Abstract
Background. The cause of transient stress urinary incontinence during pregnancy remains uncertain. Anatomical change, such as a pressure effect of the enlarged uterus, changes in renal function, and alterations in bladder and urethral function have been proposed. There is little information about the role of reproductive hormones in stress urinary incontinence with onset during pregnancy. Methods. In a prospective, longitudinal, observational cohort study 200 consecutive women attending in early pregnancy were observed by repeated measurements of stress urinary incontinence, its possible determinants as well as serum concentrations of progesterone, estradiol and relaxin. Results. The prevalence rate of stress urinary incontinence increased to a stable level of about 25% from mid-pregnancy and increased with parity. A higher serum relaxin value early in pregnancy was correlated to a lower prevalence rate of stress urinary incontinence with onset during pregnancy, also when the influence of potentially important factors was taken into account in a multivariate analysis. No significant difference was shown regarding serum concentrations of estrogen or progesterone, maternal age, weight gain, time since last delivery or smoking, although this can be due to a small sample size. Conclusion. The reproductive hormone relaxin might have a role in maintaining urinary continence during pregnancy. A mechanism is uncertain.