Validity of bladder volume measurement by ultrasound in women postpartum

Vaginal birth increases the risk of urinary retention and overdistention of the bladder. To avoid unnecessary discomfort by catheterization, it is preferable to use ultrasound for diagnosis of these conditions. The aim of this study was to determine the validity of transabdominal ultrasound and a portable ultrasound system, Biocon-700, to measure bladder volume in women postpartum.

Fifty women were included in this method comparison study. Within 48 h of giving birth, their bladder volume was measured in randomized order with both transabdominal ultrasound and Biocon-700. After urination, participants were scanned with Biocon-700 to measure residual bladder volume, and finally the bladder was emptied by catheterization. The total bladder volume was calculated as the voided volume plus the catheterized volume.

Biocon-700 measured 43.4 ml ± 117.4 ml (mean ± SD) lower than the total bladder volume, while volumes measured by transabdominal ultrasound were 117.8 ml ± 110.0 ml (mean ± SD) lower. Linear regression showed significant proportional bias in both methods. The Biocon-700 could detect a residual bladder volume > 150 ml with a positive predictive value of 66.7% and a negative predictive value of 100%.

Neither transabdominal ultrasound nor the portable ultrasound system, Biocon-700, can be used to measure bladder volume precisely after vaginal delivery. However, both ultrasound methods can be used as screening tools to prevent overdistention of the bladder, and Biocon-700 can furthermore be used to screen women for a residual bladder volume > 150 ml.