Is portable three-dimensional ultrasound a valid technique for measurement of postpartum urinary bladder volume?

To determine the accuracy of bladder volume (BV) measurement and to identify factors that influenced the ultrasound bladder scanner (UBS) measurement of BV in postpartum women compared with transurethral catheterization.

A total of 190 paired measurements were performed on 190 women aged between 16 and 47 years. Majority of the women (36.9%) were in their first parity (range: 1-9). The mean BV was 159.46 mL [standard deviation (SD) = 99.78; range: 17-593 mL] on three-dimensional (3D) UBS and 143.76 mL (SD = 104.89; range: 2-588 mL) on catheterization. The mean difference between the two values was 15.70 mL (SD = 69.31, p < 0.001). The Foley's catheter was clamped for a minimum of 30 minutes and a maximum of 260 minutes. The UBS measurements were highly correlated with the BV obtained by catheterization (r = 0.819; p < 0.001). There was no significant difference between UBS and catheterized volume in a different volume subgroup. There were 35 cases (18.2%) with the difference in measurement of more than 25%. Twenty-five cases were associated with a catheterized volume less than 50 mL. There were a total of 33 cases with true BV of less than 50 mL, and only eight cases (24.24%) had an accurate measurement. The UBS tends to overestimate BV between 2 and 270 mL in this group. There was a significant linear relationship between the difference in measurement and body weight and duration of clamping.

Measurement of BV in immediate postpartum period using UBS is comparable with urethral catheterization. The accuracy of measurement is affected by body weight and increasing amount of BV.