Parity, Mode of Delivery, and Pelvic Floor Disorders.

Abstract


OBJECTIVE:

This study aimed to assess the associations between parity, mode of delivery, and pelvic floor disorders.

METHODS:

The prevalence of pelvic organ prolapse, stress urinary incontinence, overactive bladder, and anal incontinence was assessed in a random sample of women aged 25–84 years by using the validated Epidemiology of Prolapse and Incontinence Questionnaire. Women were categorized as nulliparous, vaginally parous, or only delivered by cesarean. Adjusted odds ratios and 95% confidence intervals (CIs) for each disorder were calculated with logistic regression, controlling for age, body mass index, and parity.

RESULTS:

In the 4,458 respondents the prevalence of each disorder was as follows: 7% prolapse, 15% stress urinary incontinence, 13% overactive bladder, 25% anal incontinence, and 37% for any one or more pelvic floor disorders. There were no significant differences in the prevalence of disorders between the cesarean delivery and nulliparous groups. The adjusted odds of each disorder increased with vaginal parity compared with cesarean delivery: prolapse = 1.82, stress urinary incontinence = 1.81, overactive bladder = 1.53, anal incontinence = 1.72, and any one or more pelvic floor disorders = 1.85 . Number-needed-to-treat analysis revealed that 7 women would have to deliver only by cesarean delivery to prevent one woman from having a pelvic floor disorder.

CONCLUSION:

The risk of pelvic floor disorders is independently associated with vaginal delivery but not with parity alone. Cesarean delivery has a protective effect, similar to nulliparity, on the development of pelvic floor disorders when compared with vaginal delivery.

Introduction

Common pelvic floor disorders include pelvic organ prolapse, stress urinary incontinence, overactive bladder, and anal incontinence. At least 11% of women will require surgery for pelvic floor disorders in their lifetimes. Many studies suggest that vaginal delivery is associated with pelvic floor disorders. Thus, the route of delivery is a potentially modifiable risk factor. As a result, the role of elective cesarean delivery in reducing the risk of pelvic floor disorders is being debated in both the medical and lay communities. These debates are limited by an incomplete understanding of the association between vaginal delivery and pelvic floor disorders. However, an increasing number of women are requesting elective cesarean delivery, despite obstetric practice guidelines developed over the past decade aimed at reducing the cesarean delivery rate. Existing epidemiologic evidence is mixed on associations between pregnancy, labor, and mode of delivery and pelvic floor disorders. Thus, in counseling and managing women appropriately, these associations must be better understood.

The Kaiser Permanente Continence Associated Risks Epidemiologic Study (KP CARES) was designed to assess the associations between parity, mode of delivery, and the presence of the most common pelvic floor disorders and to test the hypothesis that vaginal delivery is associated with an increased risk of pelvic floor disorders compared with cesarean delivery.

DISCUSSION

This study examined the contribution of parity and delivery to the development of patient-reported pelvic floor disorders across a broad age range by using a well-validated instrument with defined predictive values. These data indicate that a woman who delivers an infant vaginally has a risk of a pelvic floor disorder that is higher than a woman who delivers all infants by cesarean delivery. Based on these data, parity itself does not increase the odds of developing a pelvic floor disorder; rather, the labor process and vaginal birth does. Overall, vaginal delivery increased the odds of any pelvic floor disorder compared with cesarean delivery by 85% when controlling for age, parity, and body mass index. Although development of pelvic floor disorders may be dependent on multiple risk factors, the attributable risk calculation suggests that vaginal birth confers one third of the burden in this population.

There are conflicting reports about the influence of parity, labor, and mode of delivery on the development of pelvic floor disorders. Our results are consistent with other epidemiological and prospective studies, which demonstrate vaginal delivery is a risk for urinary incontinence. Rortveit et al found an increased odds (2.4) of moderate or severe stress incontinence with vaginal delivery compared with cesarean delivery, with no significant difference in urge incontinence. We conducted our multivariable analyses in a similar manner, and our findings differed only in that overactive bladder was 1.5 times more common in the vaginally parous group than in the cesarean group. This difference may be reflected in our definition of overactive bladder, which included urinary urgency and frequency without leakage. In subanalyses of the cesarean group, we found that labor was associated with a trend toward increased stress urinary incontinence, but labor may not be entirely responsible for this increased risk because there remains an increased odds of stress urinary incontinence when comparing vaginal delivery with labored cesarean delivery. This is in keeping with the findings of others that cesarean delivery at any stage of labor reduced postpartum urinary incontinence.

Epidemiological studies have not determined the effect of vaginal delivery on anal incontinence. Our study found a high prevalence of anal incontinence, which could be explained by a previous lack of standard definitions and patient underreporting. Alternately, the questionnaire has a positive predictive value of 61%, which could lead to an overestimation of the prevalence of anal incontinence. However, a prevalence of solid or liquid stool incontinence of 17% is consistent with the findings of others. These studies are in keeping with our data. There was no increased prevalence of anal incontinence in the cesarean group, whether labored or not. This may reflect that anal incontinence results from a mechanical disruption of the sphincter and terminal stretch of the pudendal nerve occurring at delivery and not during labor. Other reports refute the relationship between vaginal delivery and anal incontinence by citing equal rates of anal incontinence in women delivered vaginally or by cesarean. By using the Epidemiology of Prolapse and Incontinence Questionnaire, we aimed to identify women who were bothered enough by the loss of solid, liquid, or gas material to seek medical care.

Prolapse was the least prevalent pelvic floor disorder (7%) in our population. A recent study using a validated instrument supports our findings with a prevalence of prolapse of 8%. Before our work, the relationships between parity and mode of delivery on prolapse were not well studied. Some have reported an increased degree of prolapse with increasing parity and vaginal deliveries, whereas others have shown no significant increase. As with the other pelvic floor disorders, these studies are limited by the lack of standard definitions and validated instruments. In our primary analysis, the risk of developing prolapse was significantly higher in women who had a vaginal delivery than in women who were nulliparous or had undergone cesarean. Although the odds of prolapse did not meet statistical significance, in the vaginally parous versus unlabored cesarean analysis, the odds ratio was high (5.8). There was no difference in prolapse rates when comparing labored cesarean and vaginal delivery, indicating that cesarean following labor does not protect against prolapse. Interestingly, the prevalence of prolapse was significantly higher in those women who had been pregnant but never delivered an infant compared with the nulligravid women, which suggests a multifactorial component, including exposure to the hormones of pregnancy as a risk of prolapse. Future study is necessary to confirm these relationships.

The strength of this study includes the use of a carefully validated instrument to assess a broad spectrum of pelvic floor disorders in a large, ethnically diverse population distributed across a wide age range. Although this study was not designed or sufficiently powered to completely assess the association between pregnancy and labor and the development of pelvic floor disorders, the subanalysis comparing the gravid-nulliparous with the nulliparous and the labored cesarean with the unlabored cesarean groups would suggest that prolapse may be due to a combination of factors, including the hormonal exposure of pregnancy and the act of labor, whereas stress urinary incontinence, overactive bladder, and anal incontinence are more dependent on the actual delivery event. Most studies to date have been limited by the use of nonvalidated instruments and relatively small numbers of women delivered by cesarean delivery. The use of the validated questionnaire, the broad age range, and the large sample size of this study were chosen to overcome these limitations.

There are limitations to large-scale epidemiologic studies. Our response rate was lower than anticipated, despite considerable effort. Although response rates fell short of the required 5,400 women set by the power analysis, statistically significant differences were identified for the primary outcome of cesarean versus vaginal delivery, with a power ranging between 83% and 99.9% for each pelvic floor disorder. Responder bias may have altered the results if those with or those without the disorders respond differently to the questionnaire. Additionally, birth groups and demographic information were defined by self-report, thus imposing a risk of recall bias. Recent studies have demonstrated that up to 60% of women cannot remember major delivery events, even at 6 weeks postpartum. For this reason, we did not attempt to further delineate delivery events, such as episiotomy, assisted delivery, and birth weight, for the primary analysis. Finally, indications for cesarean were determined by self-report. Prospective studies are needed to validate the associations found in our study.

Current therapies for pelvic floor disorders are frequently invasive and yield incomplete restoration of function. This makes prevention of these disorders a priority. Our study demonstrates that vaginal delivery increases the odds of pelvic floor disorders. However, the majority of women delivered vaginally did not have any pelvic floor disorders, and the risks of prophylactic cesarean delivery operation must be considered. It appears reasonable to counsel nulliparous women that prophylactic cesarean delivery would reduce the risk of a pelvic floor disorder by up to 85%. However, because these conditions affect only approximately 40% of women delivered vaginally, 5–7 women would need to deliver only by cesarean delivery to prevent one individual from developing a pelvic floor disorder.

Previous research has indicated that there is an association between birth weight, duration of the second stage of labor, instrumentation, and now, route of delivery. Translating these findings into meaningful guidelines to assist both patients and health care providers in decision making will require careful consideration and additional information.