Intrapartum ultrasound stands poised to revolutionize the labor and delivery process, offering real-time and objective insights through fetal imaging into labor progress, where uncertainties have historically prevailed.
The accompanying video, featuring insights from Dr. Larry Hinkson, a leading obstetrician at Berlin's Charité Hospital, delves into the current applications of intrapartum ultrasound. Dr. Hinkson, a prolific researcher, is an expert on the use of intrapartum ultrasound to manage the second stage of labor, enhancing the safety of operative vaginal deliveries and reducing primary cesarean delivery rates.
Watch the full video HERE
New Advances in Intrapartum Ultrasound
Intrapartum ultrasound has a wide array of established and emerging uses, including traditional applications of fetal imaging and determining placenta location. The GE HealthCare Voluson™ platform has been adapted to quickly enable clinicians to obtain the data they need about labor progression to support clinical decision-making with the use of new features such as the SonoL&D tool on the Voluson SWIFT platform. With multiple patient examples and well-illustrated graphics, Dr. Hinkson clearly illustrates how clinicians can use the tool to swiftly obtain key measurements in an active labor and delivery unit to augment clinical decisions about mode of delivery. These measurements include the angle of progression (AoP), the head-to-perineum distance (HPD), and the midline angle (MA).
Angle of Progression and How to Measure it
Multiple studies over the past several years have shown that the AoP can be useful in the management of occiput posterior presentations as an indicator of the success and safety of operative vaginal delivery and the prediction of the length of the second stage of labor. AoP has also been associated with lowering the rate of cesarean delivery in select populations.
To measure the AoP, an image is acquired in the sagittal plane of the fetal skull, showing its relation to the pubic symphysis. A line is then drawn through the midline of the pubic symphysis (along its long axis), and then a second line is drawn from the lower edge of the pubic symphysis tangential to the presenting part, which is usually the fetal skull. The angle constructed between these two lines is the angle of progression.
Dr. Hinkson demonstrates the acquisition of this angle using the semi-automated SonoL&D tool, both while the uterus is at rest and while the patient pushes during a contraction. This allows the physician to quickly gain confidence about the potential success of an attempted operative vaginal delivery and communicate that to the patient during counseling and while obtaining consent. Patients can see clearly on the ultrasound screen the information gained from these measurements, helping them to make a truly informed decision.
SonoL&D Angle of Progression
SonoL&D Midline Angle Measurement
The Benefits and Potential of Intrapartum Ultrasound
With the same transperineal intrapartum ultrasound, Dr. Hinkson also obtains the head-to-perineum distance. With ultrasound, this measurement can be objectively measured to the fetal skull and avoids the uncertainty that exists with digital exams, particularly when a significant amount of fetal swelling or caput is present. With this measurement repeated alongside maternal pushing efforts, the clinician can clearly see whether progress is being made and gain confidence about the potential success of an operative delivery, if indicated.
Fetal caput or swelling can also make it very difficult to use traditional digital examination to determine the rotation of the fetal head. Knowledge of the exact rotation of the fetal head is a key element in safe operative vaginal deliveries. Dr. Hinkson demonstrates the technique of measuring the midline angle by drawing a line through the anterior to posterior dimension of the pelvis and then another line through the fetal sagittal suture. Once again, the SonoL&D tool semi-automates measurement of this angle—a task previously accomplished with a ruler and protractor on a printed ultrasound image. By repeating the measurement at rest and with pushing, the clinician can gain confidence by seeing this angle diminish, indicating proper rotation of the fetal head.
The video also demonstrates the "head up sign," which is seen when the fetal neck is extended and the head is directed upward in the pelvic outlet, another piece of evidence that a vaginal delivery or an operative vaginal delivery is likely to be successful. It also demonstrates another great clinical pearl: using transperineal ultrasound to observe coactivation of the perineal muscles while pushing. This finding has been associated with a longer second stage of labor and can help inform clinical decisions about the progress of pushing.
Intrapartum ultrasound also serves as an invaluable tool for the safe use of forceps, not just in predicting if a forceps delivery will be successful, but also in confirming the correct placement of the blades. Dr. Hinkson demonstrates how to use intrapartum ultrasound to correctly determine the fetal position, ensure that the maternal bladder is empty, look for the presence of a nuchal cord, and watch the placement of the forceps blades in real time to confirm correct placement.
He demonstrates using ultrasound to observe rotation of the fetal head with rotational forceps deliveries, and he discusses a study showing that ultrasound use during rotational forceps deliveries greatly enhanced safety for both the fetus and the mother.
The video concludes with a review of current guidelines for operative vaginal delivery from the Royal College of Obstetricians and Gynaecologists, which include the new 2020 recommendation that "ultrasound assessment of the fetal head position prior to assisted vaginal birth is recommended where uncertainty exists following clinical examination." This describes many cases where operative vaginal delivery is being considered, since molding of the fetal head makes traditional clinical examination uncertain and unreliable.
Ultrasound's Impact on Clinical Decision-Making and Safety in the Second Stage of Labor
In summary, Dr. Hinkson advocates for healthcare professionals to adhere to updated guidelines and incorporate ultrasound in certain instrumental deliveries. The video demonstrates the application of ultrasound during the delivery, providing objective visualization of the fetal head's position, forceps blade placement, and rotation of the fetal head, all of which are particularly useful in challenging cases. He underscores the significance of training, mentorship, and standardized protocols in achieving successful operative vaginal deliveries. The use of ultrasound during the labor and delivery process will revolutionize clinical decision-making during the second stage of labor, enhancing safety, improving communication with patients, and reducing the number of avoidable caesareans.
