Abstract
INTRODUCTION AND HYPOTHESIS: The failure of the levator hiatus (LH) and urogenital hiatus (UGH) to remain closed is not only associated with pelvic floor disorders, but also contributes to recurrence after surgical repair. Pregnancy and vaginal birth are key events affecting this closure. An understanding of normal and failed hiatal closure is necessary to understand, manage, and prevent pelvic floor disorders. METHODS: This narrative review was conducted by applying the keywords "levator hiatus" OR "genital hiatus" OR "urogenital hiatus" in PubMed. Articles that reported hiatal size related to pelvic floor disorders and pregnancy were chosen. Weighted averages for hiatal size were calculated for each clinical situation. RESULTS: Women with prolapse have a 22% and 30% larger LH area measured by ultrasound at rest and during Valsalva than parous women with normal support. Women with persistently enlarged UGH have 2-3 times higher postoperative failure rates after surgery for prolapse. During pregnancy, the LH area at Valsalva increases by 29% from the first to the third trimester in preparation for childbirth. The enlarged postpartum hiatus recovers over time, but does not return to nulliparous size after vaginal birth. Levator muscle injury during vaginal birth, especially forceps-assisted, is associated with increases in hiatal size; however, it only explains a portion of hiatus variation-the rest can be explained by pelvic muscle function and possibly injury to other level III structures. CONCLUSIONS: Failed hiatal closure is strongly related to pelvic floor disorders. Vaginal birth and levator injury are primary factors affecting this important mechanism.