Intrapartum Ultrasound Grand Challenge 2024

Over the years, global caesarian section (CS) rates have significantly increased from around 7% in 1990 to 21% today, surpassing the ideal acceptable CS rate which is around 10% to 15%, according to the World Health Organization (WHO). These trends are projected to continue increasing over the current decade, where both unmet needs and overuse are expected to coexist with the projected global rate of 29% by 2030. In light of this and concerns regarding adverse health and economic consequences following operative birth, there is increasing recognition that prevention of avoidable cesarean births is important, provided it does not increase rates of adverse neonatal or maternal outcomes.

Active management of labour has been proposed as a means of reducing unnecessary CSs. The WHO also issued guidelines on intrapartum care, which include a strong recommendation in favor of using a modified partograph and a recommendation of digital vaginal examination (VE) of the fetal head (FH) station every four hours during the first stage of labor. FH station is the level of the FH in the birth canal in relation to the imaginary line between the maternal ischial spines. The FH is considered to be engaged at station 0 when the leading part of the skull reaches this imaginary line. VE of the FH station has been demonstrated to be subjective, with a 30% to 34% error in classifying the FH station as highpelvis, midpelvis, lowpelvis, or outlet on a birth simulator with sensors by clinicians with varying experience. The majority of errors were caused by misdiagnosis of a midpelvic station for a true high-pelvic station, which, in real life, could mislead clinicians to perform a midcavity instrumental vaginal delivery when cesarean delivery might have been a better choice.

Accurate assessment of the FH station is crucial to ensure that childbirth proceeds normally, allowing for the early detection of any deviations from the anticipated course, enabling timely intervention to mitigate potential maternal or fetal complications. Compared with VE, an ultrasound examination, which allows visualization of the fetal structures and their relationship with maternal structures, is quite straightforward, and provides more objective and accurate results in assessing the FH station. It is neither time consuming nor causes discomfort of patient. The International Society of Ultrasound in Obstetrics and Gynecology has issued practical guidelines on intrapartum ultrasound in 2018 and recommended that an ultrasound assessment should be conducted when there is suspected delay or arrest of the first or second stage of labor or before considering assisted vaginal delivery. FH station is assessed by transperineal ultrasound using the maternal pubic symphysis (PS) or the perineum as landmark for reference of measurement. Of the various ultrasound parameters, angle of progression (AOP) and head symphysis distance (HSD) have been suggested as the reliable sonographic parameters to predict the outcome of the instrumental vaginal delivery. AOP is the angle between the long axis of the pubic bone and a line from the lowest edge of the pubis drawn tangentially to the deepest bony part of the fetal skull, whereas HSD is the distance between the lowermost edge of the pubic symphysis and the nearest point of the fetal head along a line perpendicular to the long axis of the pubic symphysis.

Despite its clear benefits, the implementation of intrapartum ultrasound in labor and delivery presents technical challenges. It is particularly worth mentioning that, different from antepartum ultrasound for professional sonographer in most obstetric examinations, intrapartum ultrasound is a relatively new technology for non ultrasound trained professionals to provide continuous 24h, on site, on demand labor and delivery services at the bedside. Moreover, labor is a dynamic process and multiple ultrasound examinations are done for assessing changes in FH station. Diagnostic accuracy is severely affected by subjective factors such as physician experience and fatigue. Undoubtedly, the availability of immediate and convenient diagnostic and intervention guided ultrasound support is required in the demanding labor and delivery environment.

The biomedical impact of this challenge is profound. Accurate and timely assessments can significantly reduce unnecessary CS rates, leading to better health outcomes for mothers and babies. Technically, this challenge calls for the development of automatic, user friendly systems for fetal biometrics, aiming to minimize intra and inter observer variability and enhance the reliability of measurements. Such advancements could revolutionize labor management, blending the precision of technology with the nuances of human care.