Postvoid residual volumes (PVRV) in the postpartum period are poorly studied and a cut-off value to diagnose postpartum urinary retention (PPUR) is not well-defined. Most studies and guidelines use a PVRV of 150 ml to diagnose PPUR. [1] Asymptomatic patients are classified as “covert” PPUR, and those with symptoms of incomplete voiding as “overt” PPUR.  One recent study has shown that mean PVRV after vaginal delivery might be higher than the cut-off of 150 ml. [2] To this date, no study has compared the distributions of PVRV after vaginal delivery with PVRV after cesarean section.
This study aims to investigate the distribution of PVRV in postpartum women and to compare PVRV after vaginal delivery and cesarean section.

This was a prospective observational study in a tertiary academic hospital about postvoid residual volumes after delivery. Inclusion criteria: age ≥ 18 years of age at date of delivery, delivery at the study site, and written informed consent. Exclusion criteria: lack of consent and “overt” PPUR. 
All measurements were done in the first 24 hours after delivery or the removal of an indwelling catheters. Measurements were performed by bladder scan and/or transabdominal ultrasound in the 15 minutes after micturition. Those with PVRV ≥ 150 ml but normal micturition quantities (at least 200 ml), serial ultrasound scans were proposed during the hospital stay.
Women were asked to answer the section about bladder function of the adapted version of the German pelvic floor questionnaire to evaluate bladder symptoms in the four weeks prior to delivery. [3]
Descriptive statistics were performed using contingency tables with absolute and relative distribution for categorial variable with mean and standard deviation or median and interquartile ranges for continuous variables. Secondary endpoints were analyzed using Chi-Square-test/Fisher-exact-test (categorial variables) and Mann-Whitney U-test/Kruskal-Wallis-test (continuous variables). 
Four arbitrary cut-offs to investigate risk factors were chosen prior to analysis: 150 ml (cut-off for PPUR), 250 ml (cut-off in a recent study [2]), the 75th percentile and the 95th percentile of PVRV. Risk factors were calculated using univariate and multivariate regression analysis. Associations between potential predictors and outcome are reported as odds ratios with 95% confidence intervals.

A total of 105 patients were included in the study with 57 in the vaginal delivery-group and 48 in the cesarean section group. Seven women (7%) in the vaginal delivery group developed overt PPUR and were therefore not included in the final analysis.  No differences for age, BMI and parity were found between the groups. 
Mean postpartum postvoid residual volume was 153 ml, and no differences between both groups were found (173 vs 133 ml; p = 0.15). The 75th percentile was 211 ml and the 95th percentile 464 ml, respectively. In total, 39% of women (39/98) had PVRV ≥ 150 ml and 21% (21/98) even ≥ 250 ml. In women with vaginal delivery 44% (22/50) had PVRV > 150 ml, and in women with cesarean section 35% (17/48) had PVRV ≥ 150 ml (p = 0.39). (see fig. 1)
Incomplete voiding was significantly associated with PVRV above the four cut-offs (p = 0.008 for PVRV ≥ 150ml, and p < 0.001 for PVRV ≥ 250ml, ≥75th percentile, and ≥ 95th percentile, resp.). Nevertheless, 25% of all women with complaints of incomplete voiding had PVRV ≤ 150 ml. The other 75% had mean micturition volumes of 474 ml, showing no difference to women without voiding difficulties. In the follow-up of the 39 women with PVRV ≥ 150 ml, 15 women were available for control scans, with 40% having PVRV below 150 ml at the second or third scan. No patient had symptomatic urinary retention at hospital discharge and no complications due to increased PVRV were found.
In multivariate analysis, no risk factors for any of the PVRV cut-offs could be identified. 
58% of all participants answered the German pelvic floor questionnaire. Women with a reduced quality of life and those who suffered from bladder symptoms prior to delivery had significantly higher scores (3.2 vs 1.3; p < 0.001 and 3.0 vs 1.0; p < 0.001, resp.). No association was found between these two groups and increased PVRV or feeling of incomplete voiding after delivery. Prior to delivery, 23% of respondents complained of incomplete voiding, with only three of these (23%) having a persistence of symptoms after delivery (p = 0.09) with only one having presented a PVRV ≥ 150 ml. No association was found between women who presented subjective incomplete voiding prior to delivery and increased PVRV or subjective incomplete voiding after delivery, respectively.

In this study, first postpartum postvoid residual volumes did not seem to differ between the two types of delivery. Nevertheless, after vaginal delivery, almost half of the women had PVRV ≥ 150 ml. Even after cesarean section, more than a third had PVRV ≥ 150 ml. While incomplete voiding is associated with increased PVRV, most women had still high micturition volumes. Additionally, most women normalize their PVRV before hospital discharge without the need for any intervention. Still, 7% of all women had overt PPUR with an impossibility to void and had to be excluded from the study. 
Like another study group, we found mean postpartum PVRV to be ≥ 150 ml. [2] In our study, we also investigated women after cesarean section. Based on the results of the two studies, it might be advisable to re-evaluate the current cut-off for covert PPUR. Evidently, our study does not show an absence of long term problems, but we showed that most women with increased PVRV normalize their PVRV during the following days, and this makes long term consequences rather unlikely. 
No risk factors were identified but this could be due to the number of participants in each group. Although incomplete voiding is not infrequent before delivery, we found no association with voiding difficulties in the postpartum period. Incomplete voiding was well associated with PVRV ≥ 150 ml or more and might be sufficient to identify patients at risk of increased PVRV.

The current cut-off value of 150 ml to define postpartum urinary retention is lower than the mean postvoid residual volume in this study. This is the second study that shows mean postpartum PVRV ≥ 150 ml. [2] To avoid unnecessary treatments in postpartum women, a higher cut-off value than 150 ml to diagnose PPUR seems advisable. Most women’s PVRV return to normal before hospital discharge without any intervention.

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Mulder FEM, Rengerink KO, van der Post JAM, Hakvoort RA, Roovers J-PWR. Delivery-related risk factors for covert postpartum urinary retention after vaginal delivery. Int Urogynecology J. 2016  Jan;27(1):55–60.
Metz M, Junginger B, Henrich W, Baeßler K. Development and Validation of a Questionnaire for the Assessment of Pelvic Floor Disorders and Their Risk Factors During Pregnancy and Post Partum. Geburtshilfe Frauenheilkd. 2017 Apr 26;77(04):358–65.

Continence 2S2 (2022) 100259
DOI: 10.1016/j.cont.2022.100259