1. UOG Journal Club: March 2012
Agreement between two- and three-dimensional transperineal ultrasound methods in assessing fetal head descent in the first stage of labor
E. 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)

2. Background
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

3. Objective: to study intraobserver repeatability and
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
Objective: to study intraobserver repeatability and
intermethod agreement between 2D and 3D ultrasound in
assessing fetal head descent during the first stage of labor

4. Two transperineal ultrasound (TPU) parameters
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
Two transperineal ultrasound (TPU) parameters
were 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
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

5. (one volume acquired and analyzed later 3 times for each parameter)
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

6. 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
Intraobserver repeatability
Intermethod agreement (2D–3D)
Was expressed as:
the difference between the highest and lowest measurements
the intraclass correlation coefficient (ICC)
the repeatability coefficient (the range within which two measurements by the same observer will fall for 95% of subjects)
Was performed using:
the mean of 3 measurements for each technique
Intermethod agreement was expressed using the two-way random effects ICC
Cohen’s kappa was used to assess agreement for categorical data
In addition, linear regression analysis was performed to investigate the
association between angle of progression and fetal head–perineum distance
(expressed using the Pearson correlation coefficient – “r”) 6

7. Results: Intraobserver repeatability Repeatability coefficient (mm)
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
Results: Intraobserver repeatability
Fetal head–perineum distance 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)
Angle of Progression 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)
ICC, intraclass correlation coefficient

8. 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
Results: Intermethod agreement
Fetal head–perineum distance
Angle of progression
ICC (95% CI)
0.95 (0.93–0.97)
0.93 (0.89–0.95)
Intermethod 95% limits
of 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 *
( )
0.79 †
( )
ICC, intraclass correlation coefficient
* Using 40 mm as a cut-off level
† Using 110º as a cut-off level 8

9. 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
Results: Bland–Altman plots of intermethod agreement between 2D and 3D measurements
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.

10. 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
Results: Association between angle of progression and fetal head–perineum distance
2D: r=−0.72
The association was significant at the 0.01 level for both the 2D (r=0.72) and 3D (r=0.71) scan methods
r = Pearson correlation coefficient

11. 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
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

12. Strength of the study Weakness
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
Strength of the study
Inclusion of a large, homogeneous and well-defined population
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 12

13. 2D and 3D ultrasound methods might be used interchangeably
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 13