Objective: To examine the relation between obstetric factors and the prevalence of urinary incontinence three months after delivery.
Design: 2134 postal questionnaires sent between August 1989 and June 1991.
Setting: Teaching hospital in Dunedin, New Zealand.
Subjects: All women three months postpartum who were resident in the Dunedin area.
Main outcome measure: Prevalence of urinary incontinence.
Results: 1505 questionnaires were returned (70.5% response rate). At three months postpartum 34.3% of women admitted to some degree of urinary incontinence with 3.3% having daily or more frequent leakage. There was a significant reduction in the prevalence of incontinence for women having a caesarean section, in particular in primiparous women with a history of no previous incontinence (prevalence of incontinence following a vaginal delivery 24.5%, following a caesarean section 5.2% P = 0.002). There was little difference between elective caesarean sections and those carried out in the first and second stages of labour. The odds ratios for women having a caesarean section were 0.4 (95% confidence interval (CI) 0.2.-0.7) (all women and all primiparae) and 0.2 (95% CI 0.0-0.6) (primipara with no previous incontinence) in comparison with those having a normal vaginal delivery. The prevalence of incontinence was also significantly lower in women having had two caesarean sections (23.3%; P = 0.05) but similar in those women having three or more caesarean sections (38.9%) in comparison with those women who delivered vaginally (37.7%). Other significant independent odds rations were found for daily antenatal pelvic floor exercises (PFE) (0.6, 95% CI 0.4-0.9), parity > or = 5 (2.2, 95% CI 1.0-4.9) and pre-pregnancy body mass index (1.07, 95% CI 1.04-1.10).
Conclusions: Adverse risk factors for urinary incontinence at three months postpartum are vaginal delivery, obesity and multiparity (> or = 5). Caesarean section and daily antenatal PFE appear to be protective, although not completely so.