Table 1.
Description of the studies included in the meta-analysis
| Author [Ref.] | Year | LoE | Study design | No. of subjects | Age, years (mean) | Fertility status | Menstrual phase | Probe upper MhZ limit | Method | Follicles description | Follicles: section vs. whole ovary | Artery sampled for Doppler analysis (PI) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Adali et al. [24] | 2009 | 3 | Prospective | 42 | 24.3 | Reproductive age | Follicular | 6.5 | 2D TV | NA | NA | Inside ovarian stroma, not close to surface or follicles |
| Adams et al. [25] | 2004 | 2 | Retrospective | 29 | 28.4 | Reproductive age | Follicular | 5.0 | 2D TA and TV | 2–8 mm | NA | NA |
| Ajossa et al. [26] | 2002 | 3 | Prospective | 15 | 29.5 | Reproductive age | Follicular | 7.0 | 2D TV | 2–8 mm | NS | NA |
| Alebić et al. [27] | 2018 | 3 | Retrospective | 705 | 33.4 | Reproductive age | follicular | 7.0 | 2D TV | 2–9 mm | Whole | NA |
| Allemand et al. [28] | 2006 | 3 | Retrospective | 29 | 30.9 | Reproductive age | Follicular | 8.0 | 2D and 3D TV | < 10 mm | Whole/section | NA |
| Assens et al. [29] | 2020 | 3 | Prospective | 115 | 16 | Reproductive age | Follicular | 8.0 | 2D and 3D TA | 2–8 mm | Whole | NA |
| Aviram et al. [30] | 2008 | 3 | Retrospective | 77 | NR | Menopausal | NA | NR | 2D TV | NA | NA | NA |
| Badouraki et al. [31] | 2008 | 3 | Prospective | 99 | 6.9 | Prepubertal | NA | 7.5 | 2D TA | NA | NA | NA |
| Bancsi et al. [32] | 2002 | Prospective | 120 | 34.9 | Reproductive age | Follicular | 7.5 | 2D TV | < 5 mm | NA | NA | |
| Basir et al. [33] | 2001 | 3 | Prospective | 20 | 33 | Reproductive age | Follicular | 7.0 | 2D TV | NA | NA | Within ovarian parenchyma, close proximity to follicles or c.l |
| Bath et al. [34] | 2003 | 3 | Retrospective | 11 | 23 | Reproductive age | Follicular | 4.0 | 2D TV | 2–10 mm | Whole | NA |
| Battaglia et al. (a) [35] | 2002 | 3 | Prospective | 10 | 6.9 | Prepubertal | NA | 3.5 | 2D TA | Small subcapsular | Whole | In the ovarian stroma at the max distance from the surface |
| Battaglia et al. (b) [35] | 2002 | 3 | Prospective | 15 | 7.6 | Prepubertal | NA | 3.5 | 2D TA | Small subcapsular | Whole | “ |
| Battaglia et al. [36] | 2006 | 3 | Prospective | 14 | 23.2 | Reproductive age | NR | 6.5 | 2D TV | Small antral | Whole | “ |
| Battaglia et al. [37] | 2012 | 3 | Prospective | 52 | 25.8 | Reproductive age | NR | 9.0 | 2D TV | Small subcapsular | Whole | “ |
| Bentzen et al. [38] | 2013 | 3 | Retrospective | 366 | 33.7 | Reproductive age | Follicular | 9.0 | 2D TV | 2–10 mm | Whole | NA |
| Carmina et al. [3] | 2005 | 3 | Prospective | 50 | 25.9 | Reproductive age | Follicular | NR | 2D TV | NA | NA | NR |
| Carmina et al. [39] | 2018 | 3 | Retrospective | 28 | 23.4 | Reproductive age | Follicular | 10.0 | 2D TV | 2–10 mm | Whole | NA |
| Catteau-Jonard et al. [40] | 2012 | 3 | Prospective | 95 | 29.0 | Reproductive age | Follicular | 7.0 | 2D TV | 2–9 mm | Whole | NA |
| Chan et al. [41] | 2006 | 3 | Retrospective | 70 | 36 | Reproductive age | NR | 7.0 | 2D and 3D TV | < 10 mm | Whole | NA |
| Chen et al. (a) [42] | 2008 | 3 | Retrospective | 26 | 17.85 | Reproductive age | Follicular | 6.0 | 2D TV | NA | NA | NA |
| Chen et al. (b) [43] | 2008 | 3 | Prospective | 153 | 27.15 | Reproductive age | Follicular | 6.0 | 2D TV | All countable follicles | Whole | NA |
| Christ et al. [44] | 2014 | 3 | Retrospective | 60 | 27 | Reproductive age | Follicular | 12.0 | 2D TV | 2–10 mm | Whole | NA |
| Christiansen et al. [45] | 2016 | 2 | Cross-sectional | 148 | 36.2 | Reproductive age | Follicular | 7.5 | 2D TV | 2–9 mm | Whole | NA |
| Çil et al. [46] | 2009 | 3 | Prospective | 25 | 33.04 | Reproductive | Follicular | 9.0 | 2D TV | 2–10 mm | Whole | Small artery in the ovarian stroma not close to the surface |
| Codner et al. [47] | 2006 | 3 | Prospective | 38 | 26.3 | Reproductive age | NR | 7.5 | 2D TA and TV | 2–9 mm | Section | NA |
| Dao et al. (a) [48] | 2019 | 3 | Retrospective | 55 | 7.5 | Prepubertal | NA | NR | 2D TA | NA | NA | NA |
| Dao et al. (b) [48] | 2019 | 3 | Retrospective | 93 | 14.7 | Reproductive age | NR | NR | 2D TA | NA | NA | NA |
| De Guevara et al. [49] | 2013 | 3 | Prospective | 35 | 37 | Reproductive age | Follicular | 7.5 | 2D TV | 2–9 mm | Whole | NA |
| Deb et al. [50] | 2013 | 3 | Prospective | 36 | 28.12 | Reproductive age | Follicular | 9.0 | 2D and 3D TV | 2–10 mm | Whole | NA |
| Dewailly et al. [51] | 2011 | 3 | Retrospective | 66 | 30 | Reproductive age | Follicular | 9.0 | 2D TV | < 10 mm | Whole | NA |
| Dumesic et al. [52] | 2001 | 3 | Cross-sectional | 25 | 30.8 | Reproductive age | Follicular | 8.0 | 2D and 3D TV | < 10 mm | Whole | NA |
| Elgindy et al. [53] | 2008 | 3 | Prospective | 33 | 30.19 | Reproductive age | Follicular | 6.5 | 2D TV | 2–10 mm | Whole | NA |
| Erdem et al. [54] | 2003 | 3 | Retrospective | 62 | 37.6 | Reproductive age | Follicular | 5.0 | 2D TV | < 8 mm | Whole | NA |
| Fruzzetti et al. [55] | 2015 | 3 | Cross-sectional | 72 | 13.7 | Reproductive age | Follicular | 10.0 | 2D TA and TV | NA | NA | NA |
| Fulghesu et al. [5] | 2001 | 3 | Retrospective | 30 | NR | Reproductive age | Follicular | 6.5 | 2D TV | NA | NA | NA |
| Fulghesu et al. [56] | 2006 | 3 | Prospective | 10 | 24.4 | Reproductive age | Follicular | 6.5 | 2D TV | Total no. of follicles | Section | NA |
| Golestani et al. (a) [57] | 2008 | 3 | Retrospective | 20 | 13.5 | Reproductive age | NR | 3.5 | 2D TA | NA | NA | NR |
| Golestani et al. (b) [57] | 2008 | 3 | Retrospective | 40 | 9.6 | Prepubertal | NA | 3.5 | 2D TA | NA | NA | NR |
| Greenwood et al. [58] | 2017 | 2 | Prospective | 226 | 33.1 | Reproductive age | Follicular | 8.0 | 2D TV | 2–10 mm | Whole | NA |
| Herter et al. [59] | 2002 | 3 | Prospective | 139 | 6 | Prepubertal | NA | 5.0 | 2D TA | NA | NA | NA |
| Homer et al. [60] | 2019 | 2 | Retrospective | 20 | 25.7 | Reproductive age | Follicular | 9.0 | 3D TV | 2–9 mm | Whole | NA |
| Jarrett et al. [61] | 2020 | 2 | Prospective | 12 | 30 | Reproductive age | Follicular | 12.0 | 2D and 3D TV | NA | Whole | NA |
| Järvelä et al. (a) [62] | 2002 | 3 | Prospective | 28 | 35 | Reproductive age | Follicular | 7.0 | 3D TV | 2–8 mm | NA | NA |
| Järvelä et al. (b) [63] | 2003 | 3 | Prospective | 29 | NR | Reproductive age | Follicular | 7.0 | 3D TV | Tot no. of follicles | Whole | NA |
| Järvelä et al. (c) [64] | 2007 | 3 | Prospective | 11 | 30.8 | Reproductive age | Follicular | 7.0 | 3D TV | NA | NA | NA |
| Jokubkiene et al. [65] | 2006 | 3 | Prospective | 14 | 28 | Reproductive age | Follicular | 10.0 | 3D TV | NA | NA | NA |
| Jokubkiene et al. [66] | 2012 | 3 | Prospective | 214 | 30 | Reproductive age | Follicular | 12.0 | 3D TV | 2–10 mm | Whole | NA |
| Jonard et al. [67] | 2005 | 2 | RCT | 57 | 29 | Reproductive age | NR | 7.0 | 2D TV | 2–9 mm | Whole | NA |
| Kline et al. [68] | 2004 | 4 | Prospective | 65 | 35 | Reproductive age | NR | 10.0 | 2D TV | All countable follicles | Whole | NA |
| Köşüş et al. [69] | 2011 | 3 | Prospective | 65 | 26.7 | Reproductive age | Follicular | 6.5 | 2D TV | All countable follicles | Whole | NA |
| Lam et al. [70] | 2007 | 3 | Prospective | 40 | 32.5 | Reproductive age | Follicular | 7.5 | 3D TV | 2–9 mm | Section | One of the main vessels with the ovarian stroma |
| Łebkowska et al. [71] | 2016 | 2 | cross-sectional | 16 | 24 | Reproductive age | Follicular | 9.0 | 2D TV | 2–9 mm | Whole | NA |
| Lie Fong et al. [72] | 2017 | 3 | Retrospective | 297 | 28.3 | Reproductive age | NR | 7.5 | 2D TV | 2–9 mm | Whole | NA |
| Lujan et al. [4] | 2013 | 3 | Prospective | 70 | 27 | Reproductive age | Follicular | 12.0 | 2D TV | 2–9 mm | Whole/section | NA |
| Merino et al. (a) [73] | 2019 | 3 | Retrospective | 53 | 13.9 | Reproductive age | Follicular | 5.0 | 2D TA | 2–9 mm | Section | NA |
| Merino et al. (b) [73] | 2019 | 3 | Retrospective | 22 | 14.3 | Reproductive age | Follicular | 5.0 | 2D TA | 2–9 mm | Section | NA |
| Murphy et al. [74] | 2006 | 3 | Prospective | 17 | 29.7 | Reproductive age | Follicular | 5.0 | 2D TV and TA | 2–10 mm | Section | NA |
| Orbak et al. [75] | 2007 | 3 | Retrospective | 55 | 0.01 | Prepubertal | NA | 7.5 | 2D TA | NA | NA | NA |
| Özay et al. [76] | 2019 | 3 | Prospective | 90 | 21.54 | Reproductive age | NR | 9.0 | 2D TV | NA | NA | In the ovarian stroma at the max distance from the surface |
| Ozkan et al. [77] | 2007 | 3 | Prospective | 43 | 20.8 | Reproductive age | Follicular | 6.0 | 2D TV | NA | NA | Ovarian stroma and in the wall of dominant follicle or c.l |
| Pan et al. [78] | 2002 | 3 | Prospective | 100 | 30.9 | Reproductive age | NR | NR | 3D TV | NA | NA | NA |
| Panidis et al. [79] | 2012 | 3 | Prospective | 254 | 31.3 | Reproductive | NR | NR | 2D TV | 2–9 mm | Whole | NA |
| Pascual et al. [80] | 2008 | 3 | Retrospective | 45 | 32.3 | Reproductive age | Follicular | 10.0 | 3D TV | 2–9 mm | Whole | NA |
| Peigné et al. [81] | 2018 | 3 | Case–control | 157 | 29 | Reproductive age | Follicular | 9.0 | 2D TV | 2–9 mm | Whole | NA |
| Pellizzari et al. [82] | 2002 | 3 | Case–control | 13 | 24.15 | Reproductive age | Follicular | 6.5 | 2D TV | NA | NA | Within the ovarian stroma |
| Petri Nahás et al. [83] | 2004 | 3 | Prospective | 30 | 36.66 | Reproductive age | NR | 7.5 | 2D TV | NA | NA | Ovarian artery in the pelvic infundibulum |
| Phy et al. [84] | 2004 | 4 | Prospective | 33 | 30.4 | Reproductive age | Follicular | 8.0 | 2D and 3D TV | 2–10 mm | Section | NA |
| Pirgon et al. [85] | 2015 | 3 | Case–control | 30 | 15.2 | Reproductive age | Follicular | 7.5 | 2D TV | 2–10 mm | Whole | NA |
| Pirwany et al. [86] | 2001 | 4 | cross-sectional | 14 | 31.2 | Reproductive age | Follicular | NR | NR | NA | NA | NA |
| Rosenfield et al. [87] | 2012 | 3 | Prospective | 19 | 24.5 | Reproductive age | Follicular | 9.0 | 2D TA and TV | 2–9 mm | NA | NA |
| Santoro et al. (a) [88] | 2003 | 4 | Prospective | 14 | NR (> 45) | Reproductive age | Follicular | 5.0 | 2D TV | < 10 mm | Whole | NA |
| Santoro et al. (b) [88] | 2003 | 4 | Prospective | 22 | NR | Reproductive age | Follicular | 5.0 | 2D TV | < 10 mm | Whole | NA |
| Sanverdi et al. [89] | 2018 | 4 | Cross-sectional | 139 | 31.04 | Reproductive age | Follicular | NR | 2D TV | AFC | Whole | NA |
| Sasaki et al. [90] | 2019 | 3 | Retrospective | 118 | 32.66 | Reproductive age | Follicular | 7.0 | NR | AFC | Whole | NA |
| Scheffer et al. (a) [91] | 2003 | 3 | Prospective | 49 | NR | Reproductive age | Follicular | 7.5 | 2D TV | 2–10 mm | Whole | NA |
| Scheffer et al. (b) [91] | 2003 | 3 | Prospective | 53 | NR | Reproductive age | Follicular | 7.5 | 2D TV | 2–10 mm | Whole | NA |
| Scheffer et al. (c) [91] | 2003 | 3 | Prospective | 60 | NR | Reproductive age | Follicular | 7.5 | 2D TV | 2–10 mm | Whole | NA |
| Shahrami et al. [92] | 2016 | 4 | Cross-sectional | 53 | 27.23 | Reproductive age | Follicular | NR | NR | NA | NA | NA |
| Shen et al. [93] | 2008 | 3 | Prospective | 23 | 31 | Reproductive age | Follicular | 9.0 | 2D TV | NA | NA | Large vessel at ovarian hilum |
| Singha et al. [94] | 2015 | 4 | Cross-sectional | 52 | 37 | Reproductive age | NR | 8.0 | 2D TV | NA | NA | NA |
| Su et al. [95] | 2008 | 4 | Cross-sectional | 18 | 45 | Reproductive age | Follicular | NR | 2D TV | 2–10 mm | Whole | NA |
| Taponen et al. [96] | 2004 | 2 | Retrospective | 58 | 31 | Reproductive age | NR | 6.0 | 2D TV | 2–8 mm | Section | NA |
| Tomioka et al. [97] | 2018 | 3 | Prospective | 11 | 30 | Reproductive age | Follicular | 10.0 | 2D TA and TV | 2–10 mm | Whole | NA |
| van Hooff et al. [98] | 2000 | 3 | Prospective | 58 | 16.4 | Reproductive age | Follicular | 5.0 | 2D TA | NA | NA | NA |
| Weerakiet et al. [99] | 2007 | 3 | Cross-sectional | 21 | 33.81 | Reproductive age | Follicular | 7.5 | 2D TV | < 10 mm | Whole | NA |
| Wongwananuruk et al. [100] | 2018 | 3 | Prospective | 63 | 29.7 | Reproductive age | Follicular | 8.0 | 2D TV or TR | 2–9 mm | Whole/section | NA |
| Younis et al. [101] | 2011 | 3 | Prospective | 101 | 28.76 | Reproductive age | Follicular | 9.0 | 2D TV | 2–9 mm | Whole | Stromal ovarian blood flow |
| Zhang et al. [102] | 2013 | 3 | Case–control | 685 | 26.56 | Reproductive age | NR | NR | 2D TV | 2–9 mm | Whole | NA |
LoE level of evidence according to the Oxford Centre for Evidence-Based Medicine, NA not applicable, NR not reported, PI pulsatilty index, TA transabdominal, TV transvaginal, 2D two-dimensional, 3D three-dimensional