Appearance of the levator ani muscle in pregnancy as assessed by 3-D MRI

Objective: The purpose of this study was to describe levator ani (LA) anatomy in postterm nulliparas using 3-dimensional (3-D) magnetic resonance (MR). Study design: Nulliparas (n = 84) with uncomplicated, postterm pregnancies underwent an MR (4 mm slices, 0 gap) of the uterus and pelvis. LA volume and morphometry were assessed using 3-D post-processing software. Results: LA insertion into the symphysis was visible in 93%, and the iliococcygeus muscle assumed a convex shape (arch) in the 92% of the 84 women. The LA shape was characterized as "U" in 53% and "V" in 47%. Mean LA volume was 13.5 (3.7) cm³. There was a positive association between LA volume and higher fetal station (P = .02) and increasing BMI (P < .001). However, no relationship between LA volume and station was found after adjusting for BMI. Conclusion: BMI was correlated with LA volume in postterm nulliparas. LA insertion into the symphysis and the iliococcygeus arch were well-preserved overall and morphometry was variable.