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Radiology
Intrapartum Ultrasound to Determine Birth Progress
Built from Obstetric Imaging
What’s inside
12 sections · 90 slides
Overview
- What this topic covers
Rationale and scope
What intrapartum ultrasound is, and the problem with the finger it supplements
- Definition of intrapartum ultrasound
- Limitations of digital vaginal examination
- Advantages of ultrasound over palpation
- Relation of ultrasound to clinical examination
- Traditional uses of ultrasound in labour
- Novel uses of ultrasound in labour
- Parameters measured by intrapartum ultrasound
- Transabdominal and transperineal approaches
Development of the technique
From A-mode tracings to a measurement mapped onto the palpation scale
- Ultrasound in labour during the 1990s
- Earliest reports of ultrasound for birth progress
- Landmark studies of 2006
- Angle of progression and the palpation scale
- Milestones in intrapartum ultrasound
- Current state of the field
Performing the examination
Where the probe goes, what it sees, and how the two scanning planes differ
- Transabdominal technique
- Transperineal technique: preparation
- Structures seen on a transperineal scan
- Maternal pelvic structures in the midline
- The two transperineal insonation planes
- Reading the median transperineal image
- Transducer placement and landmarks in the median plane
- Symphysis, fetal skull and caput on the median view
- Measuring head direction and head station
- Reading the transverse transperineal image
- Transducer placement and landmarks in the transverse plane
- Head-perineum distance and midline angle
Pelvic landmarks and dimensions
The bones the measurements are referenced to, and the pelvic dimensions ultrasound can add
- Bony landmarks used as references
- Female bony pelvis seen from above
- Distance between the ischial spines on cross-sectional imaging
- Subpubic arch angle
- Subpubic arch angle and mode of delivery
- Ultrasound measurement of the obstetric conjugate
Fetal head position
Which way the occiput faces, why the finger gets it wrong, and what the trial showed
- Definition of fetal head position
- Palpating fetal position and its errors
- Fetal skull sutures, fontanels and diameters
- Landmarks felt on vaginal examination
- Recommendations for ultrasound assessment of position
- Transabdominal assessment of head position
- Clock-face description of occiput position
- Transperineal assessment when the head is deep
- Occiput posterior position and its consequences
- Randomised trial of added ultrasound assessment
- Limits of the evidence on outcomes
Fetal head station
The most important marker of descent, and the three scales that describe it
- Definition of fetal head station
- Assessing station by palpation
- Advantages of measuring station by ultrasound
- Locating the level of the ischial spines on ultrasound
- Proxies used for head station
- Converting angle of progression to head station
- Conversion of Angle of Progression (AoP) to Head Station +− the Level of the Ischial Spines
- Conversion of Angle of Progression (AoP) to Head Station +− the Level of the Ischial Spines (continued)
- 0 cm
Head direction
A quick indirect marker that turns upward once the head is past the narrowest plane
- Definition of head direction
- Head direction during normal descent
- Change in head direction with descent
- The head up sign
- Head direction in occiput posterior labours
- Reading the head direction image
- Head direction and angle of progression on the median view
- Fetal head deep in the maternal pelvis
Head-perineum distance
The distance the head still has to cover, read straight through the perineum
- Definition of the head-perineum distance
- Technique for measuring head-perineum distance
- Relation of head-perineum distance to head station
- Strengths and limitations of head-perineum distance
Midline angle
Putting a number on rotation, not just descent
- Definition of the midline angle
- Midline angle and head station
Fetal head flexion
Why a tucked chin presents a smaller head, and how flexion is quantified
- Role of head flexion in labour
- Effect of head flexion on the presenting circumference
- Fetal skull diameters in profile
- Deflexion and hyperextension of the fetal head
- Occiput-spine angle
- Chin-to-chest angle
Current status and guidelines
What is endorsed, what performs best, and what has still to be agreed
- Why studies are difficult to compare
- Guidelines endorsing intrapartum ultrasound
- Questions still unsettled
- Best-performing markers in meta-analysis
- Traffic light algorithm for assisted vaginal birth
- Emerging and future uses
- Intrapartum ultrasound measurements at a glance
- Take-home points
- References
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- References (continued)
- Obstetric Imaging: Fetal Diagnosis and Care, 2nd Edition