Figure 2: Sagittal abdominal diameter (SAD) measurement and Inter-observer agreement
(a) Vertical white arrow shows sagittal abdominal diameter (SAD) measurement: the largest skin-to-skin distance perpendicular to the table. Arrowhead (yellow) indicates anatomical landmarks for each location: the umbilicus, the left emerging renal vein, and the emerging inferior mesenteric artery.
(b) SAD values of observer A vs observer B for each corresponding measurement. The continuous line of equality (y=x) represents perfect concordance. The discontinuous line represents the relationship between the 2 readings. Umbilical SAD measurements are the most similar to the line of equality. In the left renal vein and inferior mesenteric artery measurements, the lines are almost parallel to the reference line, indicating a possible systematic error.
(c) Bland-Altman plots to compare agreement. Difference between the two measurements: the continuous line represents perfect agreement (Obs. A − Obs. B = 0). The discontinuous line represents the mean difference between the 2 readings. The grey area defines the limits of agreement (95% confidence interval). The agreement was best for umbilical measurements as they are closest to the reference line. For the other SAD measurements, several readings were outside the limits of agreement. Systematic bias was ruled out since perfect agreement (y=0) was within the confidence interval.