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Obstetric Ultrasound Scanning Technique
Harry Gee (teaching materials provided by David Cole, Lecturer at City University, Birmingham)
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2nd & 3rd Trimester Scans Identify fetus Placental site Biometry
Orientation Fetal heart beat Placental site Biometry Bi-Parietal Diameter (BPD) Head Circumference (HC) Abdominal Circumference (AC), Femur length (FL) Liquor Estimation 2
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2nd & 3rd Trimester Scans Place probe longitudinal on lower abdomen superior to symphysis pubis Slide probe superiorly using sweeping movements to locate fetus
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2nd & 3rd Trimester Scans Slide probe superiorly - sweeping side to side up to uterine fundus. 4
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FH + Orientation 5
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Fetal Orientation Lie Presentation longitudinal Transverse Oblique
cephalic breech
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Cephalic
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Breech
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Breech legs extended
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Transverse lie
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Placental localisation
Full bladder Midline sagittal section Placental position anterior or posterior Low placenta - measure distance between lower edge and internal os *
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Fundal placenta
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Major placenta praevia
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Minor placenta praevia
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Liquor volume Subjective assessment Maximum deepest pool (MPD)
Amniotic fluid index
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Subjective Assessment
Normal liquor volume
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Maximum deepest pool Deepest pool in cm
Do not include cord or fetal limbs
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Amniotic Fluid Index Sum of the deepest pools
in each of four quadrants
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Oligohydramnios MPD < 3 cm up to 36 weeks
MPD < 2 cm 36 weeks - term
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Polyhydramnios MPD > 8 cm
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Fetal Biometry Biparietal diameter BPD Head circumference HC
Abdominal circumference AC Femur length FL
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BPD Measurement ROCK 22
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Biparietal diameter BPD
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BPD Errors Few (best inter-observer error)
Oblique section (increases measurement) Not at BPD (decreases measurement)
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Head Circumference Trans-ventricular Plane
choroid plexus anterior horn posterior horn CSP falx cerebri
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Trans-ventricular Plane
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Measurement Criteria BPD & HC
Landmarks: CSP, Falx, thalami Alignment: symmetrical –midline no orbits, no cerebellum Calipers: BPD widest distance 90o midline. HC bony perimeter of skull
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Abdominal Circumference
Long Axis of fetus (Spine) Fetal trunk parallel to transducer Rotate transducer at right angles Move up and down until landmarks identified. Repeat to consistency
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Abdominal Circumference
spine Ao UV stomach
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Abdominal Circumference
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AC Sources of Error Oblique Section (Salami Effect) Too high Too low
Abdominal compression (oligo-hydramnios) Fetal Breathing
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FL Measurement Identify femur close to fetal bladder/pelvis.
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FL Measurement Slide probe so that femur is central
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FL Measurement Rotate probe to obtain full length image of femur.
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Femur Length 35
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Source of Error Oblique image (shortens measurement)
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The End
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