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Research Studies

Pregnancy is an important risk factor for urinary incontinence one year after delivery in primiparous women compared with nulliparous women

Hansen BB, Svare J, Viktrup L, Jørgensen T, Lose G. Urinary incontinence during pregnancy and 1 year after delivery in primiparous women compared with a control group of nulliparous women. Neurourol Urodynam 2012; 31 (4): 475-480.

Why they did the study

Pregnancy and delivery are established major risk factors for urinary incontinence (UI) among primiparous and multiparous women and different obstetric factors may contribute to the risk. However, the individual contribution of each factor has been rarely investigated. Most studies reporting prevalence of UI in parous women are also cross-sectional or cohort studies without a control group. In fact, a cohort study of primiparous women, with an age-matched control group of nulliparous women, has not been previously performed. The aim of this study was to follow a group of primiparous women shortly after delivery, and an age-matched control group of nulliparous women, for 1 year to assess prevalence and types of UI in the two groups and study the independent impact of the first pregnancy and delivery on the continence status.

How they did it

This was a prospective cohort study conducted in Denmark.  All primiparous women older than 17 years who in the period from June 2003 to July 2005 delivered live born babies in the University Hospital of Copenhagen were asked to participate in the study. They were asked to fill out a questionnaire 2–3 days after the delivery, during their stay in the hospital. One year after the delivery, a new, and almost identical, questionnaire was mailed to those women who responded to the first questionnaire. The control group was randomly selected among women with no registered deliveries and who lived in the same geographic area as the women in the primiparous group. This was possible due to the Danish Civil Registration System, in which all inhabitants in Denmark are registered by a unique 10-digit number, which follows them lifelong and which is used in all contacts with the health care system. An attempt to match the two groups, with respect to age in 5 years intervals, was done.  A questionnaire was mailed to the control group at baseline and a second identical questionnaire was mailed 1 year later to those who responded.

The questionnaires were divided into 2 parts. The first part contained questions about socio-demographic characteristics, life style factors, pre-existing morbidity and conditions (including previous miscarriages or legal abortions), and use of medicine for the last 3 months. The second part contained questions about UI.  Questions about UI were based on the validated Danish version of the validated International Consultation of Incontinence Questionnaire Short Form (ICIQ-SF). Urinary incontinence was defined as any urinary leakage according to the International Continence Society.  Depending on their answers in the ‘‘When leakage’’ item, most of the incontinent women (81%) could be classified as having stress incontinence (leakage when coughing, sneezing or physically active), urge incontinence (leakage before getting to the toilet), or mixed incontinence (combination of stress- and urge-incontinence). ICIQ-SF scores, which sum up scores in the first three items in ICIQ-SF were calculated among the incontinent women. The ICIQ-SF score represents a combined severity and bother-score, with range 0–21. Logistic regression analyses were used to adjust for potential confounders when comparing the prevalence of UI between the two groups at baseline and after 1 year.

What they found

The eligible numbers of primiparous women were 1,604, and 1,018 (63%) completed and returned this first questionnaire. One year after the delivery, 799 (80%) women responded to this second questionnaire, comprising 52% of the eligible women and represented the primiparous group 1 year after delivery. A total of 1,836 women of the control group (N=3000) responded to the first questionnaire (61%). One year later, 1,382 (75%) responded on the second questionnaire, comprising 45% of the original random sample and represented the control group after 1 year.

Based on the answers in the ICIQ-SF at baseline, the prevalence of any type of incontinence was 32% in the primiparous group compared with 14% in the control group. After 1 year, the prevalence was 29% and 17%, respectively. With adjustment for potential risk factors, the prevalence of all UI during pregnancy was 3.3 times higher than the prevalence in a control group of nulliparous women. One year after delivery, the difference was reduced to 2.5 times higher in the primiparous group than in nulliparous women.

The prevalence of stress incontinence in particular differed in the two groups. At baseline stress incontinence was 3 times more frequent in the primiparous group. The difference was reduced after 1 year, but still significant. In the primiparous group, the prevalence of stress incontinence was reduced significantly (P < 0.001) from baseline to after 1 year. In the control group, there were no significant differences in the prevalences of any of the three types of incontinence between baseline and after 1 year. The rate of caesarean delivery in the primiparous group was 22.3% and the number of twin pregnancies was 36 (3.6%).
The mean ICIQ-SF scores in a combined severity- and bother-score indicated that the symptoms were mild to moderate in both groups at baseline as well as after 1 year. There was no significant difference in the mean scores between the incontinent women at baseline or after 1 year in both groups.

Why it matters

Urinary incontinence is a common condition during pregnancy and after childbirth. Although delivery was traditionally considered to be the major risk factor for UI following delivery, the net contribution of pregnancy seems equally important.  Several studies suggest that lower urinary tract symptoms including incontinence are common during pregnancy and increase with increasing gestation until term. The symptoms promptly decrease after delivery but tend to recur and worsen during subsequent pregnancies indicating that pregnancy may play a role. Although the exact mechanisms during gestation remain obscure, increased urine production, degenerative changes in the autonomic innervation of the lower urinary and urinary bladder function, mechanical pressure exerted by the gravid uterus and elevated elastolytic activity with softening of the collagenous supports of the bladder neck and proximal urethra may be responsible.

This large prospective cohort study found that the overall prevalence of UI immediately after delivery in primiparous women and in nulliparous groups were 32% and 14%, respectively and after 1 year were 29% and 17%, respectively. Since the 2 groups were almost comparable, much of the difference was a consequence of pregnancy and delivery. Urinary incontinence observed immediately after delivery is more likely a continuation of UI that has developed during pregnancy. The ICIQ-SF scores, among incontinent women at baseline and after 1 year, did not differ between the two groups. This indicated that primiparous women did not just perceive their UI as a natural consequence of pregnancy and delivery, but that their symptoms were as serious and bothersome as among nulliparous women.
An interesting finding was that adjusted prevalence of UI in the primiparous group was higher immediately after pregnancy than 1 year after delivery compared to nulliparous women. This indicates that pregnancy is equally important to delivery as a risk factor for UI. Urinary incontinence was not uncommon among nulliparous women and stress incontinence was the most frequent type of UI reported in both groups.

Primiparous women were not asked about UI during pregnancy at baseline but were interviewed 2-3 days after delivery.  Although the 2 groups were matched for age, there were other differences between that could represent a potential risk of selection bias in this study. Furthermore, the relationship between known obstetric risk variables, such as duration of labor, operative delivery and birth weight, and UI were not studied. Therefore, in further prospective cohort studies, primiparous women should be interviewed about UI during pregnancy and rigorously matched with controls. All potential risk factors for post-delivery UI should be studied.

Next question

The presence of any UI (even a small amount once a week or less often) is abnormal. When this definition is used, UI was found to be a highly prevalent condition immediately after delivery and up to 1 year with bothersome effects even in young and middle-aged primiparous women. The results of this study highlight the importance of standardizing the definition of UI and that UI reported very early after delivery probably represents development of the symptom during pregnancy. This study thus provides further epidemiological data to support that pregnancy alone has a detrimental effect on continence mechanisms independent of the delivery process particularly stress incontinence. Further clinical studies are needed to clarify the mechanism of pregnancy-induced UI and to determine the hormonal factors that could be primary responsible.

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