RESUMEN
PURPOSE: The purpose of this study was to investigate the changes that occur in the levator ani muscle (1) during pregnancy and (2) after labor depending on the mode of delivery in a cohort of nulliparas. MATERIALS AND METHODS: A prospective cohort longitudinal study, consisting of 84 primiparas who were examined and recruited in an antenatal clinic was conducted. All participants were submitted to a real-time three-dimensional (3D) ultrasonographic evaluation of the levator ani at (1) 12, (2) 22, and (3) 32 weeks of pregnancy (4) and 4-6 months postdelivery. The 3D volumes were acquired and stored for an offline analysis. RESULTS: Data from 59 women with at least two measurements were available for analysis. 35 women were delivered vaginally and 24 via cesarean section. There was a statistical increase in the dimensions of the levator hiatus at each pregnancy trimester when compared to the measurements of the previous trimesters. After vaginal delivery, hiatal dimensions increased compared to the third-trimester measurements; after cesarean section, hiatal dimensions decreased. CONCLUSIONS: This study supports that in primiparas, the dimensions of the levator hiatus increase significantly during pregnancy and subsequently either increase further after vaginal delivery or decrease to the first-trimester levels after cesarean section.