Abdominal Circumference
Landmarks
- Transverse image of fetal abdomen.
- Umbilical portion of left portal vein within liver, as it meets the " pars transversa " (horizontal portion of left portal vein) seen as a right sided " L " or " C " shape.
- Fluid filled fetal stomach on the left.
- Fetal spine seen in cross section.
Measurement
- Trace along outer margin of abdomen with map measurer or an electronic digitizer.
- AP and transverse diameters measured outer to outer. Include subcutaneous tissue as fat deposition in the 3rd trimester can significantly increase AC.
Circumference = D1 + D2 x 1.57
- Image should be as round as possible (not ovoid). Avoid excessive pressure with the transducer on the fetal abdomen (this can distort the shape).
- If
shape is distorted electronic calipers should always be used to measure.
Abdominal Circumference (Tables / Graphs)
Variability
- Greatest variability of all parameters and is more acutely affected by growth disturbances than any other parameter.
|
12-18 wks |
+/- 1.9 wks |
Precision of predictors of Gestational
Age
Head circumference / Abdominal circumference ratio – Campbell
et.al. 1977
Head circumference / Abdominal circumference ratio – Campbell
et.al. 1977
