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Obstetric Ultrasound Scanning Technique

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Presentation on theme: "Obstetric Ultrasound Scanning Technique"— Presentation transcript:

1 Obstetric Ultrasound Scanning Technique
Harry Gee (teaching materials provided by David Cole, Lecturer at City University, Birmingham)

2 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

3 2nd & 3rd Trimester Scans Place probe longitudinal on lower abdomen superior to symphysis pubis Slide probe superiorly using sweeping movements to locate fetus

4 2nd & 3rd Trimester Scans Slide probe superiorly - sweeping side to side up to uterine fundus. 4

5 FH + Orientation 5

6 Fetal Orientation Lie Presentation longitudinal Transverse Oblique
cephalic breech

7 Cephalic

8 Breech

9 Breech legs extended

10 Transverse lie

11 Placental localisation
Full bladder Midline sagittal section Placental position anterior or posterior Low placenta - measure distance between lower edge and internal os *

12 Fundal placenta

13 Major placenta praevia

14 Minor placenta praevia

15 Liquor volume Subjective assessment Maximum deepest pool (MPD)
Amniotic fluid index

16 Subjective Assessment
Normal liquor volume

17 Maximum deepest pool Deepest pool in cm
Do not include cord or fetal limbs

18 Amniotic Fluid Index Sum of the deepest pools
in each of four quadrants

19 Oligohydramnios MPD < 3 cm up to 36 weeks
MPD < 2 cm 36 weeks - term

20 Polyhydramnios MPD > 8 cm

21 Fetal Biometry Biparietal diameter BPD Head circumference HC
Abdominal circumference AC Femur length FL

22 BPD Measurement ROCK 22

23 Biparietal diameter BPD

24 BPD Errors Few (best inter-observer error)
Oblique section (increases measurement) Not at BPD (decreases measurement)

25 Head Circumference Trans-ventricular Plane
choroid plexus anterior horn posterior horn CSP falx cerebri

26 Trans-ventricular Plane

27 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

28 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

29 Abdominal Circumference
spine Ao UV stomach

30 Abdominal Circumference

31 AC Sources of Error Oblique Section (Salami Effect) Too high Too low
Abdominal compression (oligo-hydramnios) Fetal Breathing

32 FL Measurement Identify femur close to fetal bladder/pelvis.

33 FL Measurement Slide probe so that femur is central

34 FL Measurement Rotate probe to obtain full length image of femur.

35 Femur Length 35

36 Source of Error Oblique image (shortens measurement)

37 The End

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