Ultrasound diagnosis of fetal head engagement

    Ultrasound diagnosis of fetal head engagement Kaouther Dimassi, Anissa Ben Amor, Cyrine Belghith, Mohamed Amine Ben Khedija, Amel Triki, Mohamed Faouzi Gara PII: DOI: Reference:

S0020-7292(14)00290-2 doi: 10.1016/j.ijgo.2014.04.008 IJG 7991

To appear in:

International Journal of Gynecology and Obstetrics

Received date: Revised date: Accepted date:

5 January 2014 1 April 2014 22 May 2014

Please cite this article as: Dimassi Kaouther, Amor Anissa Ben, Belghith Cyrine, Khedija Mohamed Amine Ben, Triki Amel, Gara Mohamed Faouzi, Ultrasound diagnosis of fetal head engagement, International Journal of Gynecology and Obstetrics (2014), doi: 10.1016/j.ijgo.2014.04.008

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ACCEPTED MANUSCRIPT CLINICAL ARTICLE

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Ultrasound diagnosis of fetal head engagement

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Khedija a, Amel Triki a,b, Mohamed Faouzi Gara a,b

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Kaouther Dimassi a,b,*, Anissa Ben Amor a, Cyrine Belghith a, Mohamed Amine Ben

Obstetrics and Gynecology Unit, Mongi Slim Hospital, La Marsa, Tunisia

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Faculty of Medicine, University Tunis El Manar, Tunis, Tunisia

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* Corresponding author: Kaouther Dimassi

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Residence les Printemps 2, Bloc G, Appt 18, El Aouinia, 2045, Tunisia. Tel.: +216

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52550697; fax: +216 71885832.

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E-mail address: [email protected]

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Keywords: Digital examination; Engagement; Transperineal ultrasound

Synopsis: Measuring the perineum to fetal head distance via transperineal ultrasound was found to be a reliable method for the diagnosis of fetal head engagement.

ACCEPTED MANUSCRIPT ABSTRACT Objective: To compare clinical data and transperineal ultrasound results for the

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diagnosis of fetal head engagement.

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Methods: The present prospective longitudinal study enrolled 100 term women

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attending the Mongi Slim Hospital, La Marsa, Tunisia, between July and September 2012. The clinical assessment of fetal engagement was compared with ultrasound measurements. Ultrasound examination was performed in the delivery room. The

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probe was placed on the ano-vulvar area. The measure used was the distance

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between the perineum and external table of fetal skull. Results: The ultrasound measures of the perineum to external table of fetal skull

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ranged from 13 to 75 mm. The measures of the perineum to succedaneum bump

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ranged from 22 to 68 mm. A threshold of 55 mm was determined as the perineum to fetal head distance above which a diagnosis of engagement would be reversed. This

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proposed threshold had a positive predictive value of 98.6%, a sensitivity of 86.7%, and a specificity of 94.1%.

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Conclusion: Transperineal ultrasound is a simple, rapid, and reproducible method for the diagnosis of fetal head engagement. It can be used in the delivery room in addition to clinical examination and when the latter is hampered by a succedaneum bump.

ACCEPTED MANUSCRIPT 1. Introduction Engagement is the entrance of the fetal presenting part into the superior pelvic strait

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and the beginning of the descent through the pelvic canal [1]. The possibility of

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natural delivery depends on this criterion. The digital vaginal examination (DVE)

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remains the “gold standard” for evaluating fetal station. This examination is relevant, but is known to be subjective and poorly reproducible [2,3]. Indeed, it is often

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inaccurate in the case of a succedaneum bump or an occipito-posterior position [4].

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Transperineal ultrasonography described in 2006 [5] might be useful in cases where there is clinical doubt about fetal engagement. The aim of the present study was to

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assess the use of transperineal ultrasonography in the diagnosis of fetal

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engagement and to compare the results with the findings from DVE.

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2. Materials and methods

The present prospective single-center preliminary study was conducted among

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pregnant women attending the Obstetrics and Gynecology Unit of Mongi Slim Hospital, La Marsa, Tunisia, between July 1 and September 30, 2012. The research protocol was approved by the hospital’s ethics committee .All participants gave informed consent and the data were analyzed anonymously.

The study included women with a singleton uncomplicated cephalic term pregnancy who were in the active phase of labor without contraindication to vaginal delivery, with a favorable Magnin index, and with no suspected fetal macrosomia.

ACCEPTED MANUSCRIPT The assessment of fetal head engagement (FHE) was performed for each patient at full dilation. The ultrasound examination was performed by one of the three residents

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involved in the study. A routine DVE was performed by an experienced midwife to

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assess fetal station via the Farabeuf sign. The midwife and resident carrying out the

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vaginal examination and ultrasound, respectively, were blind to the other result.

The ultrasound examination was performed in the labor ward among women at full

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dilatation with a ruptured amniotic sac and emptied bladder. The woman was placed

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in a classic gynecologic position with legs in supination. Two parameters were investigated: the fetal head position and the distance between the perineum and fetal

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head.

For the fetal head position, transabdominal ultrasonography was used to assess the

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orientation of fetal orbits, defined by the location of fetal cervical spine thorns and the occipital bone. The distance between the perineum and fetal head was measured by

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transperineal ultrasonography, in which the abdominal probe was placed perpendicular to the labia at the ano-vulvar area. The distance between the probe (p) and the external table of fetal skull (f) (Figure 1, dotted arrow) and that between the perineum (p) and the succedaneum bump (s) (Figure 2, full arrow) were measured. Thereafter, the ultrasound and DVE data were reported on the “patient” card by a third person.

Data were entered into Epi Info version 7 (CDC, Atlanta, GA, USA). Statistical analysis was performed with SPSS version 13.0 (SPSS Inc, Chicago, IL, USA). The t test and 2 test were used to compare quantitative and qualitative data, respectively.

ACCEPTED MANUSCRIPT The receiver operating curve (ROC) was used to determine a threshold for the perineum to fetal head distance above which the diagnosis of FHE would be

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reversed.

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3. Results

One hundred patients were enrolled during the study period. The mean age was 29.3 ± 4.6 years, the average weight was 72.8 ± 11.0 kg, and the average height

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was 1.6 ± 0.1 m. Ninety women (90.0%) had a body mass index (BMI, calculated as

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weight in kilograms divided by the square of height in meters) of more than 27; 51 women (51.0%) were primiparous; and four (4.0%) had previously delivered by

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cesarean.

The mean term was 39 weeks of gestation. The mean uterine height was

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31.6 ± 1.6 cm. The average period of active labor was 146.2 ± 92.9 min and the average period of FHE was 18.4 ± 9.5 min. Thirteen women (13.0%) had an

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operative vaginal delivery and six women had a cesarean delivery (6.0%). The fetal head position during expulsion was occipito-posterior for 93 women (93.0%). Lastly, the mean birth weight was 3462.8 ± 395 g.

The DVE performed at complete dilatation concluded that the fetal position was occipito-posterior in 10.0% of cases. The midwife had difficulty finding the fetal position in 12 women (12.0%). By contrast, the fetal position was determined in all patients by ultrasonographic examination, which recorded 97 occipito-anterior (97.0%) and 3 occipito-posterior (3.0%) positions.

ACCEPTED MANUSCRIPT The coefficient of agreement (Cohen  coefficient) between the clinical and ultrasound assessment of fetal head position was 83.5%. The failure of the DVE to

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assess correct fetal head position (17 cases, 17.0%) was usually linked to a

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head position were 85.0% and 95.6%, respectively.

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succedaneum bump. The sensitivity and specificity of DVE for the diagnosis of fetal

Regarding the assessment of FHE, DVE was doubtful in 21 women (21.0%) because

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of a large succedaneum bump. By contrast, the ultrasound examination was easy to

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perform on all patients. Ultrasound measurements ranged from 13 to 75 mm (mean 46.9 mm) for the p–f distance, and from 22 to 68 mm (mean 47.8 mm) for the p–s

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distance. Using the ROC curve, the threshold p–f distance, above which the

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diagnosis of engagement would be rejected, was 55 mm (Figure 3). On the basis of this threshold, the sensitivity and specificity of ultrasound for FHE diagnosis were

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86.7% and 94.1%, respectively. The positive predictive value and negative predictive

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value were 98.6% and 59.2%.

Figure 4 shows the distribution of ultrasound measurements according to the fetal head station. When the fetal head was considered “not engaged” by DVE, the p–f distance ranged from 52 to 75 mm (mean 64.9 ± 7.1 mm). For an engaged upper station (station 0/1), the p–f distance ranged from 42 to 65 mm (mean 55.4 ± 8.1 mm). For a middle station (station 2), the p–f distance ranged from 35– 58 mm (mean 44.7 ± 7.0 mm). Lastly, the p–f distance ranged from 13–45 mm (29.4 ± 8.5 mm) for a bottom station (station 3/4).

ACCEPTED MANUSCRIPT The transperineal ultrasonography visualized a succedaneum bump in 40 cases (40.0%), the height of which ranged from 2 to 32 mm (mean 8 mm). For 11 patients

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with a succedaneum bump, DVE had concluded an engaged presentation; the p–f

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distance was greater than 65 mm for two of these patients and greater than 55 mm

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for the other nine.

4. Discussion

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The assessment of fetal head station in labor is based on the relationship between

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the leading edge of the fetal head and maternal ischial spines. Although several clinical signs have been described for the diagnosis of engagement, the validity of

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these signs is not documented. Moreover, all of these signs can be misinterpreted in

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cases of a succedaneum bump, an occipito-posterior position, or a high BMI. For instance, the reliability of DVE to determine fetal engagement is 88% even among

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experienced clinicians [3], reflecting how difficult and unreliable this clinical evaluation can be. Similarly, the simulator study of Dupuis et al. [6] showed that the

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DVE of fetal head station is unreliable (50–88% error among residents, and 36–80% among seniors).

The failures of DVE are usually related to the non-exceptional presence of a succedaneum bump during labor [4], as observed in the present study, where the height of the bump was up to 32 mm. The situation is more complicated when an incorrect DVE diagnosis of fetal position or station leads to wrong positioning of the forceps with significant consequences for the fetus [7].

ACCEPTED MANUSCRIPT As a result, a more objective method for assessing FHE is needed in labor wards. Ultrasound imaging has been reported as an adjunctive method for evaluating fetal

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progression in the maternal pelvis. For example, transabdominal ultrasonography is

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now well known as a simple, accurate, and reproducible method for evaluating fetal

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position [8–13]. However, the use of ultrasound for diagnosing FHE is less common [7,14–18].

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Ultrasound diagnosis of FHE can be performed by either a translabial [17–20] or

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transperineal [5,14,17,18,21,22] approach. In addition, ultrasound measurements can be made via linear or angular methods. In all of these methods, the main

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anatomic landmarks are the pubis symphysis and the outer table of the fetal skull.

Dietz and Lanzarone [19] described the translabial method, in which the ultrasound

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examination is performed from a strict sagittal plane. The bony landmarks used are the pubic symphysis and the most advanced edge of the fetal skull. The other

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reference is the urethra, which appears as a hypoechoic ductal image beneath the bladder. From the plane created by these references, the angle of progression of the fetal head is measured. For angles greater than 120°, progression was predictive of vaginal delivery in 90% of cases [21]. This method was not used in the present study, however, because the ultrasound device available in the labor ward did not make angular measurements and the method was considered difficult by the trainees, requiring both a learning curve and a measurement time of more than 2 minutes.

ACCEPTED MANUSCRIPT Instead, a transperineal examination with measurement of the p–f distance was used in the present study. This method is more accessible to residents, with an extremely

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short skill time of approximately 30 seconds. The results showed a good match

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between the ultrasound measurements and the fetal head position. Using the same

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technique, Maticot-Baptista et al. [14] highlighted the persistence of diagnostic doubt between “not engaged” and “station 0 engaged” presentation, where the range of values overlap. In addition, Raia-Barjat et al. [4] found a discordance of 3.6%

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between DVE and transperineal ultrasonography results for FHE diagnosis.

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Considering the progression of presentation in the birth canal, the discordance rate can reach 25%. Overall, however, determining the relevance of ultrasonography for

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the diagnosis of FHE seems difficult because the current “gold standard” is a clearly

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subjective and inaccurate DVE.

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Raia-Barjat et al. [4] took successful vaginal delivery as the primary endpoint and found that the average distance measured by ultrasound was higher for cesarean

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delivery than for vaginal delivery, but this result was not significant (49.3 mm vs 39.7 mm). When the distance was greater than 50 mm, however, the relative risk of cesarean delivery was 10.5. In the present study, the low frequency of a “non-event” (i.e. non-engagement) and instrumental delivery made such an assessment difficult.

The present study determined a threshold value for the p–f distance below which the diagnosis of engagement would be retained. A value of 55 mm had the best statistical characteristics with good sensitivity (86.7%) and a positive predictive value of 98.6%. Thus, if the p–f distance is lower than 55 mm, the fetal head would be diagnosed as engaged by this technique with a specificity of 94.1% and a negative

ACCEPTED MANUSCRIPT predictive value of 59.2%. Maticot-Baptista et al. [14] determined a threshold of 60 mm with a specificity of 89% and a negative predictive value of 94%; by contrast,

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Rivaux et al. [16] found that a threshold of 55 mm had the best features, with a

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sensitivity and negative predictive value of 100%, but a poor positive predictive value

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(29%). However, these two studies had a small number of cases and their results should be confirmed in a larger series.

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In summary, transperineal ultrasound was found to be a simple, rapid, and

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reproducible method for the diagnosis of fetal head engagement. It can be used in the delivery room in addition to clinical examination and when the latter is hampered

Conflict of interest

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by a succedaneum bump.

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The authors have no conflicts of interest.

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ACCEPTED MANUSCRIPT Figure 1 Ultrasound measurement of the distance between the probe and external table of fetal skull (p–f distance). Dotted line indicates the p–f distance; asterisk

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indicates the succedaneum bump; double asterisk indicates the fetal head.

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Figure 2 Ultrasound measurement of the distance between the perineum and

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succedaneum bump (p–s distance). Dotted line indicates the p–f distance; full line indicates the p–s distance; asterisk indicates the succedaneum bump; double asterisk indicates the fetal head.

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Figure 3 The threshold of the p–f distance for the diagnosis of fetal head

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engagement was 55 mm.

Figure 4 Distribution of ultrasound measurements (p–f distance) according to the

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fetal head station.

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