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Women less than six months postpartum, exclusively breastfeeding, or with prior midline abdominal surgery or hernia repair involving a midline incision or abdominoplasty were excluded. Inter-recti distance was measured at six predefined locations along the linea alba in the supine, knee-flexed resting position using ultrasound. For the analysis, the maximal IRD of each examinee across all sites was used.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      A total of 1,840 women with naturally occurring anatomy were examined. At the standard site 3\u00a0cm above the umbilicus, the mean IRD was 2.37\u00a0cm (SD 1.19\u00a0cm; range 0.35\u20139.86\u00a0cm). Nulliparous women had a lower mean IRD (1.52\u00a0cm, SD 0.70\u00a0cm; 0.35\u20134.37\u00a0cm,\n                      <jats:italic>n<\/jats:italic>\n                      \u2009=\u2009539) than parous women (2.71\u00a0cm, SD 1.18\u00a0cm; 0.46\u20139.86\u00a0cm,\n                      <jats:italic>n<\/jats:italic>\n                      \u2009=\u20091,301). The cohort\u2019s 80th percentile for IRD was 3.24\u00a0cm. Based on maximal IRD, 38.5% had IRD\u2009\u2265\u20093\u00a0cm and 5.4% exceeded 5\u00a0cm; the 95th percentile was 5.09\u00a0cm. Maximal IRD most often occurred at the level of the umbilicus (41.3%) or 3\u00a0cm above (44.1%) and rarely below the umbilicus. Maximal IRD correlated weakly with adiposity measures (body mass index (BMI) \u03c1\u2009=\u20090.227; waist \u03c1\u2009=\u20090.273; weight \u03c1\u2009=\u20090.199) and no correlation was observed with height. Regression analysis showed that each childbirth was associated with a 0.42\u00a0cm increase in maximal IRD, and BMI increased IRD by 0.061\u00a0cm per kg\/m\u00b2.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>IRD is a continuous anatomical characteristic exhibiting considerable normal variation among adult women. A maximal IRD of up to 5\u00a0cm may be regarded as being within the upper tail of the population reference distribution. Fixed cutoff values should be proportionate to clinical symptoms, in order to prevent unnecessary interventions. Altogether, our findings provide population-based reference data for interpreting IRD measurements.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1007\/s10029-026-03810-8","type":"journal-article","created":{"date-parts":[[2026,8,31]],"date-time":"2026-08-31T10:53:09Z","timestamp":1788173589000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Population-based ultrasound reference values for inter-rectus distance: threshold prevalence, percentiles, and the limitations of fixed cutoffs"],"prefix":"10.1007","volume":"30","author":[{"ORCID":"https:\/\/orcid.org\/0009-0005-0465-0128","authenticated-orcid":false,"given":"Annukka","family":"Marttila","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Katariina","family":"Kilpivaara","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jenni","family":"Kinnunen","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Susanna M","family":"Savukoski","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pasi P","family":"Ohtonen","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Riikka K","family":"Arffman","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lotta","family":"Vuokila","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marika H","family":"Kangasniemi","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kaisu","family":"Luiro","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Maria","family":"Rajecki","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tero","family":"Rautio","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Terhi T","family":"Piltonen","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,8,31]]},"reference":[{"key":"3810_CR1","doi-asserted-by":"publisher","first-page":"239","DOI":"10.1006\/jsre.2000.6071","volume":"96","author":"H Axer","year":"2001","unstructured":"Axer H, Keyserlingk DGV, Prescher A (2001) Collagen fibers in linea alba and rectus sheaths: II. 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Patient consent, consent to participate and for publication. Informed, written consent was obtained from all individual participants included in the study.","order":1,"name":"Ethics","label":"Ethics approval","group":{"name":"EthicsHeading","label":"Declarations"}},{"value":"All the authors declare that there are no known conflicts of interest.","order":2,"name":"Ethics","label":"Competing Interests","group":{"name":"EthicsHeading","label":"Declarations"}}],"article-number":"337"}}