The abdominal circumference(AC) is the single most important measurement in assessing fetal size and growth. It is also a mandatory measurement.
Severe intrauterine growth retardation can be missed if the AC is not measured.
Measurement of the AC should be made as accurately as possible. The best plane is the one in which the portal vein is visualized in a tangential section. The plane in which the stomach is visualized is also acceptable. The outer edge of the circumference is measured. Track-balls, light-pens etc. can all be used. On screen computer-generated elliptical measurements probably yield the best results. 2-diameters equations and manual on-screen traces are less accurate and should best be avoided. If serial measurements are performed, it will not be difficult to smooth out the irregularities and come to very fine projections of the AC.
With a good AC, one will be able to arrive at a very accurate fetal weight, the cornerstone in the assessment of intrauterine fetal growth.