Is urethral pressure associated with parity and delivery mode?

Introduction and hypothesis: Stress urinary incontinence is the most prevalent type of urinary incontinence and childbirth is a risk factor. The aim of this study is to evaluate the association between delivery mode and urethral sphincter function as measured by the maximum urethral pressure (MUP). Methods: A retrospective study on women seen in a tertiary urogynaecological center for urodynamic testing between January 2017 to December 2019. Women were classified into the following groups: (1) nulliparous; (2) caesarean section only; (3) at least one spontaneous vaginal delivery but no instrumental deliveries; (4) at least one vacuum delivery but no forceps; (5) at least one forceps delivery. Results: The complete data sets of 1238 women were analysed; 1112 (90%) were vaginally parous. Mean age was 58 (18–95) years. Mean parity was 2.6 (0–9); 57 (4.6%) were nulliparous, 69 (5.6%) had only been delivered by caesarean section, 762 (61.6%) had at least one spontaneous vaginal delivery but no instrumental deliveries, 41 (3.3%) had at least one vacuum but no forceps delivery, and 309 (25%) had at least one forceps delivery. Mean MUP was 41.8 cmH₂O. There was a significant association between vaginal parity and MUP (P < 0.001). On ANOVA test, delivery mode was significantly associated with MUP. This became nonsignificant on regression analysis, with only age significantly associated with MUP (P < 0.001). Conclusions: The effect of childbirth on urethral sphincter function seems to be largely due to the first vaginal birth. We failed to show an effect of instrumental delivery.