Introduction <p>Physiological changes associated with pregnancy and childbirth can affect the pelvic floor, increasing the risk of postpartum stress urinary incontinence (SUI). This study aimed to assess whether ultrasonographic risk factors for SUI identified during pregnancy are also associated with SUI in the postpartum period, as evaluated by three-dimensional high-frequency endovaginal ultrasound (3D EVUS).</p> Materials and methods <p>Fifty nulliparous pregnant women were enrolled in this prospective observational study, including 25 women with stress urinary incontinence (SUI) during pregnancy and 25 women without SUI. All participants were followed after childbirth. At the third month postpartum, participants were categorized into four groups according to the presence or absence of SUI: Group I, women without SUI during either pregnancy or the postpartum period; Group II, women without SUI during pregnancy but with SUI in the postpartum period; Group III, women with SUI during pregnancy but without SUI in the postpartum period; and Group IV, women with SUI during both pregnancy and the postpartum period. Pelvic floor and urethral characteristics were assessed in all participants using three-dimensional high-frequency endovaginal ultrasound (3D EVUS).</p> Results <p>With respect to pelvic characteristics, Group IV demonstrated a significantly longer transverse diameter of the levator hiatus (LH) compared with Groups I, II, and III. Groups I and II exhibited significantly greater bladder–symphysis distance (BSD) than Groups III and IV. Rhabdosphincter width (Rw), thickness (Rt), and volume (RV) were significantly reduced in Group IV compared with Groups I, II, and III.</p> Conclusions <p>In the postpartum period, constitutional differences in pelvic morphology, along with reduced urethral rhabdosphincter measurements, appear to constitute significant risk factors for stress urinary incontinence (SUI).</p>