Parity is an established risk factor for stress urinary incontinence (SUI) among young and middle-aged women (1), but the underlying etiology is not completely understood. It is well documented that postpartum SUI increases the risk of long-term persistent incontinence (2), but the mechanism involved remains unknown. The aim of this study was to investigate the constitutional, pregnancy, labour and delivery factors involved in the long-term persistence of SUI from postpartum period to 12 years after first delivery. The study hypothesis was that both pregnancy and delivery factors may play a role in the long-term persistence of SUI.

A longitudinal cohort study was undertaken to evaluate the influence of first pregnancy and delivery on the development of stress urinary incontinence. The study group was selected from the primigravid women who came to give birth at our Public Health Hospital from April to October, 2007. Our aim was to investigate only the new cases of SUI, so those women who made reference to any kind of urinary incontinence (UI) before pregnancy were excluded from the study. Other exclusion criteria were: multiple pregnancy, gestational age of less than 37 weeks, diabetes mellitus or a maternal history of the condition, previous urogynecological surgery or in the follow up period, urogynecological malformations and neurological disorders. An interview on urinary symptoms was held facetoface at inclusion and 6 months postpartum using the 2002 ICS definitions (3). Information about first labour and delivery was obtained from the clinical charts. Twelve years after first delivery two questionnaires were sent by postal mail to all the women who had attended the follow up visit at six months postpartum. The first one included questions about urinary symptoms, parity, menopausal status, weight and urogynecological surgery. Women were also request to answer the Spanish version of the International Consultation of Incontinence short form questionnaire (ICIQ-SF). Severity of incontinence was classified according the Incontinence Severity Index (ISI). Those women who did not respond to the mailed questionnaires were contact by telephone, and answered the same questions. Correlation of clinical and demographic characteristics with the persistence of SUI was examined by comparison of percentages (Chi-square and Fisher’s test). Statistical significance was set as p=0.05. A multiple logistic regression model was performed with the variables close to statistical significance (p<0.2).

During the inclusion period, 479 pregnant women at term who came to give birth at our hospital were interviewed. Twenty-one (4.4%) women complained of UI prior to pregnancy and were consequently excluded. Six months postpartum, 381 attended the follow-up visit. Of those 318 (83.5%) were contacted twelve years after first delivery and answered the questionnaires. We excluded 3 women because a SUI surgery was performed in the follow-up period. The remaining 315 women formed the study group. Mean age was 43.4 years (range: 30-55); mean BMI was 24.0 (range:15.6- 51.2) and mean parity was 1.8 (range: 1-8). Of the total, 87(27.6%) had only one delivery, 200 (63.5%) two, 23 (8,3%) three, and the remaining two (0.6%) more than three. Mode of first delivery was vaginal in 275 (83.3%) women, and cesarean in 40 (12.7%). Of those who had had a caesarean, 16 had a subsequent vaginal delivery. SUI affected 44 (14.0%) women 6 months postpartum and 125 (39.7%) 12 years after first delivery. SUI persisted from postpartum period to 12 years after first delivery in 36 women. Nine (25%) women also had symptoms of urge urinary incontinence. The ISI distribution was 19 (52.8%) slight, 15 (41.7%) moderate, and two (5.6%) severe. The mean score of the ICIQ- SF was 7.13 (SD, 3.51).
The results of the univariate analysis performed to correlate long-term persistence of SUI with different variables are shown in table 1. Women who were incontinent during pregnancy, with epidural anesthesia during labour, and those who had been pushing more than 60 minutes in the second stage of labor were more at risk of persisting with SUI. A multiple logistic regression model was performed with these variables, and those close to statistical significance (augmentation with oxytocin). Age, Body Mass Index (BMI) and parity were also included as potential confounding factors. The multivariant model indicated that both pregnancy SUI (OR: 4.54; 95% CI: 2.10–9.80) and active 2nd stage of labour ≥ 1 hour (OR: 3.68; 95% CI: 1.21–11.14) were independently associated with persisting SUI 12 years after delivery. We did not find any statistical association with the other variables.

These results suggest that some of the changes that are involved in the long-term persistence of SUI after childbirth may have its origin during pregnancy. We have also identified an independent association between active 2nd stage of labour ≥ 1 and long-term persistent SUI. These results provide new information about the mechanism by which parity is linked to SUI and give us the opportunity of prevention. First of all, performing intensive pelvic floor muscle training during pregnancy in order to prevent pregnancy SUI. Secondly, avoiding an active second stage of labour more than one hour.

Women who were incontinent during pregnancy, and those who had been pushing more than one hour in the second stage of labour were more at risk of persisting with SUI from postpartum period to long term after delivery. We were able to demonstrate this independent association taking into account different constitutional, pregnancy, labour and delivery variables.

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