Intrapartum ultrasound for cervical dilatation: Inter- and intra-observer agreement.

INTRODUCTION: Digital vaginal examination (DVE) is considered the standard of care for assessing labor progress and cervical dilatation. However, it may be painful and is a subjective method that can increase the risk of chorioamnionitis. Known inter- and intra-observer variability exists in measurements of cervical dilatation obtained digitally. However, little is known about the inter- and intra-observer variability when using intrapartum transperineal ultrasound (TPUS). Our objectives were to investigate the relationship between cervical dilatation as assessed by TPUS and DVE. To assess inter- and intra-observer variability in both single and repeated ultrasound assessments of cervical dilatation during active labor. MATERIAL AND METHODS: This single-center study was conducted at an inner-city maternity unit in London, UK. Nulliparous participants at term with a live, singleton fetus in cephalic presentation were recruited between May 2021 and November 2022. During active labor, TPUS was performed subsequent to DVE. Repeat ultrasound assessments were performed where feasible. Participants were in a supine position, with flexed hips and knees and with an empty bladder. The ultrasound transducer was placed transversely on the maternal perineum. The anteroposterior (AP) diameter of the cervix was measured, and two-dimensional (2D) cine-loop videos were analyzed to obtain accurate measurements. Data were excluded if the time difference between DVE and TPUS exceeded 60 min. RESULTS: Of the 206 participants who consented to the study, complete data were obtained from 110 participants, yielding 147 paired TPUS and DVE observations. Ninety-six participants were excluded. The absolute difference between TPUS and DVE assessments was 0 cm in 34% of the observations, 1 cm in 46.3%, and between 2 and 4 cm in 19.7%. The mean difference was -0.9 cm (intraclass correlation coefficient = 0.85; p < 0.001). Data from 30 participants, with 50 cervical dilatation measurements, were used to assess inter- and intra-observer variability. The mean difference for the first ultrasound assessment was 0.07 cm (95% limit of agreement = -0.96 to 1.10, p < 0.001), for inter-observer variability, and 0.01 cm (95% limit of agreement = -0.29 to 0.30; p < 0.001) for intra-observer variability. CONCLUSIONS: Assessment of the cervix with TPUS during active labor is feasible and shows a strong correlation with DVE measurements. The majority of ultrasound measurements yielded readings within 1 cm of the corresponding DVE values, demonstrating high intraclass correlation and good inter- and intra-observer agreement.

The sonopartogram.

The assessment of labor progress from digital vaginal examination has remained largely unchanged for at least a century, despite the current major advances in maternal and perinatal care. Although inconsistently reproducible, the findings from digital vaginal examination are customarily plotted manually on a partogram, which is composed of a graphical representation of labor, together with maternal and fetal observations. The partogram has been developed to aid recognition of failure to labor progress and guide management-specific obstetrical intervention. In the last decade, the use of ultrasound in the delivery room has increased with the advent of more powerful, portable ultrasound machines that have become more readily available for use. Although ultrasound in intrapartum practice is predominantly used for acute management, an ultrasound-based partogram, a sonopartogram, might represent an objective tool for the graphical representation of labor. Demonstrating greater accuracy for fetal head position and more objectivity in the assessment of fetal head station, it could be considered complementary to traditional clinical assessment. The development of the sonopartogram concept would require further undertaking of serial measurements. Advocates of ultrasound will concede that its use has yet to demonstrate a difference in obstetrical and neonatal morbidity in the context of the management of labor and delivery. Taking a step beyond the descriptive graphical representation of labor progress is the question of whether a specific combination of clinical and demographic parameters might be used to inform knowledge of labor outcomes. Intrapartum cesarean deliveries and deliveries assisted by forceps and vacuum are all associated with a heightened risk of maternal and perinatal adverse outcomes. Although these outcomes cannot be precisely predicted, many known risk factors exist. Malposition and high station of the fetal head, short maternal stature, and other factors, such as caput succedaneum, are all implicated in operative delivery; however, the contribution of individual parameters based on clinical and ultrasound assessments has not been quantified. Individualized risk prediction models, including maternal characteristics and ultrasound findings, are increasingly used in women's health-for example, in preeclampsia or trisomy screening. Similarly, intrapartum cesarean delivery models have been developed with good prognostic ability in specifically selected populations. For intrapartum ultrasound to be of prognostic value, robust, externally validated prediction models for labor outcome would inform delivery management and allow shared decision-making with parents.