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Pelvic organ prolapse (POP) is a common problem. Approximately 50% of women undergoing routine gynaecological examinations demonstrate some evidence of POP.[1, 2] It is estimated that women have an 11.1% risk of undergoing at least one operation for either POP or urinary incontinence by the age of 80.[3, 4] Pelvic organ prolapse has significant negative effects on women's quality of life and the economic consequences are anticipated to escalate with the projected increase in POP to more than 4.9 million women in the USA alone, by 2050.
Parity is a well-established risk factor for the development of POP.[6-11] The current body of evidence suggests that alterations in pelvic organ support during pregnancy and the puerperium may increase a woman's risk for POP up to eight-fold after one vaginal delivery and 20-fold following three vaginal deliveries, compared with women having the same number of caesarean deliveries.[10, 12, 13] During pregnancy, hormonal changes that prepare the pelvic floor for delivery and the increased pressure from the gravid uterus may be involved in pelvic floor relaxation. Thereafter, the passage of the baby through the birth canal is thought to result in a mechanical distortion that damages the pelvic floor connective tissue and muscular supportive structures, as well as the nerves and vessels that supply these structures.[14-17] Ultimately, these changes may lead to persistent or permanent modifications in the proper function of pelvic floor muscles. To date, our understanding of short-term and long-term structural changes in the pelvic floor that are acquired as a consequence of pregnancy and the puerperium have not been well characterised.
The introduction of the pelvic organ prolapse quantification (POPQ) system has allowed researchers to detect minimal descents in the different compartments of the pelvic floor. The purpose of this study was to evaluate objective changes in pelvic organ support in women undergoing unlaboured caesarean section (UCD) or trial of labour (TOL) from pregnancy to 1-year postpartum in a population of nulliparous women.
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This was an Institutional Review Board approved, prospective, observational study conducted in an obstetrics clinic in Wenzhou Third People's Hospital, in Wenzhou, Zhejiang, China. A total of 110 nulliparous women who were at 36–38 weeks of gestation and were planning to undergo an elective caesarean delivery or a TOL between 1 April 2009 and 31 May 2009 were recruited for participation during their routine prenatal care visit. All women with a normal, uncomplicated singleton gestation who presented to the clinical practice of the study investigator YC were invited to participate. Women were excluded if they had preterm labour, vaginal bleeding, multiple gestations, prior pelvic surgery, a known collagen vascular disorder, a pregnancy complication that precluded vaginal examination, such as placenta praevia, or if they declined participation. As UCD is much less common than TOL, recruitment was continued in both groups until the requisite 25 women were enrolled in UCD to avoid any bias in the study populations. Written informed consent was obtained from each woman who participated in the study before enrolment.
Pelvic organ support was assessed in all enrolled women, at 36–38 weeks of gestation, before the onset of labour, as well as at 6 weeks, 6 months and 1 year postpartum using the POPQ system. The examination was performed with the women in the lithotomy position. Each distance was measured using a wooden spatula marked at 1 cm intervals, and recorded in 0.5 cm increments. We obtained the individual POPQ point measurements corresponding to the anterior (Aa, Ba), apical (C, D) and posterior compartments (Ap, Bp) as well as the genital hiatus and perineal body during maximal Valsalva effort. While maximal descent may not be elicited in the lithotomy position, we wanted to ensure that consistency was maintained for all evaluations over time. Therefore, before initiating the study, the decision was made to perform POPQ in the lithotomy position to avoid any unnecessary interventions that may pose actual or perceived increased risk to the women in the advanced stages of pregnancy. If the woman was unwilling, embarrassed or judged to not perform adequate Valsalva, the measurements were taken with the woman coughing forcefully after being coached by the examiner. Total vaginal length was measured at rest. POP was defined as at least stage II descent and was determined on the basis of the most prolapsed compartment using standard criteria. To ensure consistency of testing, all women were examined and evaluated by the same experienced gynaecologist (YC), who was not involved in the labour, delivery or immediate postpartum management of any of the participants.
Demographic information including age, educational level, gravidity, smoking and breastfeeding status was collected 6 weeks postpartum. The height and weight were recorded at each evaluation as well as during the first trimester. Body mass index (BMI) was calculated as weight in kilograms/height in metres squared (kg/m2). Postpartum information about the mode of delivery and the newborn birth weight (NBW) was obtained from the clinical charts.
Participants were stratified into two groups. The UCD group included women who were scheduled for and underwent a caesarean delivery before the onset of labour. The TOL group comprised women who underwent a trial of labour. Labour was defined as regular, painful uterine contractions resulting in progressive cervical effacement and dilatation. Previous reports have documented that the prevalence of stage II POPQ at 6 weeks postpartum is approximately 45%, with a notable decrease to approximately 8% in women who undergo caesarean delivery.[20, 21] The primary endpoint of this study was POP stage at 6 weeks postpartum in UCD compared with TOL. Based on these prevalence data from other studies, it was determined that 25 women would be needed per group to detect a 37% difference in POPQ stage distribution between the two groups with 90% power to reject the null hypothesis, assuming a type I error of 0.05, or with 75% power if using a type I error of 0.01.
Descriptive data are reported as means ± standard deviation or frequency (percentages). Baseline characteristics were compared between groups using chi-square test or Fisher's exact test for categorical variables and Student's t test for continuous variables as appropriate. A mixed model repeated measurements analysis was performed to compare the postpartum trend for POPQ point measurements with covariate adjustment for measurements at 36–38 weeks of gestation. To account for the correlation between repeated measurements, a compound symmetry covariance structure was used based on the similar observed standard deviations over time. Fixed effects included group, time, age, first-trimester and 36–38-week BMI, education, NBW, gravidity, smoking status and breastfeeding as well as quadratic time and group by time interaction. Post hoc group comparison at three time-points was performed when group-by-time interaction was significant. A conservative P ≤ 0.01 was used as the significance cut-off value for adjustment of multiple comparisons. The method of generalised estimating equations was used to model the binary POP outcome that was correlated within repeated observations. The covariate adjustment was the same as that for the mixed model method. Significance was set at 5% (P ≤ 0.05), unless otherwise specified. Statistical analysis was performed with SAS 9.2 (SAS Institute, Cary, NC, USA).
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Two women achieved active labour before undergoing a caesarean delivery and were ineligible for the study. The remaining 108 women completed the study without loss to follow up. Data from 108 women were analysed, including 29 women who underwent UCD and 79 women who underwent TOL. In the TOL group, 65 women delivered vaginally (63 spontaneous and two forceps) and the remaining 14 women delivered by caesarean section. Table 1 shows the characteristics for the women in each group. The UCD group was on average, 1 year older than the TOL group (P = 0.05) and had a significantly greater BMI in the first trimester and at 36–38 weeks of gestation. At 36–38 weeks of gestation, the UCD and TOL groups had comparable POPQ point measurements with the exception of less posterior vaginal wall descent (points Ap and Bp) in the TOL group (UCD versus TOL: −2.6 ± 0.3 versus −2.7 ± 0.4, P = 0.02).
Table 1. Baseline characteristics: data are presented as n (%) for categorical variables and mean (SD) for continuous variables
|Variables||UCD (n = 29)||TOL (n = 79)||P-values|
| Age ||27.4 (2.9)||26.3 (2.4)||0.05|
| BMI at first trimester ||20.7 (2)||19.4 (1.7)||0.0005|
| Gravidity ||0.18|
|1||16 (59.3)||53 (67.1)|| |
|2||4 (14.8)||17 (21.5)|
|>2||7 (25.9)||9 (11.4)|
| Smoking status ||0.71|
|No||27 (93.1)||75 (94.9)|| |
|Yes||2 (6.9)||4 (5.1)|
| Education ||0.98|
|Primary, Grade 6||4 (13.8)||10 (12.7)|| |
|Secondary, Grades 9–12||13 (44.8)||35 (44.3)|
|College||12 (41.4)||34 (43.0)|
| Breastfeeding status ||0.23|
|No||10 (35.7)||19 (24.1)|| |
|Yes||18 (64.3)||60 (76.0)|
| NBW (g) ||3474.1 (408.1)||3335.4 (417.3)||0.13|
| POP at 36–38 weeks of gestation ||0.83|
|Yes||10 (34.5)||29 (36.7)|| |
|No ||19 (65.5)||50 (63.3)|
| POPQ components at 36–38 weeks of gestation a |
|Aa/Ba ||1.7 (0.7)||1.7 (0.6)||0.69|
|Ap/Bp||2.6 (0.3)||2.7 (0.4)||0.02|
|Perineal body ||2.5 (0.7)||2.4 (0.5)||0.87|
|Genital hiatus ||3.1 (0.6)||2.9 (0.6)||0.09|
|C||3.3 (1.1)||3.3 (0.8)||0.98|
|D||6.8 (0.6)||6.8 (0.8)||0.81|
|Total vaginal length||8.0 (0.7)||7.7 (0.8)||0.08|
Table 2 summarises the estimations of effects in multivariate repeated measurements analysis for each of the POPQ point measurements. Baseline effect at 36–38 weeks of gestation was significant for all of the measurements. More pelvic floor descent at 36–38 weeks of gestation resulted in greater overall postpartum pelvic floor relaxation.
Table 2. Repeated measurement analysis comparing the postpartum change of POPQ component measurement: data are presented as coefficient (SE) for upper panel, and P-value for lower panel
|Effects/outcomes||Aa or Ba||Ap or Bp||PB||GH|| C||TVL|
| Baseline at 36–38 weeks of gestation || || || || || || |
| Time || || || || || || |
| Time*Time || ||–||–||–|| || |
| UCD (ref = TOL) || || || || || || |
| UCD*Time ||–|| ||–||–|| ||–|
| UCD*Time*Time ||–||–||–||–|| ||–|
| Age, years || || || || || || |
| BMI at first trimester || || || || || || |
| Education ||0.49||0.14||0.01||0.79||0.01||0.64|
|Primary, grades 1–6 || || || || || || |
|Secondary, grade 7–12 || || || || || || |
| NBW (kg) || || || || || || |
| Smoking || || || || || || |
| Gravidity || || || || || || |
For points Aa and Ba, the values reflected less descent at each subsequent time-point. The rate of reduction of pelvic floor relaxation increased more dramatically at 6 weeks postpartum but gradually slowed down with time, as indicated by the quadratic effect. There was also a significant group effect; however, the group-by-time interaction did not reach significance. Specifically, the UCD group had less descent than TOL postpartum with a consistent difference noted at all time-points (effect and SE: 0.59 ± 0.09, P < 0.0001). Higher baseline BMI correlated with more anterior wall descent whereas higher NBW correlated with less descent.
For points Ap and Bp, the group-by-time interaction revealed that the magnitude of the difference between UCD and TOL increased significantly over time (effect and SE: 0.09 ± 0.05 at 6 weeks, 0.12 ± 0.05 at 6 months, 0.15 ± 0.05 at 1 year postpartum, P-values 0.05, 0.01 and 0.003, respectively). Adjusting for multiple comparisons, the UCD group had significantly less posterior wall descent than the TOL group at 6 months and 1 year postpartum.
For point C, the time effect, group-by-time interaction and the group-by-quadratic time effects were significant (P < 0.0001, 0.001 and 0.003, respectively). The UCD group had less descent than the TOL group at all three time-points postpartum and the magnitude of the difference increased over time (differences of 0.27 ± 0.10 at 6 weeks, 0.61 ± 0.10 at 6 months and 0.58 ± 0.10 at 1 year postpartum (P = 0.01, <0.0001 and <0.0001, respectively). The rate of ascent of point C increased more dramatically at 6 weeks postpartum and gradually slowed down with increased time.
For total vaginal length, the time effect was very small but it was significant. The UCD group had consistently shorter total vaginal length compared with the TOL group (difference: 0.31 ± 0.11, P = 0.01). Neither group nor time effects were significant for points perineal body or genital hiatus. Figure 1 presents the postpartum changes for POPQ measurements from both modelling prediction (closed symbols and lines) and observed data (open symbols).
Figure 1. Postpartum changes for POPQ measurements from both modelling prediction (close symbols and lines) and observed data (open symbols). In the graphs of Aa/Ba, Ap/Bp and C, the y-axis shows the absolute values relative to the hymen (cm). The true values of these points are negative numbers. In the graphs of perineal body (PB), genital hiatus (GH) and total vaginal length (TVL), the y-axis shows the true measurement value (cm). The x-axis shows the three time-points postpartum: 6 weeks (PP6w), 6 months (PP6m) and 1 year (PP1y) postpartum.
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The effects of time, quadratic time and group were all significant in the generalised estimating equations analysis (Table 3). The interaction of group by time did not reach significance (P = 0.32) and was excluded in the final model. The odds ratio (OR) was consistent over time during the first year postpartum after adjustment for POP status at 36–38 weeks of gestation, baseline BMI, age, education, NBW and smoking status (adjusted OR 0.04, 95% confidence interval [95% CI] 0.01–0.18, P < 0.0001), indicating a 96% lower likelihood of POP in the UCD group compared with the TOL group. POP at 36–38 weeks of gestation was a significant predictor of POP postpartum (adjusted OR 8.2, 95% CI 3.07–21.9, P < 0.0001). Moreover, a greater baseline BMI was associated with a higher likelihood of POP whereas a greater NBW and smoking appeared to be protective. The change in the likelihood of POP for UCD and TOL over the three postpartum time-points is shown in Figure 2. The odds of POP decreased over time in both groups but the decreased odds of POP for the UCD group compared with the TOL group remained unchanged.
Table 3. Generalised estimating equations approach predicting the risk to POP in UCD and TOL
|Effect||ORa||95% CI||P value|
| POP at 36–38 weeks of gestation ||8.19||3.07||21.9||<0.0001|
| Time ||0.92||0.88||0.96||0.0001|
| Time*Time ||1.00||1.00||1.00||0.003|
| UCD ||0.04||0.01||0.18||<0.0001|
| TOL ||1.00||–||–|| |
| Baseline BMI ||1.31||1.01||1.70||0.04|
| Age ||1.10||0.91||1.33||0.34|
| Education || || || ||0.99|
| NBW ||0.31||0.11||0.93||0.04|
| Smoking ||0.36||0.16||0.84||0.02|
| Gravidity ||1.21||0.67||2.18||0.52|
Figure 2. Postpartum changes for risk of POP in UCD and TOL from generalised estimating equations for predicted data (close symbols and lines) and observed data (open symbols). The y-axis shows odds of POP and x-axis shows the three time-points postpartum: 6 weeks (PP6w), 6 months (PP6m) and 1 year (PP1y) postpartum.
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To determine if caesarean section after TOL had a similar benefit as UCD, generalised estimating equations analysis was performed comparing the UCD group with the subset of TOL who underwent a caesarean section (Table 4). The group effect remained significant, showing that UCD was significantly more protective against POP than caesarean section after TOL (UCD versus TOL, OR 0.01, 95% CI 0.00–0.13, P = 0.0002, Figure 3).
Table 4. Generalised estimating equations approach predicting the risk to POP in UCD and subgroup of TOL who went to caesarean section
|Effect||ORa||95% CI||P value|
|POP at 36–38 weeks of gestation||2.48||2.00||69.86||0.006|
Figure 3. Postpartum changes for risk to POP in UCD and subgroup of TOL who went to caesarean section from generalised estimating equations for predicted data (close symbols and lines) and observed data (open symbols). The y-axis shows odds of POP and x-axis shows the three time-points postpartum: 6 weeks (PP6w), 6 months (PP6m) and 1 year (PP1y) postpartum.
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