Hiatal Changes in Multiparous Women during Pregnancy and after Delivery: A Prospective 3D-Transperineal Ultrasound Study

Background: Few studies have examined the impact of subsequent deliveries on levator hiatus morphology and no study has described its changes throughout gestation and postpartum in multiparous women. The aim of this study was to investigate the changes that occur in the levator hiatus (i) during pregnancy, and (ii) after labor in a cohort of multiparous women. Pregnant women with a history of vaginal birth were compared to those with a history of cesarean section (CS). Methods: Prospective cohort longitudinal study, consisting of 82 multiparous women who were examined and recruited at an antenatal clinic. All participants underwent real-time three-dimensional transperineal ultrasound (3D-TPUS) evaluation of the levator ani at 12, 22, and 32 weeks of pregnancy, as well as 4–6 months after delivery. 3D volumes were acquired and stored for offline analysis. Results: Data from 66 women with at least two measurements were available for analysis. 31 had a history of vaginal delivery (VD) and no history of CS (Group 1), while 35 had a history of previous CS and no history of vaginal birth (Group 2). When comparing levator ani dimensions at rest, during Valsalva, and pelvic floor muscle contraction (PFMC) in the third-trimester to those in the first-trimester, almost all hiatal dimensions were statistically significantly enlarged. Postpartum hiatal dimensions were lower compared to third-trimester measurements in both groups. The incidence of new levator trauma in Group 1 was 3.7%. Conclusions: In multiparous women: (a) ultrasound (US) measurements of the levator hiatus increased significantly between the first-, second-, and third-trimester, and (b) many of the levator hiatus dimensions decreased significantly postpartum, regardless of whether the delivery was a non-traumatic vaginal birth or a CS. The incidence of new levator trauma is reduced in multiparous women with a history of previous vaginal births who deliver vaginally.