UOG Journal Club: March 2012Agreement between two- and three-dimensional transperineal ultrasound

methods in assessing fetal head descent in the first stage of laborE. A. Torkildsen, K. Å. Salvesen and T. M. Eggebø

Volume 39, Issue 3, Date: March 2012, pages 310–315

Journal Club slides prepared by Dr Aly Youssef(UOG Editor for Trainees)

Transperineal ultrasound (TPU) can assess fetal head descent before and during labor

The literature is sparse on this subject, and there is no agreement regarding the superiority of 3D versus 2D ultrasound to assess fetal head descent

Although 2D and 3D transperineal ultrasound in the labor ward are reproducible and repeatable techniques, the intermethod agreement between 2D and 3D techniques has not been investigated

Background

Objective: to study intraobserver repeatability and

intermethod agreement between 2D and 3D ultrasound in

assessing fetal head descent during the first stage of labor

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

Torkildsen et al., UOG 2012

Angle of progression(Barbera UOG 2009)

• The angle between the pubic symphysis and a line tangential to the fetal skull • Assessed in a mid-sagittal view

Two transperineal ultrasound (TPU) parameterswere assessed in the study

Head–perineum distance(Eggebø UOG 2006)

• The shortest distance between the outer limit of the fetal skull and the perineum • Assessed in a transverse view

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

Torkildsen et al., UOG 2012

Patients and Methods• 106 primiparous women with a live singleton term fetus in cephalic presentation and a

diagnosis of prolonged first stage were included in the study• Women were examined in the lithotomy position, with empty bladder, after rupture of

membranes and between contractions

For each woman both the “angle of progression” and “fetal head–perineum distance” were assessed using two different methods of acquisition

2D

(3 acquisitions)

3D (one volume acquired and analyzed later 3

times for each parameter)

• All volumes and images were obtained and stored by one operator without measured values, and all 2D and 3D measurements were later performed by another operator blinded to clinical assessment and labor outcome

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

Torkildsen et al., UOG 2012

Statistical analysis

Was expressed as: 1. the difference between the highest and

lowest measurements2. the intraclass correlation coefficient

(ICC) 3. the repeatability coefficient (the range

within which two measurements by the same observer will fall for 95% of subjects)

Intraobserver repeatability Intermethod agreement (2D–3D)

Was performed using:1. the mean of 3 measurements for each

technique2. Intermethod agreement was expressed using

the two-way random effects ICC3. Cohen’s kappa was used to assess agreement

for categorical data

In addition, linear regression analysis was performed to investigate theassociation between angle of progression and fetal head–perineum distance

(expressed using the Pearson correlation coefficient – “r”)

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

Torkildsen et al., UOG 2012

2D 3D

Mean measurement (mm) 40.1 39.3

Repeatability coefficient (mm)

± 4.1 ± 1.7

ICC (95% CI) 0.94 (0.92–0.96) 0.99 (0.99–1.00)

Results: Intraobserver repeatability

Fetal head–perineum distance

2D 3D

Mean measurement (º) 108.7 111.0

Repeatability coefficient (º) ± 6.7 ± 5.7

ICC (95% CI) 0.91 (0.87–0.93) 0.94 (0.91–0.96)

Angle of Progression

ICC, intraclass correlation coefficient

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

Torkildsen et al., UOG 2012

Fetal head–perineum distance Angle of progression

ICC (95% CI) 0.95 (0.93–0.97) 0.93 (0.89–0.95)

Intermethod 95% limitsof agreement

-5.8 to +7.2 mm -8.9º to 13.7º

Mean 2D–3D difference 0.7 mm 2.4º

Cohen’s kappa (95% CI) 0.85 *(0.75-0.95)

0.79 †(0.68-0.91)

ICC, intraclass correlation coefficient* Using 40 mm as a cut-off level† Using 110º as a cut-off level

Results: Intermethod agreement

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

Torkildsen et al., UOG 2012

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

Torkildsen et al., UOG 2012

angle of progression

There was a significant, albeit small, mean difference over the range of the measured values for both fetal head–perineum distance and angle of progression.

Results: Bland–Altman plots of intermethod agreement between 2D and 3D measurements

Results: Association between angle of progression and fetal head–perineum distance

2D: r=−0.72

r = Pearson correlation coefficient

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

Torkildsen et al., UOG 2012

The association was significant at the 0.01 level for both the 2D (r=0.72) and 3D (r=0.71) scan methods

• Both intraobserver repeatability and intermethod agreement between

2D and 3D acquisitions were good

• The results suggest that 2D and 3D ultrasound might be used interchangeably in fetal head descent assessment in labor

• The intraobserver repeatability was slightly better in 3D than 2D acquisitions

• The association between angle of progression and fetal head–perineum distance was good for both 2D and 3D ultrasound

Discussion

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

Torkildsen et al., UOG 2012

• Inclusion of a large, homogeneous and well-defined population

Strength of the study

Weakness• Variation in 2D measurements was analyzed using three different acquisitions,

while for 3D measurements the same acquired volume was uploaded three times

• Possible bias due to the performance of the 3D invariably after the 2D evaluation which might have been the reason of wider angle (mean difference 2.4º) and shorter distance (mean difference, 0.7 mm) in 3D measurements observed in the study. However, the differences were small and probably lacking clinical importance

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

Torkildsen et al., UOG 2012

Conclusion

• The intraobserver repeatability and agreement between 2D and 3D ultrasound assessment of fetal head descent in labor is good

• 2D and 3D ultrasound methods might be used interchangeably

• These results may not be applicable to the second stage of labor where further studies are necessary

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

Torkildsen et al., UOG 2012

• What are the advantages of ultrasound over digital examination for management of labor?

• What are the different ultrasound approaches that can be used to obtain images of the fetal head in labor?

• What are the different ultrasound measurements that can be taken to assess progress in labor?

• How useful are ultrasound methods in identifying fetal head position or predicting obstructed labor?

• What do the study findings suggest would be the simplest, most reproducible technique for assessing labor progress?

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

Torkildsen et al., UOG 2012

Discussion points

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