DATASET FOR STUDY: Reliability and Agreement of Digital Calliper and Ultrasound Measurements for Inter-Recti Distance in Postpartum Women

Purpose: To determine test-retest reliability and agreement of digital calliper and ultrasound measurements of inter-recti distance (IRD) in postpartum women and examine associations with palpation. Methods: Thirty healthy primiparous women (8–16 weeks postpartum) completed two sessions separated by three days. IRD was assessed during a standardized abdominal contraction at 4.5 cm above the umbilicus, at the umbilicus, and 4.5 cm below the umbilicus using palpation, a digital calliper, and ultrasound (Mindray M8). Three repeated measures per site were averaged for each method. Test–retest reliability was evaluated with paired t-tests, intra-class correlation ICC, typical error (TE), and coefficient of variation (CV). Agreement between calliper and ultrasound was examined using t-tests, ICC, TE/CV, and Bland–Altman analysis with regression-based assessment of proportional bias. Results: No systematic between-visit differences were observed (all p > 0.24). Test–retest reliability was excellent for both methods (ICC = 0.94–0.98), with low error (TE = 0.09–0.13 cm; CV = 2.9%–4.4%). Agreement between methods was good-to-excellent (ICC = 0.78–0.96; TE = 0.12–0.30 cm), with the lowest agreement below the umbilicus at Visit 1. Ultrasound yielded slightly higher values, reaching significance above the umbilicus (bias −0.081 to −0.068 cm). Bland–Altman analysis showed minimal systematic bias and no proportional bias. Palpation correlated strongly with both instrument-based measures (r = 0.641–0.920; p < 0.001). Conclusions: Callipers and ultrasound provide reliable IRD assessment, with relatively small difference between the methods.