The influence of pregnancy, parity, and mode of delivery on urinary incontinence and prolapse surgery—a national register study

Abstract

The long-term effects of vaginal delivery, parity, and pregnancy on the pelvic floor remain uncertain and controversial issues. In comparison with studies using self-reported symptoms, surgical register data may offer a more valid means for evaluating the relative influence of these risk factors. This study used data from 3 high-quality nationwide registers, namely the Swedish National Quality Register of Gynecological Surgery, the Swedish Medical Birth Register, and the Total Population Register, to evaluate the contribution of vaginal and cesarean delivery, parity, and factors not related to childbirth to the long-term risk for reconstructive urogenital surgery. This was a register-based linkage study among women aged ≥45 years who underwent urinary incontinence or prolapse surgery from 2010 to 2017. This surgical cohort was divided into nulliparous women, women with ≥1 cesarean deliveries only, those with ≥1 vaginal deliveries, and according to the number of births. A corresponding reference group was constructed based on women born in 1960 from the Total Population Register (n=2,309,765). The Swedish Medical Birth Register was used to determine the rate of women with cesarean and vaginal delivery and their respective parity. Absolute and relative risk were presented per 1000 women with 95% confidence intervals. Pairwise differences were analyzed with Fisher exact tests and the Mann-Whitney U test for dichotomous and continuous variables. The trend between ≥3 ordered categories of dichotomous variables was analyzed with Mantel-Haenszel statistics. A total of 39,617 women underwent prolapse surgery and 20,488 underwent incontinence surgery. Among women with prolapse surgery, 97.8% had ≥1 vaginal delivery, 0.4% had ≥1 cesarean delivery only, and 1.9% were nullipara. Corresponding figures for those with incontinence surgery were 93.1%, 2.6%, and 4.3%, respectively. Women with vaginal deliveries were overrepresented in the prolapse surgery (relative risk, 1.23; 95% confidence interval, 1.22-1.24; P<.001) and incontinence surgery groups (relative risk, 1.17; 95% confidence interval, 1.15-1.19; P<.001). Nulliparous and cesarean delivered women were underrepresented in the prolapse surgery (relative risk, 0.14; 95% confidence interval, 0.13-0.15 and relative risk 0.055; 95% confidence interval, 0.046-0.065; all P<.001) and incontinence surgery groups (relative risk, 0.31; 95% confidence interval, 0.29-0.33 and relative risk, 0.40; 95% confidence interval, 0.36-0.43). The absolute risk for prolapse surgery was lowest after cesarean delivery (0.09 per 1000 women; 95% confidence interval, 0.08-0.11) and differed by a factor of 23 (absolute risk, 2.11 per 1000 women; 95% confidence interval, 2.09-2.13) from that after vaginal birth. The absolute risk for prolapse and incontinence surgery increased consistently with parity after vaginal births. This trend was not observed after cesarean delivery, which is on par with that of nulliparous women. The first vaginal birth contributed the highest increase in the absolute risk for pelvic organ prolapse surgery (6-fold) and stress urinary incontinence surgery (3-fold). The second vaginal birth contributed the lowest increase in the absolute risk for pelvic organ prolapse surgery (∼1/3 of the first vaginal birth) and for stress urinary incontinence surgery (∼1/10 of the first vaginal birth). Surgery for urinary incontinence and prolapse was almost exclusively related to vaginal parity. The risk for prolapse surgery increased consistently with parity after vaginal births but not after cesarean delivery, whereas the risk associated with cesarean delivery was on par with that of nulliparous women. Thus, cesarean delivery seems to offer protection from the need for pelvic organ prolapse and stress urinary incontinence surgery later in life.