Objective: To investigate whether pregnancy affects levator hiatus dimensions and the position and mobility of the bladder neck and the levator ani muscle in nulliparous pregnant women.
Methods: In the present study, 274 nulliparous pregnant women were examined at 21 weeks and 37 weeks of gestation using three-dimensional and four-dimensional transperineal ultrasonography at rest, during contraction, and during Valsalva maneuver. Levator hiatus dimensions were the anteroposterior diameter, the transverse diameter, and the area measured in rendered images. Positions of the bladder neck and levator plate were analyzed in the midsagittal plane, and mobility was calculated as displacement of the bladder neck or levator plate from rest to contraction or from rest to Valsalva.
Results: A significant increase for all levator hiatus dimension measurements was found from 21 weeks to 37 weeks of gestation. The most marked change was found for levator hiatus area at rest and during Valsalva maneuver, in which the mean area was increased by 17.1% (11.7-13.7 cm(2)) and 21.4% (15.4-18.7 cm(2)), respectively. Bladder neck mobility changed significantly during pregnancy. The most marked change was seen from rest to contraction (mean -14 mm, standard deviation 0.4).
Conclusions: An increase of all hiatal dimensions as well as bladder neck mobility was found from 21 weeks to 37 weeks of gestation in nulliparous pregnant women. The findings indicate that the changes in pelvic organ support are not solely caused by delivery, but also by physiologic changes during pregnancy.
Level of evidence: II.