(Poster 131) Pelvic Floor Morphology by 3D US in a Low vs. High-risk Obstetric Population

Objectives: Imaging studies characterizing levator ani muscle (LAM) injury after childbirth are limited. There is a strong positive correlation between vaginal prolapse stage and the minimal levator hiatus (MLH) measurement that can be seen on 3D Endovaginal Ultrasound (EVUS). Also, obstetric levator avulsion is associated with larger levator hiatus and wider genital hiatus after delivery based on the use of 3D transperineal US. EVUS studies of morphologic differences between high and low risk obstetric populations are lacking.

The objective is to examine the association between MLH on 3D EVUS and pelvic floor dysfunction after the first vaginal delivery in low-risk versus high-risk obstetric populations.

Methods: This was a single-site prospective cohort study of patients undergoing their first vaginal delivery between 2012 and 2020 at a university hospital. Subjects were categorized as high risk if they had a second degree or greater perineal laceration, a prolonged second stage of labor >160 min, instrumented delivery, or fetal head circumference >35.5cm. Women were classified as low risk if they had an intact perineum and no previously defined risk factors for LAM injury at vaginal birth.

Relevant obstetric information was obtained by chart abstraction. At the 6-week postpartum visit, a history was obtained, a pelvic organ prolapse quantification exam was performed, and an EVUS (9-16 MHz, 360° rotational 3D system) was obtained. Transaxial images were measured for total MLH area (mm3), length (mm), and width (mm). Patients also completed PFIQ-20 and PFDI-7 questionnaires at 12 weeks postpartum. T-tests and Spearman correlations were used to analyze data.

Results: 160 patients were consented and 129 were included in the analysis as they had complete data sets with completed survey questionnaires. Of the studied population, 59 patients (46%) were low risk and 68 (54%) were high risk. There was no difference in the MLH measurements between the high and low risk groups (p=0.16). When evaluating the correlation between MLH and pelvic floor dysfunction (PFIQ-7 and PFDI-20 scores) stratified by high and low risk, there were weak correlations (all p-values >0.05). The correlations between MLH area and total PFIQ and PFDI score in the high-risk group were 0.08 and -0.18, respectively. In the low-risk group, the correlations between MLH area and PFIQ and PFDI scores were 0.026 and 0.083, respectively.

Conclusions: In the postpartum period, there is no significant association between pelvic floor morphology (by MLH measurements on 3D EVUS) and pelvic floor dysfunction when stratified by low versus high-risk obstetric groups. MLH was not a predictor of pelvic floor dysfunction in women with high risk obstetric factors in the postpartum period.