The prevalence of incontinence increased with age (Table 3). As many as 3,083 (15.4%) nulliparous women reported incontinence before pregnancy. However, the prevalence was significantly higher among parous women, as 4,662 (33%) primiparous women and 3,549 (40%) multiparous women reported incontinence. The prevalence also increased with increasing BMI (Table 3). Adjusted analyses showed an attenuated association between age and incontinence as compared with unadjusted analyses, whereas corresponding results for BMI and parity essentially remained the same (Table 3).
Urinary incontinence was reported by 25,121 (58.1%) women during pregnancy (Table 1). Stress urinary incontinence was the most common type, reported by 6,171 (30.9%) nulliparous and 9,790 (42.0%) parous women. Among women who were continent before pregnancy, the cumulative incidence of any incontinence was 45.6% (13,978/30,631) by week 30 of pregnancy. The cumulative incidence was 31.5% (9,634/30,631), 4.0% (1,231/30,631), and 10.2% (3,113/30,631) for stress, urge, and mixed incontinence, respectively.
Weekly leakage or more was reported by 9,373 (21.7%) in association with coughing or laughing, by 2,839 (6.5%) in association with running or jumping, and by 3,228 (7.5%) who had symptoms associated with urgency (Table 2). During pregnancy, leakage of droplets was much more common than leakage of larger amounts regardless of triggering situation, with 2,140 (4.9%), 966 (2.2%), and 919 (2.1%) leaking “larger amounts,” respectively.
The prevalence of incontinence in pregnancy increased with increasing parity, BMI, and age (Table 3). Among nulliparous women, 9,586 (48.0%) were incontinent during pregnancy; still, the prevalence was significantly higher among parous women (66.6%). Adjusted analyses resulted in only minor reduction in ORs for all variables in the model.
When comparing urinary incontinence before and during pregnancy in Table 1, the increase in prevalence is two-fold for SUI and three-fold for mixed urinary incontinence (Table 1). “Coughing, laughing, or sneezing” was the situation most strongly associated with an increase of prevalence of urinary incontinence during pregnancy. Table 2 shows that the increase in prevalence of symptoms during pregnancy was predominantly due to slight symptoms (Frequency “1–4 times a month” or “1–6 times a week” and “Droplets” for amounts).
Even though the absolute figures for urinary incontinence were much higher in pregnancy, the relative associations between incontinence and age or BMI were similar before and during pregnancy. The association between incontinence and parity, however, was weaker in pregnancy than before, and especially so for women of parity 2 or more (Table 3). However, parity still remained a strong risk factor for urinary incontinence in pregnancy.
In this large population of pregnant women, the prevalence of any incontinence was doubled compared with the prevalence before pregnancy. The increase was due to the stress incontinence component, thus increasing SUI and mixed urinary incontinence. Symptoms tended to be mild both before and during pregnancy. Parity was a strong risk factor among nonpregnant women, less so among pregnant women, whereas age and BMI were weak risk factors in this population of young women.
A major strength of this study was the size of the observational cohort. We did not come across any study this large concerning incontinence during pregnancy when searching PubMed (English language; January 1966–July 2006; limited to adolescent, adult, middle aged; search terms “urinary incontinence” and “pregnancy”). Narrow confidence intervals strengthened the precision of the results.
The Norwegian Mother and Child Cohort Study invited all pregnant women in Norway to participate, underscoring that the target population of MoBa was a population-based and nonselected sample. The response rate was 45%. The study population may not be representative of pregnant women during the investigated period in every respect. There were, however, only minor differences between the MoBa participants and their births compared with the total number of births in the same period concerning distribution of demographic variables.11 Even though the study population was representative of Norwegian pregnant women in many aspects, it is possible that there was a socioeconomic gradient that influenced prevalence estimates, because women in lower socioeconomic classes were underrepresented. The main selection was related to the rate of recruitment. Risk factors such as age, BMI, and parity may be distributed differently in low-income pregnant women. This may have introduced a bias, most probably toward a lower prevalence than in the total population. On the other hand, there is no reason to believe that there was a selection bias on the basis of incontinence status, because the MoBa was a survey covering many topics, with urinary incontinence questions only being a minor issue. We believe that effect estimates for the risk factors investigated in this study were not affected by a significant selection bias.
Our estimate of prevalence before pregnancy stems from a pregnant population, and this may introduce a bias, based on awareness, toward a higher prevalence. As mentioned, selection bias due to disease status is unlikely to occur. Additionally, large cohort studies from Australia and Norway have reported similar prevalence of urinary incontinence among a general population of women aged 18 to 50 years, with 24.2% and 25.0%, respectively.2,4 A wide range of prevalence figures has been presented among both nulliparous (5–39%) and parous (19–48%) women.13–15 It does not seem likely that there is a large recall bias resulting in higher prevalence of urinary incontinence. Prevalence of incontinence during pregnancy also varies widely in previous studies, with figures ranging from 4–53% among nulliparous women, and from 14–84% among parous women.7,8,14,16–18 Our prevalence estimate of 58.1% of incontinence during pregnancy distributed unevenly on three types of urinary incontinence was based on real-time report of symptoms in a large, unselected population, similar to figures reported in other prospective studies of pregnant women.6,19,20
Epidemiologic data are scarce on cumulative incidence of urinary incontinence during pregnancy. We reported a cumulative incidence of 45% of any incontinence, which is higher than earlier reported (12% and 16.7%).14,21 However, both studies were based on recall data, which may have influenced the estimate. The increase of incontinence in pregnancy was mostly due to increased prevalence of SUI and mixed urinary incontinence. This is in line with findings in previous studies that have investigated the effect of pregnancy on type of incontinence.18,22,23 Several studies on incontinence during pregnancy have reported data on stress incontinence only, with estimates between 9% and 85%7,16,22,24,25 The different prevalence estimates could partly be explained by use of questionnaires at different points during pregnancy, by retrospective or prospective design and by use of subjective or objective measurements. Our estimate of 32.3% was in the middle of the published range. Pregnant women were less likely to run and jump, which may explain why the prevalence of incontinence in such situations increased only moderately during pregnancy. We used a low severity threshold to include incontinent women. Our urinary incontinence definition was based on terminology from the International Continence Society.12
Although the questionnaire itself was not specifically validated, it used the answer options “Droplets” or “Larger amounts” to measure amount of leakage. In Norwegian, the common understanding of these answering alternatives would be close to the phrasing in the validated Sandvik's Severity Index.26 Few previous studies have looked into changes in severity of symptoms as a result of pregnancy. Women in our study generally reported mild symptoms, both before and during pregnancy. This finding is in line with results from other studies.6,8,19,24 This implies that incontinence in pregnancy should not be regarded as a major problem as such. However, a recent study suggests that incontinence in pregnancy may be a risk for incontinence later in life.27
Age, parity, and BMI are three main risk factors for incontinence in younger women.4,6,7,13–15,17,28 In the present study, adjusted analyses showed that parity was the strongest risk factor for urinary incontinence among both nonpregnant and pregnant women, with OR around 2 for parous women. This is in line with other studies.19,25,29 Some authors have found a certain threshold for the number of deliveries as risk factor for incontinence.15,30 Our findings support that the first delivery has the strongest effect on urinary incontinence before a new pregnancy, but subsequent deliveries also add to the risk for incontinence. However, the association with parity was less strong among pregnant women, indicating that pregnancy itself becomes a more important risk factor for incontinence when pregnant.
Studies have shown that having incontinence before pregnancy is a significant risk factor of incontinence during pregnancy.6,14 It was not surprising that women who were incontinent at the start of pregnancy did not get better in pregnancy. However, women who had been incontinent previously, but were continent at the start of pregnancy, represent an interesting group. It is not clear from previous studies if this group was at increased risk of incontinence during pregnancy. Our data did not allow us to distinguish between these two groups of women with incontinence in this situation.
In conclusion, this large study of pregnant women confirmed that incontinence in pregnancy is highly prevalent. The increase of prevalence compared with the nonpregnant state was mainly due to stress and mixed incontinence. Generally, pregnant women had mild symptoms. In pregnancy, parity was less strongly associated with incontinence compared with the prepregnancy state, probably because pregnancy becomes a strong risk factor in itself. The risk of longstanding and progressively more severe incontinence among women who were incontinent during pregnancy should be investigated in further studies.
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