Inter‐ and intra‐observer agreement of <scp>2D</scp> and <scp>3D</scp> transperineal ultrasound of pelvic floor hiatal measurements in the second stage of labor

INTRODUCTION: Transperineal ultrasound has emerged as a reliable measure to monitor labor progress non-invasively. This sonographic method enables fetal head descent to be measured by determining the relationship of the fetal head to the maternal symphysis pubis and the fetal head in reference to the perineum. As the pelvic floor plays an important role in childbirth, measuring the levator hiatal dimensions may provide additional understanding of the mechanisms, particularly in the second stage of labor. MATERIAL AND METHODS: The objective was to assess both inter- and intra-observer agreement in measuring the levator hiatal dimensions at rest during the passive second stage of labor using two- and three-dimensional (2D, 3D) transperineal ultrasound. Women were prospectively recruited for ultrasound assessment in the second stage of labor. The study population consisted of nulliparous women at term (37 + 0-42 + 0 weeks' gestation) with a live singleton pregnancy. Study participants eligible for recruitment were approached in active labor and consented to participate in the "SONO-BIRTH" study. Transabdominal and transperineal ultrasound were performed following clinical assessments in labor. The 3D pelvic floor volumes were uploaded into the software to calculate the levator hiatal area (LHa), transverse hiatal diameter (TD), and the anteroposterior hiatal distance (APD). The quality of visualization from the 3D volumes of the symphysis pubis (SP), puborectalis (PR), and levator hiatus (LH) was scored between 0 and 2 (SP, PR) and 0-4 (LH) and was assessed by two independent observers. RESULTS: Of 95 participants consecutively recruited, 75 had ultrasound volumes available for assessment. The inter-observer agreement for APD in 3D was slightly better compared with APD in 2D measurements, the mean difference being -0.22 cm (intraclass correlation coefficient = 0.85; p < 0.001) and - 0.35 cm (intraclass correlation coefficient = 0.79; p < 0.001), respectively. Intra-observer agreement for APD in 2D demonstrated a mean difference of -0.03 cm (intraclass correlation coefficient = 0.91; p < 0.001). Image quality of 3D ultrasound volumes gave a Kappa score of 0.40 for SP and a Kappa score of 0.72 and 0.77, respectively, for PR and LH. CONCLUSIONS: Assessment of the levator hiatal dimensions in the second stage of labor using 2D and 3D ultrasound demonstrates good inter- and intra-observer agreement. Agreement between two operators for quality of imaging of the pelvic floor structures obtained from 3D imaging was lowest for the symphysis pubis and highest for the levator hiatus.