound volume was acquired in a series of nulliparous women at the beginning of the active second stage (T1) and every 20 min thereafter (T2, T3, T4, T5 and T6). Following delivery, all ultrasound volumes were analyzed and AoP and MLA were measured.

RESULTS

Among 71 women included in the study, 58 underwent spontaneous vaginal delivery (group A) and 13 underwent operative delivery (group B) (eight by vacuum extraction and five by Cesarean section). When compared with Group B, Group A had a wider AoP only at T1 (140.0 ± 20.2° vs. 122.9 ± 16.7°; P = 0.010) and T2 (149.7 ± 20.7° vs. 126.9 ± 17.5°; P = 0.006). MLA was narrower in group A only at T3 (21.2 ± 11.7° vs. 40.8 ± 27.9°; P = 0.043), T4 (18.2 ± 15.0° vs. 47.4 ± 29.6°; P = 0.020) and T5 (18.3 ± 6.0° vs. 34.7 ± 4.2°; P = 0.034). On stepwise forward multiple logistic regression analysis, both AoP and MLA were independently associated with operative delivery (OR = 0.955 and OR = 1.018, respectively).

CONCLUSION

Ultrasonographic assessment of fetal head descent in the second stage of labor may play a role in the prediction of the mode of delivery.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Fetal head-symphysis distance: a simple and reliable ultrasound index of fetal head station in labor

OBJECTIVES

To assess the reproducibility of measurement of a new sonographic index of fetal head station in labor, the fetal head-symphysis distance (HSD), using three-dimensional ultrasound, and its correlation with digital assessment of fetal head descent and with the angle of progression (AoP).

METHODS

Three-dimensional (3D) ultrasound volumes were acquired from 47 nulliparous women in active labor following assessment of fetal head station with digital examination. The HSD (the distance between the lower edge of the pubic symphysis and the nearest point of the fetal skull) was measured independently by two operators in order to evaluate intra- and interobserver reproducibility. The correlation between HSD, AoP and fetal head station was evaluated using regression analysis. Using 3D tomographic ultrasound imaging (TUI), measurements of the HSD were obtained in different parasagittal planes to evaluate the influence of inaccurate alignment of the probe with the midline of the pelvis.

RESULTS

Measurement of HSD showed high intraobserver (intraclass correlation coefficient (ICC) = 0.995; 95% CI, 0.991-0.997) and interobserver (ICC = 0.991; 95% CI, 0.984-0.995) reliability. In addition, a high correlation was demonstrated between mid-sagittal and parasagittal HSD measurements. HSD showed significant negative correlation with both fetal head station and AoP.

CONCLUSION

Fetal HSD is a simple and reliable method for the assessment of fetal head descent in labor.

Pubic arch angle in prolonged second stage of labor: clinical significance

OBJECTIVE

To evaluate the clinical significance of the pubic arch angle (PAA) measured by transperineal ultrasound during prolonged second stage of labor.

METHODS

We evaluated prospectively 62 women ≥ 37 weeks of gestation with failure to progress in the second stage of labor. Transperineal ultrasound (transverse plane) was used to measure the pubic arch angle. Correlations with fetomaternal characteristics, mode of delivery and perinatal outcome were evaluated.

RESULTS

The mean PAA was 101.1° (± 13.1°; range, 80°-135°). We found a negative correlation with maternal age. Patients with an occipitotransverse fetal position had a significantly smaller angle compared with those with occipitoanterior positions (94.3° ± 5.5° vs. 103.2° ± 14.8°, P < 0.05), as did those with operative deliveries compared with those with spontaneous vaginal delivery (97.1° ± 11.5° vs. 110.1° ± 14.0°, P < 0.05). The prediction of operative delivery in prolonged second stage of labor by receiver-operating characteristics curve using PAA alone yielded an area under the curve of 0.75. The predicted probability for operative delivery increased as PAA decreased, with an odds ratio of 0.933 for each decrease in angle of 1°.

CONCLUSION

Our study suggests a correlation between the PAA and mode of delivery in prolonged second stage of labor. This may be used as an adjunctive parameter when considering delivery mode.

Can angle of progression in pregnant women before onset of labor predict mode of delivery?

OBJECTIVES

The angle of progression (AOP), measured by transperineal ultrasound, has been used to assess fetal head descent during labor. Our aim was to assess whether, before onset of labor, parous women have a narrower AOP than do nulliparous women and if a narrow AOP is associated with a higher rate of Cesarean delivery.

METHODS

In this prospective, observational study, we performed transperineal ultrasound in pregnant women not yet in labor at ≥ 39 weeks' gestation who delivered within 1 week of sonography. The AOP was compared as follows: in nulliparous women, between those who had a Cesarean section and those who delivered vaginally; and among women who delivered vaginally, between those who were nulliparous and those who were parous.

RESULTS

Included in the study were 100 nulliparous and 71 parous women. Among those who delivered vaginally (n = 161), the median AOP before onset of labor was narrower in parous than in nulliparous women (98° (interquartile range (IQR)), 90-107° vs 104° (IQR, 97-113°), P < 0.001). Among the 100 nulliparous women, (1) the median AOP before onset of labor was narrower in those who went on to deliver by Cesarean section (n = 9) than in those delivered vaginally (n = 91) (90° (IQR, 85.5-93.5°) vs 104° (IQR, 97-113°), P < 0.001); (2) an AOP ≥ 95° (derived from the receiver-operating characteristics curve) was associated with vaginal delivery in 99% of women; and (3) 89% (8/9) of women who delivered by Cesarean section had an AOP < 95°. Among the 71 parous women, only one delivered by Cesarean section and all of those with an AOP < 95° delivered vaginally.

CONCLUSION

A narrow AOP (< 95°) in non-laboring nulliparous women at term is associated with a high rate of Cesarean delivery. Parous women have a narrower AOP than do nulliparous women before the onset of labor; however, unlike in nulliparous women, a narrow AOP in parous women does not appear to be associated with Cesarean delivery and most parous women with such an angle go on to deliver vaginally.

Human birth observed in real-time open magnetic resonance imaging

OBJECTIVE

Knowledge about the mechanism of labor is based on assumptions and radiographic studies performed decades ago. The goal of this study was to describe the relationship between the fetus and the pelvis as the fetus travels through the birth canal, using an open magnetic resonance imaging (MRI) scanner.

STUDY DESIGN

The design of the study used a real-time MRI series during delivery of the fetal head.

RESULTS

Delivery occurred by progressive head extension. However, extension was a very late movement that was observed when the occiput was in close contact with the inferior margin of the symphysis pubis, occurring simultaneously with gliding downward of the fetal head.

CONCLUSION

This observational study shows, for the first time, that birth can be analyzed with real-time MRI. MRI technology allows assessment of maternal and fetal anatomy during labor and delivery.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Angle of progression measurements of fetal head at term: a systematic comparison between open magnetic resonance imaging and transperineal ultrasound

OBJECTIVE

During labor, transperineal sonography is increasingly used to evaluate fetal head descent. The aim of this study was to compare the angle of progression assessed by open magnetic resonance imaging (MRI) vs transperineal ultrasound.

STUDY DESIGN

A total of 31 pregnant women at term (>37 weeks), who were not in labor, underwent MRI in an open 1.0-T system. A midsagittal plane of the maternal pelvis was stored. Immediately after, without changing the supine position, a transperineal ultrasound was performed. The angle of progression was measured offline by transperineal ultrasound and MRI.

RESULTS

The angles of progression measured by transperineal ultrasound (mean, 79.05 degrees; SD 11.44) and MRI (mean, 80.48 degrees; SD 11.06) correlated significantly (P < .001). The intraclass correlation coefficient between the 2 methods was 0.89 (95% confidence interval, 0.78-0.94).

CONCLUSION

The angle of progression measurements obtained by transperineal ultrasound and open MRI showed very good agreement.

How the cervix shortens: an anatomic study using 3-dimensional transperineal sonography and image registration in singletons and twins

OBJECTIVES

The purpose of this study was to use a fixed reference to study movement (displacement) of the cervical internal os from the second to the third trimester in singletons and twins. The rationale was to gain insight into anatomic changes associated with cervical shortening.

METHODS

For each patient, 2 transperineal scans were performed 12 weeks apart (20 and 32 weeks). The internal os and symphysis pubis were visualized in the same field of view. Image registration techniques were used to align the 2 scans using the symphysis as a fixed reference. Total displacement, anterior displacement, and inferior displacement of the internal os were measured. Displacements were correlated with cervical shortening. Bland-Altman plots and interobserver intraclass correlation coefficients were calculated.

RESULTS

A total of 42 healthy participants were studied: 28 with singletons and 14 with twins. The mean ± SD values for total displacement were 2.1 ± 1.2 and 2.0 ± 1.2 cm for singletons and twins, respectively (P = .75). The direction of displacement was significantly different. The mean anterior displacement was 1.1 cm greater for singletons than for twins (95% confidence interval, 0.29-2.0 cm, P = .01). Mean inferior displacement was 1.3 cm greater for twins than for singletons (95% confidence interval, 2.2-0.1 cm; P = .03). Only inferior displacement correlated with cervical shortening (P < .001; R(2) = 0.74). For every 2.2 cm of inferior displacement, the cervix shortened 1.0 cm. Assessments of reliability showed good agreement between 2 observers.

CONCLUSIONS

The anatomic position of the internal cervical os depends on gestational age and fetal number. Cervical shortening correlated most strongly with inferior displacement.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

What is the most reliable ultrasound parameter for assessment of fetal head descent?

OBJECTIVES

The aims of this study were, first, to establish the agreement between digital and ultrasound assessment of occipital position and, second, to evaluate the repeatability of the measurements of head direction, angle of the middle line, progression distance and angle of progression in women in the second stage of labor.

METHODS

Digital examination and then transabdominal ultrasound examination was performed on 50 women in the second stage of labor to determine the fetal occipital position. We also obtained three-dimensional (3D) blocks of the fetal head by transperineal sonography, and two experts in 3D ultrasound measured head direction, angle of the middle line, progression distance and angle of progression. Intraclass correlation coefficients with 95% CIs, and Bland-Altman analysis, were used to evaluate intraobserver and interobserver repeatability of measurements.

RESULTS

The fetal head position, determined by ultrasound examination, was occiput anterior in 33 (66%) cases and occiput lateral in 17 (34%) cases. Vaginal digital examination failed to identify the correct fetal head position by more than 45° in 33 (66%) cases. All four 3D ultrasound measurements were reproducible but the progression angle had the highest intraclass correlation coefficient for the same observer (0.94; 95% CI, 0.90-0.97) and for two different operators (0.84; 95% CI, 0.73-0.91). The progression angle was also the measurement for which smaller limits of agreement (LOA) were found in the Bland-Altman test, performed to calculate the intraobserver (bias 0.9; LOA, - 9.2 to 11.1%) and interobserver (bias 1.5; LOA, - 15.4 to 18.3%) variability.

CONCLUSIONS

Digital pelvic examination for determining the fetal head position during labor is not accurate. The most reproducible of the 3D measurements for progression of the fetal head in labor is the progression angle.

Three-dimensional ultrasound in monitoring progression of labor: a reproducibility study

OBJECTIVE

The aim of this study was to evaluate the intraobserver and interobserver reproducibility of measurements, obtained from stored ultrasound volumes, related to fetal head progression in the birth canal.

METHODS

From January to September 2009, serial ultrasound volumes were obtained from women in labor, stored and separately evaluated by two different operators using the SonoVCAD™ labor software. Volumes were aligned using the pubic bone and the urethra as references. In the sagittal plane of the pelvis, the following data were calculated: head progression distance (the distance between the infrapubic line and the lowest part of the fetal skull), head direction (the angle between the infrapubic line and the major longitudinal axis of the fetal head) and head progression angle (the angle between the longitudinal axis of the pubic bone and a line joining the lowest edge of the pubis to the lowest convexity of the fetal skull). In the transverse plane, the angle formed by the midline with the anteroposterior axis of the maternal pelvis (midline angle) was also measured. For each measurement, intraobserver and interobserver reproducibility was determined.

RESULTS

We analyzed 30 ultrasound volumes. For all parameters, interobserver variation was significantly higher than intraobserver variation. Reproducibility was good for all parameters, except for the midline angle. Among the different ultrasound measurements, the progression angle presented the highest reproducibility.

CONCLUSIONS

Measurements obtained from stored ultrasound volumes to assess fetal head progression in the second stage of labor have good reproducibility, with progression distance and progression angle being the most reproducible parameters.

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.