Table 3.

Characteristics of the examiners, ultrasonographic imaging (USI) systems, and inter-recti distance (IRD) measurement methods in 49 study protocols

	Examiner’s profession and experience	Ultrasonographic scanner and transducer	IRD measurement site	Use of cutoff values for “normal” IRD or DRA	Number of images per site	Methods of image processing and measurement
Abuín-Porras 2019 (Spain) [42]	PT with USI experience	LOGIQ S7, XDclear, GE Healthcare; Little Chalfont, UK; 10- to 13-MHz linear probe, 55 mm; B-mode	just under the navel	Not applicable	Mean IRD of 3 images	Offline measurement with ImageJ software (Research Services Branch, National Institute of Health, Bethesda, MD, USA)
Arranz-Martín 2022 (Spain/ Canada) [74]	A women’s health PT with > 5 yr of experience in abdominal and perineal USI	Mindray 7; 12-MHz 30-mm linear probe (Mindray L14-6NS, Shenzhen, China); B- mode	2 cm below and above the navel center, the midpoint between the navel center and xiphoid	Not applicable; LA distortion assessment	Mean IRD of 2 images per site and task	measurement with digital caliper
Balasch-Bernat 2021 (Spain) [56]	Two PTs with 10 yr of clinical experience in women’s health and rehabilitative USI	Samsung HS30, (Samsung Medison co., LTD, Gangwon-do, Korea); linear probe LN 5–12; B-mode; panoramic mode*	2 cm above the superior navel border and 2 cm below the inferior navel border	Not applicable	Mean IRD of 3 images per site and task	Not specified
Barbosa 2013 (Brazil) [60]	Not specified	Medison SonoAce 8000, Korea; 5- to 7-MHz linear probe	3, 6, 9, 12 cm above the navel	Not applicable	Not specified	Not specified
Beamish 2019 (Canada) [8]	PT with postgraduate training, > 400-h experience in B-mode USI of the abdominal muscles (two PT students after 10-h training and 10-h practice made offline measurements, intrarater reliability: ICC = 0.96–0.98, interrater reliability: ICC = 0.94–0.95	SuperSonic Aixplorer UltraFast (SuperSonic Imagine, Aix-en-Provence, France); 10-MHz linear probe (SL15-4); B-mode; shearwave elastography	3 and 5 cm above and at the superior navel border	DRA = IRD > 22 mm at 3 cm above the umbilicus, DRA = mean IRD > 22 mm across 3 sites; LA stiffness and distortion assessment	Mean IRD of 3 images per site and task	Video and image capturing; image processing with the SuperSonic Aixplorer software
Belo 2020 (Brazil) [61]	Examiner who was previously trained	Philips HD3xe; 5- to 9-MHz linear probe	3 cm above, 2 cm below, and at the navel	DRA = IRD > 22 mm at 3 cm above, > 16 mm at 2 cm below, and > 20 mm at the navel	mean IRD of 3 images	Not specified
Benjamin 2020 (Australia) [67]	PT after a 2-h ultrasonography training session by an experienced sonographer; 16 h of practice in USI of IRD	GE Voluson I; 3- to 8-MHz linear probe, 38.1 mm (9 L)	4.5 cm above and at the upper border of the navel, 4.5 cm below and at the lower border of the navel	DRA = IRD > 22 mm;  ≥ 2 fingers width	2 images	Offline measurement
Castellanos-López 2022 (Spain) [57]	An expert in USI with several specialization courses and 5 yr of experience	LOGIC F6, GE Healthcare, Chicago, IL, USA); 6- to 13-MHz linear probe, B-mode	Same as Chiarello (2013) [62]	Not applicable	Not specified	Not specified
Chiarello 2013 (USA) [62]	Examiner with advanced training and 7 yr of clinical USI use; intrarater within-session reliability: ICC = 0.90–0.98	LOGIQ Book XP, GE Healthcare, Waukesha, WI; 5- MHz curvilinear probe; B-mode	4.5 cm above and below the navel midpoint	Not applicable	Not specified	On-screen measurement
Chiarello 2016 (USA) [9]	same as Chiarello (2013) [59]	same as Chiarello (2013) [62]	Same as Chiarello (2013) [62]	Not applicable	Not specified	Same as Chiarello (2013) [62]
Coldron 2008 (UK) [16]	Not specified	SSD, Aloka Co. Ltd., Mitaka-shi, Tokyo, Japan; 5-MHz linear probe (11-cm footprint)	Bottom transducer edge placed just cephalad to the navel	Not applicable	Mean IRD of 2 images	Offline measurement with on-screen calipers using USICA software, Dept. of Medical Physics, St. George’s Hospital, London
Corvino 2019 (Italy) [10]	Two operators with 33 and 13 yr of experience with USI, respectively. The operators had specific training in evaluating DRA	Voluson E8, GE Healthcare, and RS85 Samsung Healthcare; broadband probes, typically 10-MHz; for DRA > 4 cm: trapezoid, DRA > 5 cm: extended field of view*	3 cm above and below the navel (entire midline checked to identify the DRA pattern)	DRA = IRD > 20 mm at rest; DRA patterns: only above or below the navel, at the navel level, along the entire midline but wider above or below the navel	Mean IRD of 3 images per site	not specified
Crommert 2021 (Sweden) [68]	Not specified	LOGIQ-e R7, GE, Boston, MA; 12-MHz linear probe, 47 mm; B-mode; panoramic function*	4.5 cm above the navel center	increased IRD = IRD ≥ 2 fingers width	Mean IRD of 3 images	Offline analysis with custom-written script in MATLAB (MATLAB R2019a, MathWorks, Natick, MA, USA)
Da Cuña-Carrera 2021 (Spain) [11]	PT with knowledge of USI and experience in IRD measurement	SonoSite M-Turbo; 5- to 10-Mz linear probe; B-mode	Just above the navel (U point), halfway between the U point and xiphoid	Not applicable	Not specified	Frozen image on-screen measurement with transversal caliper
Depledge 2021 (New Zealand) [64]	PT experienced in USI, participated in a reliability study on IRD measurement with USI, ICC > 0.91 (Iwan, 2014 [44])	Philips iU22; 4- to 12-MHz linear or 4- to 9-MHz curvilinear probe (Philips Med. Syst. Co., Eindhoven, NL); B-mode	Same as Mota (2012) [49]	DRA = IRD > 2 fingers width	Mean IRD of 2 images	Not specified
Eisenberg 2021 (Israel) [27]	A physician specializing in gynecological USI	Voluson 730, GE Medical Systems, Zipf, Austria; probe not specified	Upper margin of the navel, 3 cm above, and 2 cm below the navel	DRA = IRD ≥ 22 mm at 3 cm above the navel, ≥ 20 mm at the upper margin of the navel, and/or ≥ 16 mm at 2 cm below the navel	Not specified	ARCHIVED data sets were analyzed using the proprietary software 4-D VIEW (GE Medical Systems)
Fan 2020 (Italy and Canada) [12]	PT with 5-yr experience in musculoskeletal USI	Esaote MyLab Seven (Esaote SpA, Genova, Italy); 6- to 18-MHz linear probe, 37 mm	2 cm above the navel	Not applicable	Not specified	Not specified
Q	PT with specific training in image capturing and measuring IRD	LOGIQ-e, GE; 4- to 12-MHz linear probe, 39 mm; B-mode	2 cm below the navel center	DRA = IRD > 16 mm at 2 cm below the navel center	Not specified	Images exported in DICOM format, processing as by Mota (2012)
Gillard 2018 (UK) [63]	PT, > 12mo of experience in USI, training on a national medical US society program; within- and between-session intrarater reliability: ICC = 0.90–0.99	Mindray DP50; 5-MHz linear probe, 53 mm (75L53 EA); B-mode	One-third of the xiphoid-navel distance, just superior to the navel, half of the navel-pubis distance	Not applicable	Mean IRD of 2 images per site and postural position	Offline measurement on JPEG images with bespoke MATLAB image processing software (ver. 7.1)
Gluppe 2020 (Norway) [13]	PT after specific training in USI of the pelvic floor and abdomen	LOGIQ-e R7, GE Healthcare; 5- to 13-MHz wideband linear probe, (GE > 12L-RS); panoramic mode*	2 cm above and below the navel center	DRA = IRD ≥ 2 fingers width, protrusion during curl-up; IRD ˃ 25 mm at 2 cm above/below navel	1 image per site and condition	Offline analysis with software program (MicroDicom)
He 2021 (China) [65]	A senior radiologist with 10 yr of experience in abdominal and musculoskeletal USI	Aixplorer; linear probe (SL10-2), Supersonic Imagine, FR); B-mode	Subxiphoidal, epigastric, umbilical, infraumbilical, suprapubic (International Endohernia Society, Reinpold, 2019 [24])	DRA = IRD ≥ 2 fingers width (in crook lying, arms crossed over the chest); DRA patterns: same as Corvino (2019) [10]	Not specified	Measurements with an on-screen caliper
Hills 2018a (Canada) [53]	PT with postgraduate training in musculoskeletal USI and > 50 h of experience in USI of the abdominal muscles	Voluson-i (GE Healthcare, Mississauga, Ontario, Canada); 10-MHz linear probe, 53 mm (9L-RS); B-mode; trapezoid mode*	3 and 5 cm above the navel	DRA = IRD > 20 mm	2 images per probe position and task	Offline measurement using Image J, version 1.46r (National Institutes of Health, Bethesda, MD, USA)
Hills 2018b (Canada) [17]	PT with postgraduate training in musculoskeletal USI, > 100 h of experience in USI of the abdominal muscles	Same as Hills (2018a) [53]	Superior navel border; 3 and 5 cm above the navel	DRA = IRD > 22 mm at 3 cm above navel and at least one other site; mean IRD of 3 sites > 20 mm	Mean IRD of 3 images per site	As by Hills (2018a) [53]
Iwan 2014 (New Zealand) [47]	PT, 8-yr practice in USI and 4th-yr PT student after 2- × 2-h training in USI of the abdominal anatomy and IRD measurement; intrarater reliability: within-session: ICC = 0.91–0.98 for PT, ICC = 0.89–0.98 for PT student; between-session: ICC = 0.79–0.98 for PT, ICC =  − 0.51 to 0.88 for PT students	Low resolution: Chison 8300 Deluxe (Chison Medical Imaging Co. Ltd., China), 7.5-MHz linear probe; high-resolution: Phillips iU22 (Royal Philips Electronics, the Netherlands), 12.5-MHz linear probe	2 cm above and below the navel	Not applicable	2 images per condition per researcher	Measurement using the digital caliper setting on the USI unit
Keshwani 2015a (Canada) [48]	PT after 16 h of formal training on musculoskeletal USI; > 100 h of clinical USI experience; trained on IRD measurement by a USI expert; intrarater between-session reliability: ICC = 0.95–0.99	Voluson i (GE Healthcare, Waukesha, WI), 3- to 10-MHz linear probe; MyLab Five (Esaote SpA, Genoa, IT), 4- to 13-MHz linear probe; acoustic standoff pad 2 × 4 cm (ATS Lab., Inc., Bridgeport, CT)*	5 and 3 cm above and at the superior border of the navel, 3 cm below the inferior border of the navel	DRA = IRD ≥ 2 fingers width at the navel (in hook lying, neck flexed)	Mean IRD of 5 images per site and condition	Offline measurement using ImageJ (National Institutes of Health, Bethesda, MD) and software with the MyLab Five system (Esaote SpA)
Keshwani 2015b (Canada) [54]	Investigator after 16 h of formal training in USI of the abdominal muscles and > 200 h of experience in IRD evaluation with USI; 20 h of experience in extended field-of-view use; between-trial reliability for conventional, standoff pad, and panoramic techniques: ICC = 0.98–0.99	LOGIQ-e, GE Healthcare, Waukesha, WI; 4- to 13-MHz linear probe, 12.7 × 47.1 mm; B-mode; acoustic standoff pad (15 × 10 × 2 cm), ATS Lab., Bridgeport, CT; panoramic mode	Superior umbilical border	Not applicable	Mean IRD of 5 images per each method	Offline measurement using ImageJ Version 1.48, National Institutes of Health, Bethesda, MD
Keshwani 2016 (Canada) [55]	Two PTs after a 16-h course in USI. Rater 1: > 100 USI evaluations of IRD; Rater 2: 10 h of training from Rater 1; interrater reliability: ICC = 0.63–0.96	Voluson i, GE Healthcare, Chalfont St. Giles, UK; 3- to 10-MHz linear probe; B-mode; acoustic standoff pad 2 × 4 cm, ATS Lab., Bridgeport, CT*	Same as Keshwani (2015a) [48]	Not applicable	Mean IRD of 5 images per site, task, and rater (mean of at least 2 images in case of poor image quality)	Offline measurement using ImageJ, National Institutes of Health, Bethesda, MD, USA
Keshwani 2018 (Canada) [20]	Registered sonographer with specific training in the measurement approach	LOGIQ-e, GE, Buckinghamshire, UK; 5- to 13-MHz linear probe; B-mode; panoramic mode*	Same as Keshwani (2015a) [48]	DRA = IRD ≥ 2 fingers width at all sites (in crook lying, head lifted off pillow)	Mean IRD of 5 images in each site	Not specified
Keshwani 2019 (Canada) [33]	Registered sonographer with > 15 yr of experience in gynecological, obstetrical, and musculoskeletal USI; > 30 h of training on the USI protocol	LOGIQ-e, GE; 4- to 13-MHz linear probe, 12.7 × 47.1 mm; B-mode; panoramic imaging*	Same as Keshwani (2015a) [48]	DRA = IRD ≥ 2 fingers width at all sites (in crook lying, head lifted off pillow)	Mean IRD of 5 images per site	Not specified
Kim 2022 (Korea) [69]	Not specified	MySono U5, Samsung Medison, Seoul, Korea, 2010; elliptical probe, B-mode, 47–63 Hz	2.5 cm above the top of the navel	DRA = IRD ≥ 2 fingers width—self-examination, verified by USI	Not specified	Measurements made with the caliper of the ultrasound apparatus
Lee 2016 (Australia and Canada) [34]	Not specified	MyLab 25, Esaote SpA, Genoa, Italy; 12-MHz linear probe; B-mode	Just above the navel (U point), halfway between the U point and xiphoid	DRA = IRD > 22 mm at 3 cm above the navel, DRA = IRD > 15 mm inferior to xiphoid; LA distortion index: the average amount of deviation of the LA path from the shortest path between its attachments	3 images per site and condition	Images captured from videos, exported to JPEG format; analyzed using ImageJ (National Institutes of Health, Bethesda, MD, USA)
Li 2022 (China) [66]	Three physicians, each with 12 yr of clinical experience	Voluson E10 (GE Healthcare, Milwaukee, WI, USA); 5- to14-MHz linear probe (ML6-15-D)	3 cm above, below, and at the navel	Not applicable	Not specified	Not specified
Liaw 2011 (Taiwan) [18]	PT with 13 yr of experience, 5 yr of assessing abdominal muscles using USI; interimage reliability: ICC = 0.91–0.97	SSD-550, Aloka Co, Tokyo, Japan; 7.5-MHz linear probe, 38 mm; B-mode	Probe lower edge: 2.5 cm above and at the upper margin of the navel, probe upper edge: 2.5 cm below and at the lower margin of the navel	Not applicable	Mean IRD of 3 images per site	Measurement with an on-screen caliper
Mota 2012 (Portugal and Norway) [49]	PT trained in IRD evaluation with USI; discussed the USI protocol and analysis, and practiced with an experienced radiologist. Intra-image reliability: ICC > 0.90, intrarater between-day reliability: ICC = 0.50–0.90	LOGIQ-e, GE Healthcare, Waukesha, WI, USA; 4- to12-MHz linear probe, 39 mm; B-mode	The bottom edge of the probe at 2 cm above and below the navel center	Not applicable	1 image per site and condition	Offline processing using a customized program, MATLAB image processing software (MathWorks, Inc., Natick, MA); images assumed as a pixel-based coordinate system
Mota 2013 (Portugal and Norway) [71]	PT trained by an experienced radiologist	GE LOGIQ-e; 4- to 12-MHz linear probe, 39 mm; B-mode	Same as Mota (2012) [49]	Not applicable	Not specified	JPG images, processing as by Mota (2012) [49]
Mota 2015 (Portugal and Norway) [35]	PT with specific training in USI, including 3 yr of experience assessing IRD	LOGIQ-e; GE Healthcare, Waukesha, WI; 4- to 12-MHz linear probe, 39 mm (fixed frequency of 12 MHz); B-mode	The bottom edge of the probe at 2 and 5 cm above and 2 cm below the navel center	Not applicable	1 image per site and condition	DICOM images, offline analysis using a customized program (MATLAB Image Processing Toolbox) as by Mota (2012) [49]
Mota 2018 (Portugal and Norway) [72]	PT with specific training in USI, including experience in assessing IRD; discussed and practiced the USI protocol and analysis with an experienced radiologist	LOGIQ-e, GE Healthcare, Waukesha, WI, USA; 12-MHz linear probe, 39 mm; B-mode	Same as Mota (2015) [35]	Determined “normal” IRD values at 5 and 2 cm above, 2 cm below the navel: at 35–41wk gestation: up to 79, 86, and 79 mm, respectively; at 24–26wk postpartum: up to 24, 28, and 21 mm, respectively	1 image per site	DICOM images, processing as by Mota (2012) [49]
Morales 2018a (Spain) [43]	PT with 3 yr of rehabilitative USI experience	Toshiba Aplio 500 Platinum, Toshiba American Medical Systems; CA, USA; 7- to 14-MHz linear probe, 40 mm (18L7PLT-1204BT); B-mode	Just under the navel	Not applicable	Mean IRD of 3 images	Offline measurement using ImageJ software (version 2.0; US National Institutes of Health, Bethesda, MD, USA)
Morales 2018b (Spain) [58]	PT with 3 yr of USI experience	LOGIQ S7, GE Healthcare, UK; 3.1- to 10-MHz linear probe, 44 mm (9L-D); B-mode	Same as Morales (2018a) [43]	Not applicable	Same as Morales (2018a) [43]	Offline measurement as by Morales (2018a) [43]
Nanikawa 2021 (Japan) [50]	PT accustomed to USI, after sufficient practice; intrarater reliability: within-day, ICC = 0.99; between-day, ICC = 0.98	Noblus, Hitachi, Ltd., Tokyo, Japan; linear L64 probe (5- to 18-MHz); B-mode	Below the navel	Not applicable	Mean IRD of 2 images	Not specified
Pascoal 2014 (Portugal) [36]	not specified	Sonoline Prime SLC, Siemens, Erlangen, Germany; 7.5-MHz linear probe, 60 mm; B-mode	lower border of the probe: just cephalad to the navel (approximately 2 cm above the navel center)	Not applicable	Not specified	Images recorded on mini DV tape, converted to JPG; semi-automated offline analysis as by Mota (2012) [49]
Romero-Morales 2018 (Spain) [59]	Not specified	LOGIQ P7, GE Healthcare; UK; 4- to 13-MHz linear probe, 38 mm (L6-12-RS)	same as Morales (2018a) [43]	Not applicable	SAME as Morales (2018a) [43]	ImageJ software (version 2.0) used for offline analysis
Romero-Morales 2019 (Spain) [44]	PT with 3 yr of experience in USI of the musculoskeletal field	LOGIQ, GE, Healthcare, UK; 4- to 13-MHz linear probe, 38 mm	Same as Morales (2018a) [43]	Not applicable	same as Morales (2018a) [43]	ImageJ software (Bethesda, MD, USA) used for offline measurement
Romero- Morales 2020 (Spain) [45]	PT with 5 yr of USI experience	LOGIQ R S7 R3 XDclear, GE Healthcare, Milwaukee, WS, USA; 5- to 15-MHz linear probe, 44 mm (GE ML6–15); B-mode	Just above the navel (according to the photo and its legend)	Not applicable	Same as Morales (2018a) [43]	Measurement using ImageJ software (version 2.0; US National Institutes of Health, Bethesda, MD, USA)
Sancho 2015 (Portugal and Norway) [73]	PT trained in image capturing and IRD measurement	LOGIQ-e; GE Healthcare, Hatfield, UK; 4- to 12-MHz linear probe, 30 mm; B-mode	2 cm above and below the navel center	Not applicable	The best of 3 images (per condition and site)	images imported in JPG format; offline semi-automated analysis as by Mota (2012) [49]
Starzec-Proserpio 2022 (Poland) [70]	Two experienced women’s health PTs trained in the musculoskeletal USI; attended a half-day training together to promote consistency and avoid bias throughout the data collection process	Voluson P6 (GE Healthcare Syst.; Chicago, IL, USA); 4- to 12-MHz, 37-mm linear probe; palpation + caliper used to measure IRD wider than the probe	2 cm above the navel	Not applicable	Not specified	The measuring feature was used: after capturing the image, an on-screen cursor was used to mark the IRD
Theodorsen 2019 (Norway) [37]	PT after specific training in USI of the pelvic floor and abdomen	Mindray M7; 5- to 10-MHz linear probe	Lower edge of the probe at 2 cm above and below the navel center	DRA = IRD ≥ 2 finger widths at or 2 cm above/below the navel; protrusion	1 image per site and condition	Image in digital format processing; use of ultrasound’s integrated measurement tool
Theodorsen 2022** (Norway) [75]	Women’s health PT with 21 yr of clinical experience; with specific training and clinical experience in USI of the pelvic floor and abdomen	Alpinion EC8 Diamond; 8-17 MHz linear probe, B-mode	Lower edge of the probe 2 cm above and below the navel	DRA = IRD ≥ 28 mm at the navel level and/or 2 cm above and below the navel (at rest) and/or abdominal protrusion	Not specified	JPG images will be transferred to a server and the measurements will be performed using MicroDicom software
Whittaker 2013 (UK and Canada) [46]	PT with 10 yr of USI experience; within- and between-day intrarater reliability of IRD measurement: ICC = 0.99	MyLab 25, Esaote North America, Inc., Indianapolis, IN; 5.0-MHz curvilinear probe, 40 mm, resolution: 1.0 mm (lateral), 0.93 mm (axial); B-mode	Just inferior to the navel	Not applicable	Mean IRD of 3 images	Offline measurement using MATLAB Ver. 7.1 software, MathWorks, Inc., Natick, MA; in consultation with a video clip of IRD

^*This procedure/mode was used when IRD was too large to be visualized on conventional USI. **Registered study protocol (presenting research project). PT: physiotherapist; DRA: diastasis recti abdominis; LA: linea alba; DICOM: Digital Imaging and Communications in Medicine