Ultrasound imaging of the pelvic floor: changes in anatomy during and after first pregnancy

To describe changes in the absolute values of levator hiatal dimensions and in the contractility and distensibility of the levator hiatus during pelvic floor contraction and Valsalva maneuver, using three/four-dimensional (3D/4D) transperineal ultrasound in women during and after their first pregnancy.

Two-hundred and eighty nulliparous pregnant women underwent ultrasound examination at 12 and 36 weeks' gestation and 6 months postpartum. Hiatal dimensions were measured at rest, on pelvic floor contraction and on Valsalva maneuver. The contractility and distensibility were determined by the difference between hiatal dimensions at rest and those on contraction or Valsalva, respectively. After exclusions, there were 231 datasets from women at rest, 199 for pelvic floor contraction and 230 for Valsalva maneuver. Data at 36 weeks' gestation and 6 months postpartum were compared with data at 12 weeks' gestation.

At 36 weeks' gestation, the absolute values of hiatal dimensions and the contractility and distensibility of the levator hiatus were significantly increased compared with those at 12 weeks' gestation. Women who delivered vaginally showed a persistent significant increase in hiatal dimensions on Valsalva, whereas women who delivered by prelabor or first-stage Cesarean section showed no significant changes in hiatal dimensions on Valsalva. After both vaginal and Cesarean section delivery, there was a persistent increase in the distensibility of the hiatus during Valsalva compared with in early pregnancy.

During first pregnancy, the absolute values of levator hiatal dimensions and the contractility and distensibility of the levator hiatus increase. Regardless of delivery mode, increased distensibility of the levator hiatus during Valsalva persists after childbirth. This increased pelvic floor distensibility may play a role in the development of pelvic floor dysfunction in later life.