Angle of Progression Measurements of Fetal Head at Term

8/2/2019 Angle of Progression Measurements of Fetal Head at Term

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OB STETRICS

Angle of progression measurements of fetal head at term: asystematic comparison between open magnetic resonance

imaging and transperineal ultrasoundChristian Bamberg, MD; Saskia Scheuermann, MD; Christina Fotopoulou, PhD; Torsten Slowinski, MD;Anna M. Dckelmann, MD; Ulf Teichgrber, PhD; Florian Streitparth, MD; Wolfgang Henrich, PhD;

Joachim W. Dudenhausen, PhD; Karim D. Kalache, PhD

OBJECTIVE: During labor, transperineal sonography is increasingly

used to evaluate fetal head descent. The aim of this study was to com-

pare 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 mid-

sagittal 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)andMRI (mean,80.48 degrees; SD 11.06)

correlated significantly (P .001). The intraclass correlation coefficient be-

tweenthe2 methods was0.89(95% confidenceinterval, 0.780.94).

CONCLUSION: The angle of progression measurements obtained by

transperineal ultrasound and open MRI showed very good agreement.Key words: angle of progression, labor, open magnetic resonance

imaging, translabial ultrasound, transperineal ultrasound,

ultrasonography

Cite this article as: Bamberg C, Scheuermann S, Fotopoulou C, et al. Angle of progression measurements of fetal head at term: a systematic comparison between

open magnetic resonance imaging and transperineal ultrasound. Am J Obstet Gynecol 2012;206:161.e1-5.

Various studies have shown that vag-inal palpation of fetal head stationis highly subjective, examiner depen-

dent, and thus not accurately reliable,

1,2

even though it is the standard practice

used to determine labor progress in all de-

livery units around the world.3 Neverthe-

less, during labor, transperineal sonogra-

phyis becoming an establishedmethod for

evaluating labor progress4-6 and the suc-

cess rate of vacuum extraction.

7

Barbera etal8 were the first to use transperineal ultra-

sound to measure the angle between the

maternal symphysis pubis and the leading

part of the fetal skull (angle of progres-

sion). There is growing evidence suggest-

ingtheangle ofprogressionmay constitute

a suitable, objective tool to evaluate labor

progress.

The goal of this study was to study theagreement in assessing angle of progres-

sion between open magnetic resonance

(MR) imaging (MRI) (the gold stan-dard) and transperineal ultrasound in

women at term, who were not in labor.

To our knowledge, this is the first study

describing MRI evaluation of the angle

of progression.

MATERIALS AND METHODS

From January 2009 through September

2009, we prospectively evaluated women

at term from our antenatal care unit. In-

clusion criteria were a live singleton

pregnancy of

37 completed weeks with afetus in an occiput anterior position. The

fetal headposition wasdiagnosed by trans-

abdominal ultrasound as previously de-

scribed by Akmal et al.9 Exclusion criteria

were known fetal abnormalities, pretermrupturedmembranes,activelabordemon-

strated by regular uterine contractions,

and contraindications to the use of MRI.

The study protocol was approved by the

local medical ethics committee. Informed

consent was obtained from all patients. All

31 healthy patients underwent MRI exam-

ination and, subsequently, a transperineal

ultrasound.

MRI was performed in a 1.0-T open

high-field MR scannerwitha verticalmag-

netic field orientation (Panorama; PhilipsHealthcare,Best, TheNetherlands)using a

body coil. Pregnant patients were exam-

ined with an empty bladder, in a supine

decubitus position, with appropriate pad-

ding. A T1-weighted fast spin-echo se-

quence was obtained using the following

settings: time of echo, 19 milliseconds;

time of repetition, 790 milliseconds; and

thickness, 3 mm. The total individual

study time was 30 minutes in all cases.

MRIs were analyzed offline (Figure 1, A);

on the basis of a midsagittal slice orienta-tion, the angle of progression was mea-

From the Departments of Obstetrics (Drs

Bamberg, Scheuermann, Dckelmann,

Henrich, Dudenhausen, and Kalache),

Gynecology (Dr Fotopoulou), Nephrology

(Dr Slowinski), and Radiology (Drs

Teichgrber and Streitparth), Charit

University Hospital, Berlin, Germany.

Received April 18, 2011; revised Aug. 18,2011; accepted Oct. 19, 2011.

This project was supported by a public grantfrom TSB (Technologiestiftung Berlin)Zufunftsfonds Berlin.

The authors report no conflict of interest.

Reprints: Christian Bamberg, MD, Departmentof Obstetrics, Charit University Hospital,Campus Virchow-Klinikum, AugustenburgerPlatz 1, 13353 Berlin, [email protected].

0002-9378/$36.00 2012 Mosby, Inc. All rights reserved.

doi: 10.1016/j.ajog.2011.10.867

Research www.AJOG.org

FEBRUARY 2012 American Journal of Obstetrics& Gynecology 161.e1
mailto:[email protected]:[email protected]:[email protected]


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sured by 1 radiologist, in the same way de-

scribed for the transperineal approach(see

below), who wasblinded to theultrasound

results.

Transperineal ultrasound studies were

performed immediately after the MRI

examinations without changing thewomens posture. We opted for this ap-proach to avoid any fetal head move-

ments between the MRI examination

and the transperineal ultrasound study.

A Voluson 730 Expert system equipped

with a 4- to 7-MHz transabdominal

3-dimensional transducer (GE Health-

care, Milwaukee, WI) was used. A single

experienced observer with10 years clin-

ical ultrasound practice quantified the an-

gle of progression using the method de-

scribed by our group.

6

Briefly, the probewas covered with a sterile glove and placed

on the midsagittal plane on the perineum.

First, small lateralmovements of the probe

were made until an image was obtained

that did notcontain shadows from thepu-

bic rami and showed a midsagittal view

with clear visualization of the pubic sym-

physis and fetal skull. The probe was then

displaced laterally until the pubic ramus

was clearly visualized within the symphy-

seal capsulartissue. Carewastaken toproj-

ect the acoustic shadow generated by thepubic ramus above the presenting part ofthefetalskullbytiltingthetransducer.Two

to 3 images were recorded for offline mea-

surement of the angle of progression (the

angle between a line placed through the

midline of the pubic symphysis along

the pubic ramus and a line running from

the inferior apex of the symphysis tangen-

tially to the most anterior part of the fetal

skull) (Figure 1, B). The sonographer was

blinded to the MRI data.

Allresultsarepresentedinrawnumbers,rates, medians and ranges, or means SD

according to the underlying distribution.

Data were first tested for normality and

equal variance (Kolmogorov-Smirnov

test). We used paired t test to compare

the relationship of the angles of progres-

sion measured by transperineal ultra-

sound and open MRI. The intraclass cor-

relation coefficient (ICC); 95% confidence

interval (CI) for the ICC and the Bland-

Altman method for assessing agreement,

including calculation of the average dis-crepancy between measurements (bias);

FIGURE 1

Images in same woman

A

BB

Angles of progression measured by A, open magnetic resonance imaging, and B, transperineal

ultrasound.

Bamberg. Angles of progression measured by transperineal ultrasound and openMRI. Am J Obstet Gynecol 2012.

Research Obstetrics www.AJOG.org

161.e2 American Journal of Obstetrics & Gynecology FEBRUARY 2012


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the 95% limits of agreement; and the SD

of bias were generated to illustrate the

differences between angles of progres-

sion measured by open MRI and trans-

perineal ultrasound. Statistical analysis

was performed using software (SPSS

16.0; SPSS Inc, Chicago, IL). Software(GraphPad Prism, version 4.0 for Mac

OSX; GraphPad Software, San Diego,

CA) was also used for graphing. For all

tests, P .005 was considered statisti-

cally significant.

RESULTS

During the study period, 31 patients

were enrolled and included in this anal-

ysis. The mean age was 29 years (range,

18 38), whereas the median gravidity

was 2 (range, 15) andmedian paritywas1 (range, 02). Detailed maternal and

pregnancy-related characteristics are

summarized in the Table. The majority

of the evaluated patients (58%) had a

spontaneous vaginal delivery, whereas 9

patients (29%) underwent a cesarean sec-

tion. The mean birthweight was 3284

513 g for full-term newborns.

All attempts to measure angles of pro-

gression with transperineal ultrasound

and open MRI were successful. The val-

ues of the angles of progression mea-sured by both methods showed a normal

distribution. 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) (Fig-

ures 2 and 3). The intraclass correlation

was 0.89 (95% CI, 0.780.94). Figure 4shows a Bland-Altman graph, compar-

ing the angle of progression differences

between transperineal ultrasound and

open MRI. The mean difference was 1.4

degrees 6.75 SD with 95% limits ofagreement from 14.9 to 12 degrees.

COMMENT

In this study, we showed there was very

good agreement between measurements

of the angle of progression obtained by

transperineal ultrasound and open MRI.Transperineal ultrasoundis a novel tech-

nique, which is increasingly being used

to evaluate fetal head descent during la-

bor.4-6,10 This method was established

because digital vaginal examination of

head station during labor is operator de-

pendent and poorly reproducible.11-13

Barbera et al4 measured the angle of

progression in 88 laboring patients in the

second stage of labor and found an angle

120 degrees was always associated with

a subsequent spontaneous delivery. Wepreviously reported that measuring the

angle of progression could assist in the

obstetricians decision to attempt a vag-

inal delivery or cesarean section. An an-

gle of progression of120 degrees in an

occiput anterior fetal position was asso-

ciated with a 90% probability of success-ful vaginal delivery.6

Very recently, our group showed a sig-

nificant correlation between the angle of

progression observed by transperineal

ultrasound and the distance between the

leading bone edge of the fetal cranium

and the maternal ischial spines depicted

by open MRI.14 Based on statistical as-

sumption,station 0 would correspond to

a 120-degree angle of progression.

In this evaluation, we showed angle of

progression measurements at term can beaccurately assessed by transperineal ultra-

sound as it presents a highly statistically

significant correlation with equivalent

MRI measurements, which are reproduc-

ible and not examiner dependent. How-

ever, several limitations of our study must

be addressed. Results are based on a rela-

tively small number of enrolled patients.

None of the women in this investigation

were in labor, and none of the fetal heads

were engaged. The average angle of pro-

gression was about 80 degrees, which cor-relatesfromourpreviouspublisheddatato

FIGURE 2

Box and whiskers plot showsdistribution of angle ofprogression measured bytransperineal ultrasoundand MRI

MRI, magnetic resonance imaging.

Bamberg. Angles of progression measuredby transperinealultrasound andopenMRI.Am J ObstetGynecol2012.

TABLE

Maternal and pregnancy characteristics of study population

Characteristic Value [range]

Maternal age, y 29.5 5.3 [1838]..............................................................................................................................................................................................................................................

Gestational age at enrollment, wk 38.3 1.6 [3741]..............................................................................................................................................................................................................................................

Parity.....................................................................................................................................................................................................................................

Nulliparous 18 (58).....................................................................................................................................................................................................................................

Multiparous 13 (42)..............................................................................................................................................................................................................................................

Maternal height, cm 163.9 7.7 [143186]..............................................................................................................................................................................................................................................

Maternal weight at enrollment, kg 74.9 10.9 [5691]..............................................................................................................................................................................................................................................

Gestational age at delivery, wk 39.2 1.0 [3741]..............................................................................................................................................................................................................................................

Mode of delivery.....................................................................................................................................................................................................................................

Spontaneous 18 (58).....................................................................................................................................................................................................................................

Instrumental 4 (13).....................................................................................................................................................................................................................................

Cesarean 9 (29)..............................................................................................................................................................................................................................................Birthweight, g 3284 513 [22404180]..............................................................................................................................................................................................................................................

Data are presented as mean SD or as total number (%).

Bamberg. Angles of progression measuredby transperineal ultrasound and openMRI. Am J Obstet Gynecol 2012.

www.AJOG.org Obstetrics Research



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a fetal head station 3-4 cm above the level

of the ischial spines.14 The fundamental

premise that has been used to label station

is that the first part of the birth canal is

straight and the second part below the in-

terspinous level has a curvilinear trajec-

tory.

15

In this model, an increased angle ofprogression up to 120 degrees would cor-respond to a proportional descent in fetal

head station until head engagement. We

are aware that most published angles of

progression wereacquired during labor.4-6

Itisyettobeshownifthesefindingscanbe

correlated to patients in labor. Further in-

vestigation into this aspect would help to

resolve this issue. Although, Dietz and

Lanzarone16 established the pubic sym-

physis as a landmark for transperineal ul-

trasound before labor and examined itsreproducibility.

Even if it would haveadded strengthto

the study having 2 observers, the re-

producibility of transperineal ultra-

sound has been reported and found to be

good. Molina et al17 showed the angle of

progression is the most reliable ultra-

sound parameter to assess fetal head de-

scent. In 50 women in the second stage of

labor, 2 experts performed 3-dimen-

sional volume acquisition of the fetal

head by transperineal sonography andcompared the results of head direction,angle of midline, progression distance,

and angle of progression. The angle of

progression had the highest ICC for the

same observer (0.94) and 2 different

(0.84) observers. Furthermore, these

measurements had the smallest limits of

agreement in the Bland-Altman test for

the intraobserver and interobserver vari-

ability, respectively.17 These findings are

very similar to those of Dckelmann et

al18

who used a 2-dimensional ultra-sound system to examine the angle of

progression in 24 women in prolonged

second stage of labor and reported that

the ICC of separate images acquired by 2

experienced sonographers was 0.82 (95

CI, 0.70 0.89). The mean differences in

the angle of progression measurements

between an observer with 10 years ul-

trasound experience vs an observer with

5 years experience were similar and

small.

In clinical settings, measurement com-parisons of 2 different methods are often

FIGURE 3

Scatterplot of angles of progression measured by 2 differentmethods, linear regression model fits curve best


FIGURE 4

Bland-Altman diagram shows good agreement for offline analysisof angle of progression between open MRI and transperineal US

Solid linerepresents mean and dotted line1.96 SD.

MRI, magnetic resonance imaging; US, ultrasound.


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161.e4 American Journal of Obstetrics & Gynecology FEBRUARY 2012


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needed to determine whether they agree

sufficiently. The use of correlation is mis-

leading. Data that are in poor agreement

can produce quite high correlations, and

the testof significanceis inappropriatelyto

the question of agreement. Bland and Alt-

man

19,20

deviseda simple,but informative,way of graphing the comparison of 2 assay

methods. Therefore, we used the limits of

agreement approach and Bland-Altman

graphing of the difference between the

methods against their mean.19,20 The 2

methods had very similar results on aver-

age, and the difference between the means

was only 1.4 degrees. In 95% of subjects,

the angles lie between 14.9 and 12 de-

grees. The differences between measure-

ments remainedstable as theaverage angle

of progression increased.Open MRI systems were designed to

allow better patient access and to in-

crease patient comfort.21 The higher

field strength (1.0 T) in combination

with an open configuration of the mag-

net is therefore desirable to obtain high

MRI quality.22 We used a T1-weighted

fast spin-echo sequence with a midsagit-

tal view for assessment of the fetal head

stationand for measurement of the angle

of progression. As mentioned by Paltieli

and Nizard,23

ultrasound measurementsof angle of progression use the non-bony

pubic symphysis landmark, whereas

computed tomography derived data are

obtained by considering bony land-

marks. A strict midsagittal section has

the advantage of obtaining an image

without an acoustic shadowfrom thepu-

bic ramus. This view allows clear visual-

ization of the presenting part but might

present a challenge when defining the

long axis of the symphysis. We suggest

slightly displacing theprobeuntil the pu-bic ramus is clearly visualized within the

symphyseal capsular tissue.24

In conclusion, to confirm the validity of

the angle of progression measurement by

transperineal ultrasound, we have now

testedthis method by comparingit to MRI

(the gold standard). From practical and

clinical points of view, the discrepancy be-

tween the 2 methods is very small. Further

confirmationstudies areneeded to validate

transperineal ultrasound imaging measure-

ments of theangle of progression in the as-

sessment of labor. Clinical trials demon-

stratingbenefitsoftheuseofthistechnique

in practical obstetrics are warranted. We

propose that transperineal ultrasound

measurement of the angle of progressioncan be clinically beneficial in laboring

patients. f

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Angle of Progression Measurements of Fetal Head at Term