Akmal S. Intrapartum sonography. Ultrasound Obstet Gynecol 2004.PDF

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Ultrasound Obstet Gynecol2004;24: 421424Published online 21 June 2004 in Wiley InterScience (www.interscience.wiley.com).DOI:10.1002/uog.1065

Intrapartum sonography to determine fetal occipitalposition: interobserver agreement

S. AKMAL, E. TSOI and K. H. NICOLAIDES

Harris Birthright Research Centre for Fetal Medicine, Kings College Hospital, London, UK

K E Y W O R D S: fetal occipital position; labor; sonography

ABSTRACT

Objective To investigate the interobserver agreement on

the intrapartum ultrasonographic definition of the fetaloccipital position.

Methods In 60 singleton pregnancies in labor at term thefetal occipital position was determined by transabdominalultrasound by two appropriately trained sonographerswho were not aware of each others findings. TheBlandAltman plot was performed and the 95% limitsof agreement were calculated. Logistic regression analysiswas used to investigate the association between completeagreement in the fetal occipital position between the twoobservers and maternal and labor characteristics.

Results The two observers had complete agreement on

the fetal occipital position in 22/60 (36.7%) cases anddisagreement by 15 and 30 in 31 (51.7%) and seven(11.6%) cases, respectively. The mean of the differencesbetween the two observers was 0.25 and the 95% limitsof agreement were 28.9 (32.2 to 25.6) to 29.4

(26.1 to 32.7). There were no significant associationsbetween complete agreement and maternal and laborcharacteristics.

Conclusion The interobserver agreement on sonograph-ically determined fetal occipital position during labor iswithin 15 in nearly 90% of cases and within 30 inall cases. Copyright 2004 ISUOG. Published by John

Wiley & Sons, Ltd.

INTRODUCTION

Intrapartum clinical assessment of the fetal occipitalposition is an integral part of routine monitoring inlabor, but recent studies on intrapartum sonographyreported that such clinical assessment is often inaccurate

(Table 1)16. Nevertheless, accurate determination ofthe fetal occipital position is important. First, thereis evidence that in women undergoing induction of

labor, preinduction sonographically determined occipitalposition, in addition to cervical length and traditionalmaternal characteristics, is superior to the Bishop scorein the prediction of the outcome of induction7. Second,malposition in labor is associated with higher rates ofCesarean section and maternal and neonatal morbidity8,9.The risk of Cesarean section can be estimated duringthe early stage of active labor by the sonographicallydetermined occipital position, in addition to traditionalmaternal, fetal and labor-related characteristics10. Third,an important determinant of successful and safe use ofthe vacuum and forceps is correct determination of thefetal occipital position. However, a sonographic study hasdemonstrated that clinical assessment during instrumentaldelivery fails to identify the correct occipital position inabout 25% of cases, suggesting that ultrasonographyshould be performed routinely before instrumentaldelivery6.

The aim of this study was to examine the degree ofagreement between two operators in determining fetaloccipital position by intrapartum sonography.

METHODS

In 60 singleton pregnancies in labor at term, with cervical

dilatation of 310 cm, the fetal occiput position wasdetermined sonographically by two appropriately trainedsonographers (Certificate of Competence; The FetalMedicine Foundation (http://www.fetalmedicine.com))who were not aware of each others findings. The twoexaminations were carried out within 3 min of each other.Thepatients provided written consent to participate in thestudy.

Ultrasonographic examination was performed transab-dominally with the patient in a supine position2. The

Correspondence to:Professor K. H. Nicolaides, Harris Birthright Research Centre for Fetal Medicine, Kings College Hospital MedicalSchool, Denmark Hill, London SE5 8RX, UK (e-mail: [email protected])

Accepted: 14 November 2003

Copyright 2004 ISUOG. Published by John Wiley & Sons, Ltd. ORIGINAL PAPER


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422 Akmal et al.

Table 1Studies examining the agreement between clinically andsonographically determined fetal occiput position during labor

Study n Study populationAgreement

(n(%))

Shereret al. (2002)1 102 First stage of labor 48 (47)

Akmalet al. (2002)2

496 First and secondstages of labor

163 (33)

Soukaet al. (2003)3 334 First and secondstages of labor

152 (46)

Kreiseret al. (2001)4 44 Second stage oflabor

31 (70)

Shereret al. (2002)5 112 Second stage oflabor

68 (61)

Akmalet al. (2003)6 64 Preinstrumentaldelivery

47 (73)

Agreement was considered to be present if the occiput positiondefined by the two methods was within 45 of each other, exceptin the study of Keiser et al.4 in which there was agreement on thedefinition of the occiput as anterior, posterior, left transverse or

right transverse.

ultrasound transducer was first placed transversely in thesuprapubic region of the maternal abdomen. The land-marks depicting fetal position were the fetal orbits foroccipito-posterior position, the midline cerebral echo foroccipito-transverse positions and cerebellum or occiputfor occipito-anterior position. For the latter the fetal spinewas demonstrated in its sagittal plane and traced from thefetal thoraxto theocciput. Theultrasound findings of fetaloccipital position were recorded on a datasheet depictinga circle, like a clock, with 24 divisions; for example, directocciput anterior, posterior and right transverse positionswere recorded as 0, 180 and 270, respectively. Thefindings of Observer A were expressed as an angle ofdeviation from those of Observer B.

Statistical analysis

The BlandAltman plot (difference between the twoobservers in occipital position in degrees against theaverage between the two) was performed and the 95%limitsof agreement (with their 95% CIs) wascalculated11.Logistic regression analysis was used to investigate theassociation between complete agreement in the fetaloccipital position between the twoobserversandmaternaland labor characteristics. Maternal age, body mass index,birth weight, gestational age, cervical dilatation anddescent of the presenting part were used as continuousnumerical variables. A score was given for ethnicity (1 forCaucasian, 2 for Afro-Caribbean and 3 for Asian), parity(0 fornulliparous,1 forparous), useof epidural anesthesiaor oxytocin (0 for No, 1 for Yes), sonographicallydetermined placental position (1 for anterior, 2 forposterior), occipital position defined by Observer A (1

for anterior, 2 for transverse, 3 for posterior) and modeof delivery (1 for spontaneous delivery, 2 for instrumentaldelivery, 3 for Cesarean section).

Measurements of Observer A

4003002001000

MeasurementsofObserverB

400

300

200

100

0

Figure 1BlandAltman scatter plot of occipital position (indegrees) by Observer A vs. Observer B.

Mean between paired measurements (degrees)

Differencebetweenmeasurements(degrees)

60

45

30

15

0

15

30

45

60

36031527022518013590450

Figure 2BlandAltman plot of the difference against the averageof the occipital position (in degrees) between Observer A andObserver B.

0

5

10

15

20

25

30

35

40

30 15 0 15 30

Difference between observers (degrees)

Observa

tions(%)

45

Figure 3BlandAltman histogram of the differences in occipitalposition (in degrees) between Observer A and Observer B.

RESULTS

The two operators had complete agreement on thefetal occipital position in 22/60 (36.7%) cases and

Copyright 2004 ISUOG. Published by John Wiley & Sons, Ltd. Ultrasound Obstet Gynecol2004;24: 421424.


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Intrapartum sonography 423

Table 2Characteristics of the population and results of the univariate analysis on the associations with the incidence of complete agreementbetween the two observers on the fetal occipital position

Characteristic n(%) or median (range) Odds ratio (95% CI) P

Age (years) 28 (1840) 1.04 (0.941.16) 0.432Ethnicity 0.180

Caucasian 26 (43.3%) 1Afro-Caribbean 8 (13.4%) 0.33 (0.061.97)Asian 26 (43.3) 0.37 (0.121.17)

Body mass index 24 (1840) 1.10 (0.981.24) 0.122Parity

Nulliparous 38 (63.3%) 1Parous 22 (36.7%) 0.72 (0.242.127) 0.554

Gestational age (weeks) 40 (3741) 1.33 (0.822.14) 0.244Use of oxytocin

No 31 (51.7%) 1Yes 29 (48.3%) 0.833 (0.292.39) 0.734

Epidural anesthesiaNo 31 (51.7%) 1Yes 29 (48.3%) 0.83 (0.292.39) 0.734

Cervical dilatation (cm) 7 (310) 1.01 (0.811.27) 0.880

Station (cm)* 0.90 (0.561.47) 0.6922 22 (36.7%)1 15 (25.0%)0 14 (23.3%)+1 9 (15.0%)

Occipital position 0.204Anterior 27 (45.0%) 1Transverse 17 (28.3%) 3.21 (0.8911.60)Posterior 16 (26.7%) 1.71 (0.456.47)

Placental position 0.913Anterior 24 (40.0%) 1Posterior 36 (60.0%) 0.94 (0.322.74) 0.864

Mode of deliveryVaginal 42 (70%) 1Instrumental 9 (15%) 0.90 (0.204.13)

Cesarean 9 (15%) 1.44 (0.346.20)Birth weight (kg) 3.49 (2.474.51) 1.00 (0.99 to 1.00) 0.400

*Distance of the presenting part from the ischial spines (, above; +, below).

disagreement by 15 and 30 in 31 (51.7%) and seven(11.6%) cases, respectively. The mean of the differencesbetween the two observers was 0.25 and the 95%limits of agreement were 28.9 (32.2 to 25.6) to29.4 (26.1 to 32.7) (Figures 13). The characteristicsof the population examined and the results of theunivariate analysis on the associations with the incidenceof complete agreement on occipital position between thetwo observers are shown in Table 2. There were nosignificant associations.

D I S C U S S I O N

The results of the present study demonstrate that theinterobserver agreement on sonographically determinedfetal occipital position during labor is within 15 in nearly90% of cases and within 30 in all cases. Furthermore,reproducible results were obtained irrespective of thematernal and labor characteristics examined (Table 2).

For sonographers with experience in obstetric scanning,determination of the fetal position, based on suchlandmarks as the fetal orbits, cerebellum, midline

echo of the brain and occiput, is easy and highlyreproducible.

ACKNOWLEDGMENT

The study was funded by The Fetal Medicine Foundation(Registered Charity No. 1037116).

REFERENCES

1. Sherer DM, Miodovnik M, Bradley KS, Langer O. Intrapartumfetal head position I: comparison between transvaginal digitalexamination and transabdominal ultrasound assessment duringthe active stage of labor. Ultrasound Obstet Gynecol2002;19:258263.

2. Akmal S, Tsoi E, Kametas N, Howard R, Nicolaides KH.Intrapartum sonography to determine fetal head position.

J Matern Fetal Neonatal Med2002;12: 172177.3. Souka AP, Haritos T, Basayiannis K,Noikokyri N,Antsaklis A.

Intrapartum ultrasound for the examination of the fetal headposition in normal and obstructed labor. J Matern FetalNeonatal Med2003;13: 5963.

4. Kreiser D, Schiff E, Lipitz S, Kayam Z, Avraham A, Achiron R.Determination of fetal occiput position by ultrasound duringthe second stage of labor. J Matern Fetal Neonatal Med2001;10: 283286.



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5. Sherer DM, Miodovnik M, Bradley KS, Langer O. Intrapartumfetal head position II: comparison between transvaginal digitalexamination and transabdominal ultrasound assessment duringthe second stage of labor. Ultrasound Obstet Gynecol2002;19: 264268.

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7. Rane SM, Guirgis RR, Higgins B, Nicolaides KH. Thevalue of ultrasound in the prediction of successfulinduction of labor. Ultrasound Obstet Gynecol 2004;(in press).

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Ultrasonographic occiput position in early labour in theprediction of Caesarean section. BJOGDOI: 10.1111/j.1471-0528.2004.00134.x.

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