The present study demonstrates that in parous women, the cumulative time lengths of second stage of labor of three consecutive VDs, is not associated with UI.
The role of the second stage of labor in the development of UI is controversial, with some studies suggesting that prolonged second stage of labor is associated with a rise in complaints of UI in primiparas , while others have mixed results regarding its role in the development of UI, evaluated 3–12 months after delivery [4, 13]. Notably, in a study performed by Van Kessel et al., with a longer follow-up time interval of approximately seven years since the index delivery, no correlation was found between prolonged second stage in the first delivery and UI . Another possible contributing factor to the development of UI is the “active phase" of the second stage of labor, in which the parturient is encouraged to push. Farrel et al. found postpartum UI to be associated with the “passive” phase, but not the “active” phase, in a univariate analysis , although this did not maintain significance in a multivariate analysis. On the other hand, Groutz et al. found that among primiparas, both the length of the second stage, and the “active phase" during the second stage of labor, correlated with SUI one year after delivery .
The rate of UI in parous women ranges between 25–41% [4–6], while in the current study over 50% of women reported persistent UI more than 12 months after their last delivery, and 40% of women reported SUI. In the current study we concentrated on the time length of the 'second stages' of labor in three consecutive deliveries, as a possible factor contributing to the development of UI. We found BMI is correlated to UI complaints, but according to our findings the cumulative second stage of labor, in multiparous women, does not significantly impact the development of UI. Multiple VDs can result in cumulative obstetric injury to the pelvic floor, and damaged tissue caused by each delivery might not fully recover. The mechanisms involved in the development of UI include direct muscular damage, and/or cumulative damage to the pudendal nerves. This may explain the overall higher rate of UI and SUI in the population of multiparas we studied. Nevertheless, the net time that a parturient is exposed to the possible harmful influence of the second stage of labor, probably has no direct effect on the development of UI.
Notably, despite the relatively high rate of UI in the studied cohort, none sought any medical treatment. As UI is perceived as a “quality of life” issue, it is clearly under-treated. These findings should raise the need for patients' as well as health care providers' education, and the need to address these topics in parous women.
There are several strengths to the current study. First, its focus of a well-defined population of multiparas, with a similar obstetric background - all delivered vaginally, all deliveries were led by a midwife, and all occurred at a single center. Second, we evaluated the presence and severity of UI using the validated UDI-6 questionnaire. Third, long term follow-up was assessed in the current study. Finally, the study was powered to assess our primary outcome.
Limitations of this study should be recognized. First, we did not use an objective assessment of UI nor of other pelvic floor dysfunctions, such as anal incontinence or pelvic floor prolapse. Second, station of the fetal head, and duration of active pushing, were not assessed. In addition, the effects of second stage of labor on study outcomes among women of advanced maternal age were not assessed, as the cohort was composed of relatively younger women at the time of delivery.
In conclusion, the cumulative duration of the second stages of labor, in multiparous women, has no impact on the development of UI. In addition, UI, and specifically SUI, are probably more common than assumed among multiparas, and warrant the attention of physicians and patient education. Further studied are needed to develop safe and effective interventions to prevent the development of UI, and to investigate the effect of different risk factors with even longer follow up to menopause.