Objective
We sought to study impact of delivery mode on vaginal resting pressure (VRP) and on pelvic floor muscle (PFM) strength and endurance, and whether these measurements differed in women with and without urinary incontinence.
Study Design
We conducted a cohort study following 277 nulliparous women from midpregnancy to 6 weeks postpartum. Manometer was used for PFM measurements; differences were analyzed by t test (within groups) and analysis of variance (between groups).
Results
Only VRP changed significantly (10% reduction, P = .001) after emergency cesarean section. After normal and instrumental vaginal delivery, VRP was reduced by 29% and 30%; PFM strength by 54% and 66%; and endurance by 53% and 65%, respectively. Significant differences for all PFM measures ( P < .001) were found when comparing cesarean vs normal and instrumental vaginal delivery, respectively. Urinary continent women at both time points had significantly higher PFM strength and endurance than incontinent counterparts ( P < .05).
Conclusion
Pronounced reductions in VRP and in PFM strength and endurance were found after vaginal delivery. Continent women were stronger than incontinent counterparts.
The pelvic floor muscles (PFM) play a significant role in the continence control system and pelvic organ support. The most established risk factor for pelvic floor dysfunction and weakening of the PFM is vaginal delivery. During vaginal childbirth, PFM, nerves, and connective tissue are forcibly stretched, compressed, and bruised. Neurophysiologic studies have shown that vaginal deliveries cause partial denervation of the pelvic floor striated muscles in most women, whereas imaging studies have shown major defect of the most medial part of the PFM, the pubococcygeus muscle, within the range 13–36% among primiparous women delivering vaginally. Hence, it is likely that the impact of vaginal childbirth may lead to reduced vaginal resting pressure (VRP) and reduced PFM strength and endurance, and that cesarean section (CS) may protect the PFM.
To date there is a paucity of knowledge regarding the change in VRP and in PFM strength and endurance from pregnancy to postpartum. Studies assessing change in PFM strength from pregnancy to shortly after childbirth (3 days to 12 weeks postpartum) in relation to mode of delivery have used either digital palpation, manometry, or electromyography. Except for the studies of Caroci et al and Meyer et al counting 226 and 149 nulliparous women, respectively, the sample sizes of the above-cited studies were small, ranging from 20–75 participants. This leaves very few women in each group of delivery mode. Results from above-cited studies are conflicting and none of the published studies addressed change in VRP when comparing modes of delivery. The cohort study by Elenskaia et al, including 182 nulliparous women during the second trimester, was not included as a comparable study as they discriminate between delivery modes only at their last study visit, taking place 12 months postpartum.
Pregnancy and childbirth are considered main etiological factors in the development of urinary incontinence (UI). UI in nulliparous women before and after delivery has been associated with reduced PFM strength and endurance. However, only 2 of these studies had a prospective design, following up 20 and 149 nulliparous women from pregnancy to after childbirth, respectively.
The aims of the present study were to: (1) study impact of childbirth and mode of delivery on PFM function in terms of ability to contract, VRP, and PFM strength and endurance from midpregnancy to 6 weeks postpartum; and (2) investigate changes in VRP and in PFM strength and endurance from midpregnancy to 6 weeks postpartum in women with and without UI.
Materials and Methods
This is a prospective cohort study following 300 nulliparous pregnant women from midpregnancy to 6 weeks postpartum. All nulliparous women scheduled for delivery at Akershus University Hospital, Norway from January 2010 through April 2011 were invited to participate, and they were recruited in connection with the routine ultrasound examination in gestational week 18–22 (midpregnancy).
Nulliparous women with a singleton pregnancy who could speak and understand Scandinavian languages were included. Women with a prior abortion after gestational week 16 were excluded. To attend the study visit at 6 weeks postpartum, the women had to give birth after gestational week 32. Women with stillbirth were excluded. The time point 6 weeks postpartum was chosen on the basis of convenience for the participating women, as it could be combined with their routine postpartum appointment.
Demographic data were collected through an electronic questionnaire in conjunction with participants’ first clinical visit, which was taking place shortly after routine ultrasound examination at gestational week 18–22. Data on delivery mode and other obstetric variables were collected from the hospital’s electronic medical records.
PFM measurements
During the first visit, participants were taught how to perform a correct PFM contraction. PFM contraction without any movement of the pelvis or visible contraction of the gluteal, hip, or abdominal muscles was emphasized as described in Bø et al. All examinations were performed with the participant in a standardized supine crook lying position. Correct contraction was assessed on the basis of palpation and observation and defined as inward movement and squeeze around the pelvic floor openings. VRP and strength and endurance of the PFM were measured by using an air-filled vaginal balloon connected to a high-precision pressure transducer (Camtech AS, Sandvika, Norway). The middle of the balloon was positioned 3.5 cm inside the introitus. PFM strength was calculated as the mean of 3 maximal voluntary contractions. The method has been found to be reliable and valid if used with simultaneous observation of inward movement of the perineum/catheter during the contraction. VRP was measured with the balloon positioned in the vagina without any voluntary PFM activity. PFM endurance was defined as a sustained maximal contraction, and was quantified during the first 10 seconds as the area below the measurement curve (integral calculation). The balloon was set to 0 cm H 2 O for each subject before it was placed into the vagina. Changes (Δ) in VRP and in PFM strength and endurance from midpregnancy (visit 1) to 6 weeks postpartum (visit 2) were recorded as ΔVRP, ΔPMF strength, and ΔPFM endurance. The 2 assessors were blinded for delivery data at the second visit. To minimize biases in assessment and manometer measurement, the assessors (both physiotherapists) were trained ahead of the study and a rigorous protocol in standards of procedures was kept.
UI
International Consultation on Incontinence Questionnaire (ICIQ) UI Short Form (SF) was included in the electronic questionnaire. ICIQ UI SF has been shown to have good construct validity, acceptable convergent validity, and good reliability. Women were defined as continent when answering “never” to the question: “How often do you leak urine?” (ICIQ UI SF).
Statistical analysis
Statistical analysis was performed using software (version 15; SPSS, Inc, Chicago, IL). Background and descriptive variables are presented as frequencies with percentages or means with SD. Changes from midpregnancy to 6 weeks postpartum within group regarding VRP and PFM strength and endurance were analyzed using Paired-sample t test for normally distributed data and Wilcoxon signed rank test for nonnormally distributed data. Differences between delivery modes and differences between incontinent and continent women were analyzed by using 1-way between-groups analysis of variance if data qualified for a normal distribution. If not Kruskal-Wallis test was used. Standard multiple linear regression was used to analyze the role of demographic and obstetric variables on the change of PFM measurements. P values < .05 were considered significant.
This study is part of a prospective cohort. The sample size of 300 was a result of power calculation on change in hiatal dimensions of the levator ani muscle from pregnancy to postpartum (using 3-/4-dimensional ultrasound), and not VRP and PFM strength and endurance.
Institutional review board
The study was approved by the Regional Medical Ethics Committee (2009/170) and Norwegian Social Science Data Services (2799026), and registered at ClinicalTrials.gov ( NCT01045135 ). All subjects gave written informed consent before entering the study.
Results
Three hundred nulliparous pregnant women were included at midpregnancy and 277 were seen again as primiparous at 6 weeks postpartum. Of the 23 (7.7%) women not attending the clinical examination postpartum, 10 delivered at another hospital, 9 did not want to continue, 3 had a stillbirth, and 1 was excluded due to delivery <32 weeks of gestation. Characteristics of the study sample attending both clinical visits (n = 277) are shown in Table 1 . Mean gestational week at the first study visit was 21 (SD 1.4), ranging from gestational week 17–25. After delivery, the mean postpartum week was 6.2 (SD 1.0), ranging from 3–11 weeks postpartum.
| Characteristic | Value |
|---|---|
| Age, y | 28.7 (4.3) |
| Prepregnancy BMI, kg/m 2 | 23.8 (3.9) |
| Education level | |
| College or university | 209 (75.5%) |
| Primary school, high school, or other | 68 (24.5%) |
| Marital status | |
| Married or cohabitant | 265 (95.7%) |
| Single | 12 (4.3%) |
| Smoking prepregnancy | |
| No | 207 (74.7%) |
| Yes | 70 (25.3%) |
Eleven (3.9%) of 277 women did not contract the PFM correctly at midpregnancy. At the visit 6 weeks postpartum 4 of those 11 had learned to contract correctly; 3 had a normal vaginal delivery (NVD) and 1 had CS. Seven of those 11 were still unable to perform a correct contraction; 6 had NVD and 1 had CS. Further, 5 women contracting the PFM correctly at midpregnancy had lost the ability to contract after delivery; 2 had a NVD and 3 had an instrumental vaginal delivery (IVD). This leaves 12 of 277 women (4.3%) not contracting correctly 6 weeks postpartum.
Of the 277 women 69.7% had NVD, 16.2% had IVD (41 with vacuum, 4 with forceps), and 14.1% delivered by CS (29 emergency, 10 elective). The women having elective CS were excluded from further analysis ( Tables 2-5 ). Five of the 29 women having emergency CS were in second stage of labor before CS was performed. Indication was fetal distress in 1 case and protracted total second stage in the remaining 4 cases.
| Variable PFM measures | CS (n = 29) | NVD (n = 193) | IVD (n = 45) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Gestational wk 21, mean (SD) | 6 wk postpartum, mean (SD) | Mean difference (95% CI) | P value | Gestational wk 21, mean (SD) | 6 wk postpartum, mean (SD) | Mean difference (95% CI) | P value | Gestational wk 21, mean (SD) | 6 wk postpartum, mean (SD) | Mean difference (95% CI) | P value | |
| VRP, cmH 2 O | 43.8 (12.6) | 39.5 (12.1) | 4.3 (1.6–7.0) | .003 | 42.2 (9.2) | 30.1 (6.8) | 12.2 (11.0–13.3) | < .001 | 44.8 (8.7) | 31.1 (9.6) | 13.6 (11.4–15.9) | < .001 |
| PFM strength, cmH 2 O | 35.3 (18.3) | 30.9 (16.0) | 4.4 (−0.5 to 9.4) | .077 | 35.3 (18.7) | 16.4 (12.3) | 18.9 (17.0–20.8) | < .001 | 34.8 (16.8) | 11.8 (8.3) | 22.9 (18.9–27.0) | < .001 |
| PFM endurance, cmH 2 Osec | 250.9 (134.2) | 222.3 (140.0) | 28.6 (−19.7 to 76.9) | .236 | 243.8 (137.5) | 114.7 (85.7) | 129.1 (113.7–144.4) | < .001 | 243.3 (126.1) | 86.0 (68.4) | 157.3 (126.9–187.7) | < .001 |
| Variable PFM measurements | CS (n = 29) vs NVD (n = 193) | CS (n = 29) vs IVD (n = 45) | NVD (n = 193) vs IVD (n = 45) | |||
|---|---|---|---|---|---|---|
| Mean difference (95% CI) | P value | Mean difference (95% CI) | P value | Mean difference (95% CI) | P value | |
| VRP gestational wk 21, cmH 2 O | 1.6 (−2.9 to 6.0) | .689 | −1.0 (−6.3 to 4.4) | .906 | −2.5 (−6.2 to 1.2) | .247 |
| VRP 6 wk postpartum, cmH 2 O | 9.4 (5.7–13.2) | < .001 | 8.4 (3.9–12.9) | < .001 | −1.0 (−4.2 to 2.1) | .718 |
| ΔVRP, cmH 2 O | −7.9 (−11.7 to −4.1) | < .001 | −9.4 (−13.9 to −4.8) | < .001 | −1.5 (−4.6 to 1.7) | .505 |
| PFM strength gestational wk 21, cmH 2 O | 0.0 (−8.6 to 8.6) | 1.000 | 0.6 (−9.7 to 10.9) | .991 | 0.5 (−6.6 to 7.7) | .982 |
| PFM strength 6 wk postpartum, cmH 2 O | 14.5 (8.7–20.2) | < .001 | 19.1 (12.2–25.9) | < .001 | 4.6 (−0.2 to 9.4) | .061 |
| ΔPFM strength, cmH 2 O | −14.5 (−20.7 to −8.2) | < .001 | −18.5 (−26.0 to −11.0) | < .001 | −4.0 (−9.2 to 1.2) | .160 |
| PFM endurance gestational wk 21, cmH 2 Osec | 7.2 (−56.3 to 70.7) | .962 | 7.6 (−68.4 to 83.6) | .970 | 0.4 (−52.4 to 53.2) | 1.000 |
| PFM endurance 6 wk postpartum, cmH 2 Osec | 107.7 (65.2–150.2) | < .001 | 136.3 (85.5–187.2) | < .001 | 28.6 (−6.7 to 64.0) | .138 |
| ΔPFM endurance, cmH 2 Osec | −100.5 (−151.8 to −49.2) | < .001 | −128.7 (−190.0 to −67.4) | < .001 | −28.2 (−70.8 to 14.4) | .265 |
| Variable | Factor | |||||
|---|---|---|---|---|---|---|
| ΔVRP, cmH 2 O | ΔPFM strength, cmH 2 O | ΔPFM endurance, cmH 2 Osec | ||||
| B coefficient (95% CI) | P value | B coefficient (95% CI) | P value | B coefficient (95% CI) | P value | |
| CS a | −8.0 (−11.3 to −4.6) | < .001 | −16.1 (−21.6 to −10.6) | < .001 | −111.5 (−156.6 to −66.5) | < .001 |
| IVD a | 1.2 (−1.6 to 4.1) | .403 | 1.4 (−3.3 to 6.1) | .546 | 9.6 (−29.1 to 48.2) | .626 |
| Age | 0.1 (−0.1 to 0.4) | .270 | 0.229 (−0.2 to 0.6) | .251 | 1.5 (−1.7 to 4.7) | .366 |
| Prepregnancy BMI | −0.5 (−0.7 to −0.2) | .001 | −0.4 (−0.8 to 0.1) | .101 | −3.6 (−7.2 to −0.2) | .049 |
| Length of total second stage >60 min | 1.7 (−0.4 to 3.9) | .117 | 6.9 (3.3–10.5) | < .001 | 52.5 (23.0–82.0) | .001 |
| Epidural | −0.2 (−2.3 to 2.00) | .886 | −0.8 (−4.3 to 2.8) | .668 | −12.0 (−41.3 to 17.3) | .422 |
| Fetal birthweight | 0.0 (0.0–0.0) | .546 | 0.0 (0.0–0.0) | .694 | 0.0 (−0.1 to 0.0) | .478 |
| Head circumference | −0.8 (−1.6 to 0.0) | .062 | 0.6 (−0.8 to 2.0) | .399 | 6.7 (−4.6 to 18.1) | .244 |
| PFM measure | 1. No UI a at any time point (n = 122) | 2. No UI a gestational wk 21 but UI 6 wk postpartum (n = 48) | 3. UI gestational wk 21 but no UI a 6 wk postpartum (n = 36) | 4. UI at both time points (n = 58) | P value |
|---|---|---|---|---|---|
| VRP gestational wk 21, cmH 2 O | 44.0 (10.3) | 42.4 (7.9) | 42.0 (8.2) | 41.2 (10.1) | > .05 (all comparisons) |
| VRP 6 wk postpartum, cmH 2 O | 32.6 (8.7) | 29.9 (6.4) | 31.1 (8.3) | 29.8 (9.4) | > .05 (all comparisons) |
| ΔVRP, cmH 2 O | 11.4 (9.0) | 12.6 (7.2) | 10.9 (8.1) | 11.4 (8.7) | > .05 (all comparisons) |
| PFM strength gestational wk 21, cmH 2 O | 38.2 (17.0) | 36.4 (21.0) | 34.6 (19.4) | 28.8 (16.2) | .006 (1 vs 4) > .05 (all other comparisons) |
| PFM strength 6 wk postpartum, cmH 2 O | 19.3 (14.8) | 15.8 (11.5) | 20.0 (13.0) | 12.5 (9.4) | .006 (1 vs 4) .032 (3 vs 4) > .05 (all other comparisons) |
| ΔPFM strength, cmH 2 O | 18.9 (14.8) | 20.6 (14.4) | 14.6 (13.7) | 16.3 (12.8) | > .055 (all comparisons) |
| PFM endurance gestational wk 21, cmH 2 Osec | 264.5 (121.9) | 251.9 (158.6) | 245.9 (147.2) | 199.6 (123.3) | .013 (1 vs 4) > .05 (all other comparisons) |
| PFM endurance 6 wk postpartum, cmH 2 Osec | 135.0 (105.7) | 117.0 (96.3) | 138.5 (93.7) | 86.9 (73.6) | .010 (1 vs 4) > .05 (all other comparisons) |
| ΔPFM endurance, cmH 2 Osec | 129.5 (120.5) | 134.9 (113.4) | 107.4 (122.4) | 112.7 (96.8) | > .05 (all comparisons) |
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