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)

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

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

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

(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

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

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

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 * (0.75-0.95) 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 8

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.

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

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

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

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