The levator hiatus (LH) is an anatomical opening within the pelvic floor, formed by the levator ani muscles and traversed by the urethra, vagina, and rectum. The minimal levator hiatus (MLH), comprising the narrowest region of this opening, is bordered by the pubococcygeus and puboanalis muscles anteriorly, puborectalis laterally, and the levator plate posteriorly. It plays a key role in vaginal support and pelvic floor integrity. Three-dimensional endovaginal ultrasound (3D EVUS) has enabled detailed visualization and measurement of MLH anatomy. While some studies suggest an inverse relationship between MLH size and pelvic floor muscle (PFM) strength, others find no significant correlation. The inconsistency in findings is particularly pronounced in postpartum populations, where obstetric factors such as prolonged labor, perineal trauma, or instrumental delivery may impact pelvic floor function. Given the limited and conflicting evidence, this study focuses on primiparous women to investigate whether MLH size is associated with PFM strength, and whether this relationship is influenced by obstetric risk factors for levator ani injury.

This is a cross-sectional analysis of data extracted from a previously completed single-site prospective cohort study conducted between 2012 and 2020. The study population included primiparous women over 18 years of age who had a term singleton vaginal delivery. Participants were stratified into high-risk and low-risk groups based on the presence of obstetric factors linked to levator ani injury. High-risk criteria included prolonged second-stage labor (>160 minutes), operative vaginal delivery, fetal head circumference >35.5 cm, or perineal laceration of second degree or higher. Low-risk participants had an intact perineum and no high-risk features. Exclusion criteria included prior incontinence or prolapse surgery, pelvic radiation, congenital reproductive tract anomalies, and pre-pregnancy pelvic floor symptoms.

All participants underwent 3D EVUS to measure MLH area (cm²) and Peritron™ perineometry to quantify PFM strength (mmHg) during maximal voluntary contraction, with both assessments performed 6 to 12 weeks postpartum. Statistical analysis included Student’s t-tests to compare MLH and PFM strength between risk groups. Pearson correlation was used to evaluate the association between MLH size and PFM strength overall and within each risk group. Multivariate regression analyses will be performed to evaluate if the relation between MLH and PFM strength changes with age, body mass index (BMI), and race.

Data collection  ongoing