Materials and Methods: This cross-sectional analytical study measured the post-void residual (PVR) urine volume by ultrasound, at most, 15 minutes after the first urination after delivery. Women with a PVR >150 mL without urinary symptoms were assigned to the postpartum covert urinary retention group. Data were analyzed with SPSS22. The chi-square and Mann-Whitney tests were used for quantitative and qualitative variables, respectively.

Results: In this study, 1120 patients had a normal delivery at Ayatollahs Rouhani hospital from 21 January 2016 to 20 January 2017. Of this number, 306 (29.4%) and 734 (70.6%) cases with and without urinary retention were allocated to the case and control groups, respectively. Women with instrumental delivery had 30.19 times (P = 0.003) higher odds of urinary retention. Instrumental delivery is one of the known risk factors of urinary retention. The linear effect of the total length of labor was also measured, and the results revealed that every one-minute increase in the total length of labor increases the odds of covert urinary retention by 1.008 times (P < 0.001).

Conclusions: The findings of the study showed that various factors are involved in the incidence of urinary retention. More precisely, instrumental delivery, birth weight, gestational age, and other factors can each be a risk factor for urinary retention.