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

Abstract

The purpose of this study was to describe levator ani (LA) anatomy in postterm nulliparas using 3-dimensional (3-D) magnetic resonance (MR). 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. 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. 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.