Levator hiatus area from 21 weeks' gestation to 8 years after first delivery according to vaginal parity: prospective cohort study with an 8‐year recall extension

OBJECTIVES: The first aim was to describe longitudinal changes in levator hiatus area from 21 weeks' gestation in the first pregnancy to 1 and 8 years after first delivery, according to subsequent vaginal parity in women with vaginal delivery or Cesarean section (CS) at first delivery. The second aim was to assess the effect of subsequent vaginal delivery on levator hiatus area after first vaginal delivery. METHODS: In this prospective cohort study with an 8-year recall extension, 183 initially nulliparous women underwent three- and four-dimensional transperineal ultrasound examination at 21 weeks' gestation and 1 and 8 years after first delivery. The levator hiatus area at rest, during maximum pelvic floor muscle contraction and during maximum Valsalva maneuver was assessed at each timepoint. Participants with multiple vaginal deliveries (vaginal multiparae), only one vaginal delivery (vaginal primiparae), CS for all deliveries and vaginal birth after CS were compared. The differences between study groups in levator hiatus area over time were assessed using a linear mixed model. RESULTS: Overall, vaginal multiparae showed a statistically significant non-linear increase in levator hiatus area from 21 weeks' gestation to 8 years after first delivery (P < 0.001). In contrast, participants who delivered exclusively by CS showed a decrease in levator hiatus area from 21 weeks' gestation to the 8-year follow-up. Subsequent vaginal delivery after an initial vaginal delivery did not affect the levator hiatus area during Valsalva maneuver. At the 1-year and 8-year follow-up after the first vaginal delivery, levator hiatus area at rest remained unchanged in vaginal multiparae but decreased in vaginal primiparae. At the 8-year follow-up, vaginal multiparae had a larger hiatus area during pelvic floor muscle contraction than did vaginal primiparae. CONCLUSIONS: In this study, the levator hiatus area was influenced by the mode of the first delivery and by subsequent vaginal deliveries. Overall, the levator hiatus area increased from 21 weeks' gestation to 8 years in participants with at least one vaginal delivery and decreased in those who delivered exclusively by CS. Subsequent vaginal delivery after a first did not seem to affect the levator hiatus area measured during Valsalva maneuver. © 2026 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.