Pelvic floor parameters predict postpartum stress urinary incontinence: a prospective MRI study

Abstract

Objective: To investigate the pelvic floor changes in primiparas with postpartum stress urinary incontinence (SUI) after vaginal delivery using pelvic floor MRI.

Materials and methods: Fifty-two women were enrolled in the primiparous stress urinary incontinent (PSUI) group and 51 in the primiparous continent (PC) group. Thirty nulliparas were also recruited as the nulliparous control (NC) group. Levator ani muscle (LAM) injury, levator hiatus area (LHA), H-line, M-line, the distance from the bladder neck and cervix to the pubococcygeal line (B-PCL and U-PCL), levator plate angle, the anterior angle of the urethra, bladder neck descent, retrovesicourethral angle, functional urethral length, and a bladder neck funnel were evaluated on MRI images. Univariate and multivariate logistic regression analyses were used to explore anatomical predictors for SUI.

Results: The primiparas in the PSUI group showed more obvious LAM injuries than in the PC groups (p = 0.001). LAM function assessment: the PSUI group had larger LHA and shorter B-PCL and U-PCL than the other groups during straining. Assessment of urethral mobility and function: the PSUI group had larger anterior angle of the urethra, bladder neck descent, retrovesicourethral angle, and shorter functional urethral length than the other two groups (all p < 0.05). Up to 88.5% of primiparas in the PSUI group showed bladder funnel (p < 0.001). The logistic regression analysis showed that retrovesicourethral angle, functional urethral length, and the presence of bladder funnel were significantly associated with postpartum SUI (p < 0.05).

Conclusions: Increased retrovesicourethral angle, shortened functional urethral length, and the presence of bladder funnel may be anatomical predictors for SUI in the early postpartum period. Urethral sphincter dysfunction plays an essential role in developing postpartum SUI.

Critical relevance statement: This study used several measurements to reflect the anatomical structure and functional changes of the pelvic floor to identify the best anatomical predictors associated with postpartum stress urinary incontinence (SUI), aiming to provide new insights into treatment strategies for postpartum SUI.

Key points: • Increased retrovesicourethral angle, shortened functional urethral length, and the presence of bladder funnel are more commonly seen in primiparas with SUI. • The combination of retrovesicourethral angle, functional urethral length, and bladder funnel had the highest diagnostic performance in predicting postpartum SUI (AUC=0.947). • Urethral sphincter dysfunction may be the main pathophysiological foundation in SUI development.

Keywords: Magnetic resonance imaging; Pelvic floor; Pelvic floor dysfunction; Stress urinary incontinence; Vaginal delivery.

Fig. 1

Flowchart of patient selection. PSUI group, primiparous stress urinary incontinent group; PC group, primiparous continent group

Fig. 2

Axial T2-weighted images were performed to assess levator ani injury. The diagnosis of abnormal muscle was based on muscle swelling and defect. a 0 = normal, b 1 = less than half abnormality of the muscle, c 2 = more than half abnormality of the muscle, d 3 = total or near-total loss of the muscle

Fig. 3

Schematic diagram of pelvic floor measurements. a Axial T2-weighted images. LHA, levator hiatus area. b–f Median sagittal T2-weighted images. H line, puborectal hiatus line; M line, muscular pelvic floor relaxation line; B-PCL, bladder-pubococcygeal line; U-PCL, uterus-pubococcygeal line; FUL, functional urethral length; LPA, levator plate angle; AUA, anterior angle of the urethra; RVA, retrovesicourethral angle; all the parameters were measured at rest and straining respectively; h, i bladder neck descent is defined as the difference in distance from the bladder neck to the PCL line at rest and straining. Negative value was taken if the bladder neck was located below PCL. j, incomplete bladder neck closure in a primiparous incontinent woman manifested as bladder neck funnel (arrows)

Fig. 4

Prism plot for comparison of morphology and function of the levator ani muscle. a–f The comparison of each pelvic floor parameter at rest; g–l the comparison of each pelvic floor parameter during straining; m the constituent ratio of LAM injury between the three groups. LPA, levator plate angle; * represents p < 0.05, ** represents p < 0.001

Fig. 5

Prism plot for comparison of urethral mobility and urethral sphincter function. a–c The comparison of each pelvic floor parameter at rest; e–g the comparison of each pelvic floor parameter during straining; d the descent distance of the bladder neck during the Valsalva maneuver; h the constituent ratio of the bladder funnel between the three groups. AUA, anterior angle of the urethra; RVA, retrovesicourethral angle; FUL, functional urethral length; BND, bladder neck descent; * represents p < 0.05, ** represents p < 0.001

Fig. 6

ROC curve of pelvic floor parameters for predicting postpartum SUI. FUL-S, functional urethral length; RVA-S, retrovesicourethral angle; both were measured during straining