Pregnancy and parturition negatively impact vaginal angle and alter expression of vaginal MMP-9

Parity is the greatest risk factor for the development of pelvic organ prolapse. The normally supported vagina is pulled up and back over the levator ani. Loss of vaginal angulation has been associated with prolapse and may represent injury to the vaginal supportive tissues. We proposed and examined the following hypotheses: (1) pregnancy and delivery impact vaginal support, leading to loss of vaginal angle; (2) vaginal angulation is restored postpartum; and (3) uncomplicated vaginal delivery (VD) is associated with accelerated remodeling of the vaginal fibrillar matrix. We prospectively enrolled a cohort of nulliparas in the first trimester of pregnancy, and abstracted demographic and delivery data. Metalloproteinase 9 (MMP-9) activity in the vagina was determined in the first and third trimesters and 1 year postpartum using a substrate activity assay. Uncomplicated VD was defined as none of the following: cesarean delivery, forceps or vacuum use, shoulder dystocia, obstetric anal sphincter laceration, or prolonged second-stage labor. Women were grouped dichotomously for comparison based on this definition. A subset of participants underwent transperineal ultrasound. We enrolled 173 women with mean age of 25 ± 6 years and a body mass index of 20 ± 7 kg/m2. Of the women, 67% identified as white/Caucasian, 27% black/African American, or 6% Hispanic/Latina. The mean delivery age was 39 ± 3 weeks, with 59% of participants experiencing uncomplicated VD. The MMP-9 median activity (ng/mg protein) was 242.0 (IQR, 18.7, 896.8; n = 157) in the first trimester, 130.8 (IQR, 14.6, 883.8; n = 148) in the third trimester, and 463.5 (IQR, 92.2, 900.0; n = 94) postpartum. The MMP-9 activity increased between the third trimester and 1 year postpartum (P = .006), with no significant difference between MMP-9 values in the first and third trimesters (P = .674). The vaginal angle became less acute from the first to the third trimester, and this change persisted postpartum. The vaginal angulation over the levator plate became more acute between the third trimester and postpartum in women who experienced uncomplicated VD compared to those who did not (−6.4 ± 22.1 degrees vs 17.5 ± 14.8 degrees; P = .017). Higher MMP-9 activity postpartum was associated with uncomplicated VD, with 67% of women in the third tertile achieving uncomplicated VD versus 39% in the first tertile (P = .029). Loss of vaginal angulation occurs between trimesters, and women do not recover their baseline res