Fetal Head Station Research Articles

Determination of Fetal Head Station and Position During Labor: A New Technique That Combines Ultrasound and a Position-tracking System

Determination of Fetal Head Station and Position During Labor: A New Technique That Combines Ultrasound and a Position-tracking System

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

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. 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. 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). 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.

The role of instrumental vaginal delivery in low resource settings

This commentary discusses instrumental vaginal delivery (IVD) and the issues experienced with that practice in low resource settings. It states that IVD is a key element of essential obstetric care and the improvement of maternal and neonatal outcomes will require the scaling up of IVD use with the provision of equipment and trained operators to areas where they are currently unavailable.

OP01.05: Relationship between cervical dilatation and fetal head station using an ultrasound and position tracking system. Do we need cervical examination?

OP01.05: Relationship between cervical dilatation and fetal head station using an ultrasound and position tracking system. Do we need cervical examination?

OP01.09: Correlation between two different non invasive approaches to measure fetal head station: angle of progression and LaborPro system

OP01.09: Correlation between two different non invasive approaches to measure fetal head station: angle of progression and LaborPro system

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Relations between fetal head descent and cervical dilatation during individual uterine contractions in the active stage of labor

The relationship between instantaneous changes in fetal head station and cervical dilatation within the individual contraction during the active stage of labor were studied and an index of labor progress was suggested. Cervix dilatation and fetal head station were measured continuously in 30 nullipara women (mean age 27.5, standard deviation 4.8). The continuous measurements enabled the analysis of each variable and the analysis of the relations between these two variables. The relationship between the head station and the cervical dilatation were demonstrated by plotting one against the other during a contraction. This led to the definition of a contraction vector that integrates the interaction between the two variables. The angle of this vector, that indicates this relation, was plotted against mean head station to demonstrate change along the delivery process regardless of time to normalize the progress and allow comparison between different women with different labor durations. This plot showed a sharp change from almost zero into a steep curve at about zero head station. A zero angle indicates that the cervix dilates during a contraction with little effect on head station while a steep angle indicates a significant effect of cervical dilatation on head station during the contraction. The contraction-vector angle reflects the changing intra-contraction relationship between head station and cervical dilatation. The angle of this vector may serve as an indicator of labor progress.

Diagnostic échographique d’engagement de la présentation fœtale. À propos d’une série prospective préliminaire française

The subjectivity and inter- and intra-observer variability of transvaginal (TV) digital examination in the diagnosis of fetal head engagement set a real problem in the strategic choice of the mode of delivery. We conducted a preliminary study on the feasibility of using ultrasound in the diagnosis of fetal head engagement during labour. From 3rd January to 20th February 2007, a prospective monocentered study was set up by comparing the fetal head position in the pelvic cavity obtained by TV digital examination with the ultrasound measurement of the perineum-fetal head distance. Sixty-five measurements were obtained from 45 patients (single pregnancies, cephalic presentations), during labour and/or at complete cervical dilatation, by a single operator. Whenever the perineum-fetal head distance was greater than 60 mm, the fetal head was not engaged in the pelvic cavity, with a specificity of 89% and a negative predictive value of 94.1%. However, if the distance is less or equal to 60 mm, the fetal head was engaged with a sensitivity of 97.8% and a positive predictive value of 95.6%. It was even possible to define the fetal head station in the cavity as the distances are now known: high cavity : 50 mm, mid cavity : 38 mm, low cavity : 20 mm. This technique based on a single distance measurement is not difficult and the reference point is easily localized. An abdominal probe is sufficient, making the diffusion of this method quite easy. With its excellent negative predictive value, transperineal ultrasound would allow obstetricians avoid difficult vaginal extractions, localize correctly the fetal position in the cavity and obtain the exact fetal head orientation, even in case of scalp blood humps. The feasibility and relevance of this technique must be confirmed by larger studies.

The validity and reliability of the StationMaster: A device to improve the accuracy of station assessment in labour

Objective To compare the accuracy of digital assessment and the StationMaster (SM) in the assessment of fetal head station. The SM is a simple modification of the amniotomy hook which works by relocating the point of reference for station assessment from the ischial spines to the posterior fourchette. It is first adjusted to the woman's pelvic size, and then inserted into the vagina until it touches the fetal head. The station is then read off at the posterior fourchette in cm. Study design An in vitro study of test validity and reliability was conducted at Liverpool Women's Hospital, Liverpool, UK. An apparatus was constructed in which a model fetal head could be accurately positioned within a mannequin's pelvis. Twenty midwives and 20 doctors (in current labour ward practice) gave their consent to take part. First, the head was placed in 5 random stations (−2 to +7 cm) and the participant asked to record their digital assessment for each. The participant was then taught to use the SM and the experiment repeated with 5 new stations. The complete experiment was repeated at least 2 weeks later using the same stations but in reverse order. The true values were compared with both the digital and SM assessments using mean differences with 95% limits of agreement. The repeatability of the two methods was assessed in the same way. Results Overall, the SM was more accurate than digital examination. The mean error (S.D.) ranged from 0.1 (1.2) to 2.6 (1.6) for the StationMaster and 0.3 (1.3) to 4.3 (1.1) for digital examination. Inaccuracies increased as the head descended through the pelvis. When assessed digitally, the true value fell outside one standard deviation for stations of more than +1 cm. In contrast, with the SM the true value remained inside one standard deviation for all stations up to +5. Conclusions In vitro the SM improves the accuracy of intrapartum station assessment.

Role of a second stage partogram in predicting the outcome of normal labour

Management of the second stage of labour is dictated by arbitrary time limits rather than true measures of progress. No partogram is available for second stage of labour. To evaluate a partogram designed for use for the second stage of labour. This prospective cross-sectional analytical study included low-risk pregnant women with singleton fetuses with vertex presentations at term. From onset of the second stage, vaginal examinations were performed every 30 min until delivery. A scoring system developed by Sizer et al. was used based on station and position of fetal head. Scores were plotted on a second stage partogram and used to predict labour outcomes, such as duration of second stage and mode of delivery. Of 79 women examined, 73 had spontaneous vaginal delivery. Of the remaining six, four required oxytocin infusion and other two required vacuum extraction. The median durations of the second stage of labour for primigravidas (n = 34) and multigravidas (n = 45) were 35 and 25 min, respectively. The median Sizer's partogram score at the onset of second stage was 4. Multiple regression analysis showed that the partogram score (r2 = 0.27) and gravidity (r2 = 0.10) were independent predictors of duration of the second stage. There was a significant association between second stage progress plotted to the right of the partogram line and non-spontaneous delivery (P = 0.01). The second stage partogram score at onset can predict the duration of second stage. Poor progress plotted on the partogram is associated with non-spontaneous delivery.

Effects of the individual uterine contraction on fetal head descent and cervical dilatation during the active stage of labor

Objective To evaluate the effects of individual uterine contractions on instantaneous values of cervical dilatation and head station along the active stage of labor. Study design Cervix dilatation and fetal head station were measured continuously using a labor monitor that is based on ultrasonic triangulation. The relations between the two variables in response to each contraction were analyzed. The relative effect of the contraction on head station and on cervical dilatation was demonstrated by plotting one against the other during the contraction and quantified by two indices: (a) the contraction vector that integrates the maximum effect of uterine contraction on both variables and (b) the efficiency vector that indicates the contribution of each contraction to labor progression. The amplitude and angle of each vector were calculated. Correlation between the waveforms of head station and cervix dilatation during contractions was also calculated. These indices were plotted against cervix dilatation and head station at different stages in labor progress. Results Effects of uterine contractions on cervix dilatation and head station varied during labor. The amplitude of the contraction vector and efficiency vector increased to a maximal value at cervical dilatation of 6 cm. The angle of the contraction vector increased with the progress of labor. Correlation between cervical dilatation and head station was maximal at the engagement zone of the birth canal. High variability was observed between subjects for all indices measured. Conclusion The contraction vector and the efficiency vector exhibited distinct behavior during labor. These vectors may serve as indicators for normal and abnormal progress of labor. More data are required to obtain statistical significance.

A new method to assess fetal head descent in labor with transperineal ultrasound

To assess the feasibility and reproducibility of measuring fetal head station and descent during labor using transperineal ultrasound (TPU) imaging, to compare the evaluation of fetal station through digital examinations with concurrent TPU assessments, and to assess its utility in distinguishing patients whose pregnancy will result in spontaneous vaginal delivery from those who will require operative vaginal delivery or Cesarean section for failure to progress. TPU and digital examinations were performed in 88 term laboring patients with a singleton fetus in cephalic presentation. Using TPU imaging, head descent was quantified by measuring the angle between the long axis of the pubic symphysis and a line extending from its most inferior portion tangentially to the fetal skull. Intraobserver and interobserver variability were calculated using variance component analysis. TPU imaging was used to measure the angle of head descent during the second stage of labor in 23 of the women. Analysis of replicated measurements on 75 subjects, by the same observer at approximately the same time, yielded an average SD (intraobserver variability) of approximately 2.9 degrees for the measurement of angle of head descent on TPU examination. A separate variance component analysis on a subset of 15 assessments for which measurements were repeated by a second observer, with two to four replicate measurements obtained by each, yielded an interobserver error estimate of 1.24 degrees. A significant linear association was found between clinical digital assessments and measurement of angle of head descent by TPU examination (P < 0.001). An angle of at least 120 degrees measured during the second stage of labor was always associated with subsequent spontaneous vaginal delivery. In six pregnancies ending in Cesarean section the mean angle of descent measured at last TPU examination was only 108 degrees. The angle of head descent measured by TPU imaging provides an objective, accurate and reproducible means for assessing descent of the fetal head during labor.

Anatomic relationship between the pubic symphysis and ischial spines and its clinical significance in the assessment of fetal head engagement and station during labor

To develop a geometric model from computed tomographic (CT) images in non-pregnant women that would objectively reflect clinical head station in laboring patients, against which to test the accuracy of digital examinations. CT scans were performed in 70 non-pregnant women to determine, using a geometric model, which angle in a mid-sagittal transperineal ultrasound (TPU) image best coincided with the mid-point of a line drawn between the ischial spines (zero station). Using a geometric algorithm, TPU angles were then assigned for other clinical stations (-5 to + 5). Finally, clinical station was assessed by digital examination and simultaneous TPU assessments in 88 laboring patients to see how closely the clinical examination correlated with the station calculated from the above geometric model. The mean angle between the long axis of the symphysis pubis and the mid-point of the line connecting the two ischial spines for the 70 non-pregnant subjects was 99 degrees . The geometric model developed allowed us to build an algorithm to assign a specific set of theoretical angles to each computed station. Relationships between digitally assessed fetal head station, TPU angle for each station, and the geometrical model created with CT data, are reported. Clinical digital assessment of station correlated poorly with computed station, especially at stations below zero, where it could have greater clinical impact. The TPU angle of 99 degrees correlated with zero station, and each station above or below this station could be assigned a specific corresponding angle for reference.

Determination of fetal head station and position during labor: a new technique that combines ultrasound and a position-tracking system

The purpose of this study was to compare the ultrasound-based LaborPro (Trig Medical Ltd, Yokneam, Israel) system determination of fetal head station and position with routine vaginal examination. This prospective study, which was conducted in 3 centers included 311 measurements that were performed in 166 singleton term pregnancies during the active phase of vertex, uncomplicated labor. Ultrasound-based position-tracking system calculations of fetal head station and position were compared with routine vaginal examination measurements. Comparison of vaginal examination with the system head station results revealed a mean absolute difference of 5.5 +/- 6.1 mm (n = 311). Vaginal examination head-position evaluation, within a 45 degrees interval, complied with the system in 35 of 87 cases (40.2%). Our data show that an ultrasound-based system can determine fetal head station and position during labor, when compared with vaginal examination, and requires minimal ultrasound skills. The limits of vaginal examination assessment of the head position are in agreement with published data.

209: Relation between fetal head station using the laborpro system and cervical dilatation determined by vaginal examination

209: Relation between fetal head station using the laborpro system and cervical dilatation determined by vaginal examination

226: Automated determination of fetal head station and position during labor: A new technique combining ultrasound and a position tracking system

226: Automated determination of fetal head station and position during labor: A new technique combining ultrasound and a position tracking system

Interobserver agreement in intrapartum estimation of fetal head station

Objective To determine interobserver agreement in estimation of fetal head station during labor, and the determinants of agreement. Methods A prospective study of fetal head station in 508 women in term labor. Vaginal examination of station was performed by a researcher at the same time as clinicians performed routine intrapartum assessments of the participants. Station 0 was considered to represent engagement. Results Station could be estimated by both the researcher and clinicians in 446 women (88%). The kappa statistic for agreement was 0.23 (95% confidence interval, 0.17–0.29). There was agreement in 166 cases (37%) and disagreement by 1 cm in 208 (47%) cases. Agreement was best (50%) when the researcher assessed the head at station minus 1. Multiple regression analysis showed that agreement was not influenced by level of experience of the attending clinicians, nor by obstetric factors. Conclusion Estimation of station as a method of determining the level of the fetal head in labor appears imprecise and poorly reproducible.

OC190: Comparison of three ultrasound‐based methods of determining the fetal head station with transvaginal digital examination

OC190: Comparison of three ultrasound‐based methods of determining the fetal head station with transvaginal digital examination

OP11.04: Infrapubic intrapartum ultrasound (iiUS): sonographic landmarks and correlation with successful vacuum extraction

Objective: Assessment of fetal head station is of importance before instrumental vaginal delivery. We have established a simple method of performing intrapartum infrapubic ultrasound (iiUS). Relating the fetal skull to the symphysis in laboring women during pushing and prior to vacuum extraction, we defined sonographic criteria for successful instrumental vaginal delivery. Methods: Sonographic assessment of the female pelvis in term pregnancies was performed in women with singleton pregnancies in the second stage of labor and after rupture of membranes. Anatomic landmarks were determined sonographically from sagittal infrapubic insonation with a curved array transducer. A 3D CT volume was used to correlate the normal anatomy of the female pelvis with these iiUS-derived landmarks. 20 women with singleton fetuses were studied immediately before vacuum extraction. Results: With a transducer placed infrapubically in a median sagittal orientation (‘infrapubic plane’), landmarks are: (1) the infrapubic line, placed perpendicular to the long axis of the pubic symphysis; (2) the widest fetal head diameter and its movement with regard to the infrapubic line during pushing; and (3) the ‘head direction’ as the angle between the long axis of the symphysis and a line perpendicular to the widest head diameter. CT reconstruction demonstrated the infrapubic line to be 3 cm cranial to the parallel interspinous plane. In 20 vacuum deliveries, the ‘head up’ sign (head pointing ventrally) and objective descent of the fetal head below the infrapubic line, both noted at the height of pushing, were associated with successful delivery. Lack of decent/lack of passage below the infrapubic line and horizontal or even downward head direction were poor prognostic signs. Conclusions: Intrapartum infrapubic ultrasound (iiUS) can provide information about the dynamics of the second stage of labor, head station and head direction. It may be used to assess prognosis for instrumental vaginal delivery.

P11.12: Determination of fetal head station during labor—an innovative method combining ultrasound and spatial positioning

P11.12: Determination of fetal head station during labor—an innovative method combining ultrasound and spatial positioning