Specific obstetrical risk factors for urinary versus anal incontinence 4 years after first delivery

25 septembre 2013

Auteurs : X. Fritel, B. Khoshnood, A. Fauconnier
Référence : Prog Urol, 2013, 11, 23, 911-916




 




Introduction


First childbirth may become complicated by urinary or anal incontinence (UI or AI). The exact pathophysiology of postnatal incontinence is not well understood. Observable lesions such as third degree perineal tears can explain AI but this occurs in only a minority of deliveries. Other occult injury to the pelvic floor, e.g., pudendal neuropathy or levator ani muscle avulsion could affect urinary or anal continence [1]. The pudendal nerve innervates striated muscles of the pelvic floor, including levator ani, urethral sphincter and anal sphincter. Risk factors for pudendal nerve damage during childbirth are birth weight>4kg and a second active stage longer than 30minutes [2]. The levator ani muscle, which is involved in the maintenance of the urinary and anal continence, can also be injured at the time of childbirth. Using MRI findings, DeLancey reported injuries of the levator ani in 20% of primiparous women and Dietz found lesions in 36% of women using sonography [3, 4]. Risk factors for the lesions of the levator ani during childbirth are advanced maternal age, forceps delivery and the duration of the second stage [5]. The two sphincteric (urinary and anal) complexes are also bound by crossed reflex like the vesico-anal reflex [6].


Previous literature has not elucidated to what extent postnatal UI and postnatal AI result from the same underlying mechanisms of injury. The analysis of risk factors associated with postnatal incontinence suggests that certain risk factors such as advanced maternal age and parity may be common to both UI and AI [7, 8]. Other risk factors may be more specifically associated with one type of incontinence. For example, UI during pregnancy has been found to be a specific risk factor for postnatal UI and instrumental vaginal childbirth for postnatal AI [9, 10].


We hypothesized that pregnancy and delivery-associated traumatic mechanisms at the origin of postnatal incontinence differ at least to some extent for UI and AI. Therefore, specific obstetrical risk factors are likely to be associated with different types of incontinence. The analysis of risk factors related to stress UI was published previously for a portion of the population [11]. To complete this objective, we performed a secondary analysis in the whole sample of primiparous to identify both risk factors that may be common to UI and AI, and those that may be specifically associated with different types of postnatal incontinence, 4years after a first delivery.


Materials and methods


Our data were initially collected for a study aimed at comparing the risk of incontinence for women delivering in two maternity units [12]. One maternity had a policy of systematic episiotomy and the other a restrictive policy for episiotomy. The study population include nulliparous women who delivered a live-born singleton at 37-41weeks in cephalic presentation in 1996. Mothers whose current mailing address was not known (and those deceased) were excluded. Data on maternal characteristics (age, height, weight), pregnancy (gestational age, epidural, second active stage duration, delivery mode, newborns' birthweight) were collected at the time of childbirth. Women were asked to provide information about pelvic floor disorders using a postal questionnaire, which was sent 4years after childbirth. In the absence of response to the first mail, a second and if necessary a third mail was sent. The questionnaire collected data about profession and education level of the mother, interventions on the pelvic floor since childbirth, new pregnancies and pelvic floor symptoms. UI was defined by a positive response (Yes) to the question "Do you have involuntary loss of urine?" and AI was defined by the answer "Yes" to "Do you have involuntary loss of flatus or stool?" The type of UI was defined using a validated questionnaire (Bristol Female Lower Urinary Tract Symptoms questionnaire), [13] severity of UI was measured with Sandvik's score, [14] and AI was assessed using Pescatori's score, [15] as detailed in a previous publication [12]. The complete questionnaire used for the study is available online. The choice of cutoff values for continuous variables (maternal age<30, BMI<25kg/m2, gestational age<40weeks, active second stage length>20minutes, newborn weight<4000g) was done a priori. We found no evidence of a difference in the risk of UI 4years after first childbirth for women delivering in the two maternity units. However, the risk of AI was slightly higher for women who delivered in the maternity with a policy of systematic episiotomy [12]. Using data from this enquiry, we first examined risk factors associated with each type of incontinence (UI or AI) using two separate logistic regression models adjusted on maternity. All significant risk factors for UI or AI were then included in a multinomial logit analysis to assess specific risk factors for the following outcomes: UI only, AI only, and UI+AI. Variables for mode of delivery, third degree perineal tear and maternity unit were forced in the model irrespective of their statistical significance in the logistic models. We used estimates of the odds ratios in the multinomial model for each risk factor and outcome in order to examine the extent to which specific risk factors may be associated with different types of incontinence.


We complied with French laws on data confidentiality, and restrictions on type of data collected (e.g. no religious or racial data). Informed consent was obtained from all study participants.


Results


Among the 1323 primiparous women who met inclusion criteria, postal address was no longer valid for 548 (41%) and one had died, 774 (59%) women received the postal questionnaire and 627 (81%) completed it. The first delivery was spontaneous vaginal in 368 cases, instrumental in 209 cases (95 by vacuum) and by cesarean section for 50 women. Continence disorders 4years after first childbirth of the 627 women who responded are summarized in Table 1. The prevalence of UI was 29% (n =181) and that of AI 13% (82), 22% of women (140) reported UI only, 6.5% (41) AI only, and 6.5% (41) both UI and AI.


Risk factors for UI (with or without AI) were maternal age≥30 at first delivery (adjusted OR, 2.3 [95% CI 1.5-3.4]), UI before first pregnancy (10.2 [3.7-28.1]), and UI during first pregnancy (3.3 [2.1-5.1]). Risk factors for AI (with or without UI) were UI before first pregnancy (adjusted OR 5.2 [95% CI 2.3-11.8]), no epidural (versus yes) during first delivery (2.4 [1.2-4.8]), second active stage>20min (2.5 [1.2-5.1]), and occurrence of third degree perineal tear during first delivery (13.3 [2.1-83.0]). Other factors tested and non-significant were: education level, a BMI greater than 25kg/m2, gestational age at first delivery, a first newborn over 4000g, pelvic floor exercises after first delivery, episiotomy at first delivery, a second delivery (this concerns 381 women), and an ongoing pregnancy (Appendix A).


Table 2 presents the results of the multinomial logistic regression analysis to assess specific risk factors associated with UI only, AI only, and UI+AI. Estimates suggested that different risk factors were associated with the three outcomes. Risk factors associated with UI only were maternal age at delivery≥30 (adjusted OR 2.3 [95% CI 1.5-3.5]), pre-existing UI (6.4 [2.2-19.0]) and UI during pregnancy (3.6 [2.2-5.9]), whereas risk factors for AI only were duration of the second active stage>20min (2.9 [1.1-7.1]), and third degree perineal tear (20.9 [1.7-252]). Risk factors significantly associated with UI+AI were maternal age>30years (2.6 [1.3-5.5]), UI before pregnancy (32.9 [9.0-120]), no epidural (4.3 [1.6-11.1]) and third degree perineal tear (20.0 [1.3-314]).


Discussion


To our knowledge, this is one of the few studies that evaluated specific risk factors associated with UI and AI 4years after first delivery. One previous study, which looked at specific risk factors for UI and AI, was based on data collected 6months after first childbirth [16]. This study found that risk factors were different for postnatal UI (shoulder dystocia and vaginal delivery) vs. postnatal AI (age over 35years, smoking, duration of the second stage of labor more than an hour and third degree perineal tear).


We found that different risk factors were associated with UI only (i.e., without AI), AI only, and UI+AI 4years after first delivery. Risk factors for UI only were maternal age at first delivery≥30, pre-existing UI and pregnancy UI. Risk factors associated with AI only were length of the second active stage>20minutes and third degree perineal tear. Risk factors associated with UI+AI were age≥30, no epidural, third degree perineal tear, and UI before pregnancy.


The relatively long period of follow-up in our study (4years after first delivery) is an important advantage as the prevalence of postpartum UI tends to decrease spontaneously in the first postpartum year [17]. Nevertheless, our study has certain limitations. The sample size of the study was based on the number of subjects needed to have sufficient power for showing a difference in the outcomes between the two maternities that had different policies for episiotomy in our initial study [12]. The study was not specifically designed to have sufficient power to explore the specific effects associated with different risk factors. Indeed, the confidence intervals for the estimates of the effects for several risk factors were wide and lack of sufficient power may explain the absence of statistically significant results for some of the risk factors in the present study. In particular, the lack of statistical significance for the associations between mode of delivery and outcomes (different types of incontinence) is likely to be due to insufficient power. It is worth noting that the point estimates (odds ratios) suggested a lower, albeit not statistically significant, risk for all three outcomes (UI only, AI only and UI+AI) for women who delivered following a cesarean section. For reasons of statistical power we also renounced conduct an analysis based on the type of instrument used for delivery (forceps or vacuum).


Our findings of specific associations between obstetric risk factors and prevalence of UI only, AI only and UI+AI may be due to differences in the underlying mechanisms of injury for different types of incontinence. The two main mechanisms proposed to explain postnatal AI are sphincter injury and pudendal neuropathy. In our study, the specific risk factors for AI (third degree perineal tear and prolonged second active stage) are compatible with these mechanisms. Prolonged active second stage is associated with pudendal nerve damage [2]. Even following repair, third degree perineal tear is associated with AI years after delivery [18].


Concerning postnatal stress UI, the mechanisms of injury are still largely unknown [17]. Vaginal birth is likely to increase the mobility of the urethra or to be accompanied by lesions of the levator ani [3, 4]. However, urethra mobility returns to prenatal values a few months after delivery [19]. Wijma et al. found no relation between urethra mobility and postnatal UI [20]. Dietz and Lanzarone found no link between levator ani avulsion and postnatal stress UI [4]. DeLancey et al. reported that only 16% of postnatal stress UI could be explained by urethra mobility, whereas urethra closing pressure could account for 25% of postnatal de novo stress UI [21]. The relation between urethra closure pressure and pregnancy remains unclear. Iosif et al. found closure pressure to increase during pregnancy and to decrease after delivery, while Le Coutour et al. reported opposite findings [22, 23]. In our study, the finding of an association between maternal age and UI could be explained by a lower urethra closure pressure as the latter is known to decrease with increasing maternal age [24]. We are not aware of any studies that have examined the link between pregnancy UI and urethra closure pressure or urethral mobility [17].


In conclusion, our results suggest that UI and AI 4years after first delivery do not share the same set of risk factors. These results are consistent with the hypothesis that the underlying mechanisms of postnatal incontinence differ for UI versus AI. This implies in turn that different strategies may be needed for prevention of UI and AI.


Disclosure of interest


The authors declare that they have no conflicts of interest concerning this article.



Appendix A. Supplementary material


(150 Ko)
  
(161 Ko)
  
(154 Ko)
  



☆  Level of evidence: 3.





Table 1 - Continence complaints 4years after first childbirth. Where percentages do not add to 100%, there were some missing data (from 0 to 3.3%).
Continence troubles 4years after first childbirth 
  n =627  n (%) 
Urinary incontinence (UI)  No  438 (71) 
  Yes  181 (29) 
 
Severity of UI (Sandvik score)  No UI  438 (71) 
  Slight  110 (18) 
  Moderate  42 (7) 
  Severe  16 (3) 
 
Type of UI (% among women with UI)  Stress  55 (30) 
  Urgency  12 (7) 
  Mixed  109 (60) 
 
UI bothersome (% among women with UI)  Not a problem  24 (13) 
  A bit of a problem  107 (59) 
  Quite a problem  27 (15) 
  A serious problem  17 (9) 
 
Anal incontinence (AI)  No  525 (84) 
  Yes  82 (13) 
 
Type of AI (% among women with AI)  Flatus only  64 (78) 
  Stool  18 (22) 
 
AI bothersome (% among women with AI)  Not a problem  1 (1) 
  A bit of a problem  36 (44) 
  Quite a problem  13 (16) 
  A serious problem  30 (37) 





Table 2 - Risk factors for urinary incontinence (UI) only, anal incontinence (AI) only, and UI+AI. Multinomial logistic regression adjusted on maternity. Other factors tested and non-significant were: education level, a BMI greater than 25kg/m2, gestational age at first delivery, a first newborn over 4000g, pelvic floor exercises after first delivery, episiotomy at first delivery, a second delivery, and an ongoing pregnancy. Case numbers may not add up because of some missing data for given risk factors (from 0 to 4.6%).
Variable  n   UI only adjusted OR (CI 95%)  AI only adjusted OR (CI 95%)  IU+IA adjusted OR (CI 95%) 
Age at first childbirth 
<30years  415  1  1 
≥30years  212  2.27 (1.47-3.49)  1.34 (0.65-2.73)  2.65 (1.29-5.46) 
 
UI before pregnancy 
No  565  1  1 
Yes  33  6.44 (2.19-19.0)  2.02 (0.21-18.9)  32.9 (9.00-120) 
 
UI during pregnancy 
No  468  1 
Yes  133  3.64 (2.25-5.91)  1.57 (0.64-3.90)  1.87 (0.77-4.55) 
 
Epidural 
No  101  0.96 (0.51-1.78)  1.52 (0.59-3.92)  4.29 (1.65-11.1) 
Yes  526  1 
 
Second active stage 
≤20minutes  561  1 
>20minutes  59  1.26 (0.62-2.57)  2.86 (1.15-7.13)  2.29 (0.73-7.15) 
 
Mode of delivery 
Spontaneous  368 
Instrumental  209  1.16 (0.74-1.81)  1.11 (0.54-2.31)  0.96 (0.43-2.11) 
Cesarean  50  0.54 (0.22-1.31)  0.61 (0.14-2.79)  0.28 (0.05-1.70) 
 
Third degree perineal tear 
No  621  1  1 
Yes  3.67 (0.22-61.3)  20.9 (1.73-252)  20.0 (1.28-314) 



Légende :
Bold characters indicate a significant association (P <0.05).


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