Effects of posture and anatomical location on inter-recti distance measured using ultrasound imaging in parous women

Study Design: Cross-sectional repeated measures.

Objectives: To quantify the effects of posture and measurement site on the inter-recti distance (IRD) and investigate the reliability of IRD measurement using ultrasound imaging in different postures. Background: The linea alba connects the rectus abdominis muscles anteriorly and the width is known as the IRD. The IRD is usually measured in crook-lying and is the primary outcome measure to assess for a divarication of recti abdominis (DRA). The effects of posture and measurement site on the IRD have not been investigated.

Methods: Ultrasound imaging was used to measure IRD in 41 women ≥8 weeks postpartum. The IRD was measured at three sites (superior-umbilicus, umbilicus and inferior-umbilicus), in three postures (crook-lying, sitting and standing), and repeated one-week later. The effects of posture and site were investigated using one-way ANOVAs. Reliability was analysed using Intraclass correlation coefficients (ICCs), Bland Altman analyses, standard error of measurement and minimal detectable change.

Results: The IRD was wider when standing vs. lying at both the superior-umbilicus and umbilicus by 0.30cm (95% CI 0.21 to 0.39) and 0.20cm (0.11 to 0.30) respectively (p<0.001). Measurements at the inferior-umbilicus were, on average, 1.6 and 2.1cm narrower than superior-umbilicus and umbilicus sites, respectively (p<0.001). There was high intra-rater reliability within-session (ICC3.3) and between-session (ICC3.1) at all sites measured.

Conclusion: The IRD can be measured reliably at all sites and postures. The IRD is wider at superior-umbilicus and umbilicus when upright compared with lying. There is a difference in IRD between all sites measured.