Table 1.

Grading criteria of SV morphology; Shanghai, China, 2020–2021.

Morphology of SV	Grading
Illustrations
Tortuosity	T1	T2	T3
	No obvious tortuosity	Tortuous veins or accompanied by prolonged veins	The veins are tortuous and prolonged, with branches like tree branches
Trunk-length	L1	L2	L3
	$\frac{{\mathrm{a}}_1+{\mathrm{a}}_2}{2}<\frac{3}{5}\times \mathrm{b}$ The length is shorter than 3/5 of the line between sublingual caruncle and tip of the tongue	$\frac{{\mathrm{a}}_1+{\mathrm{a}}_2}{2}=\frac{3}{5}\times \mathrm{b}$ The length is approximately 3/5 of the line between sublingual caruncle and tip of the tongue	$\frac{{\mathrm{a}}_1+{\mathrm{a}}_2}{2}>\frac{3}{5}\times \mathrm{b}$ The length is longer than 3/5 of the line between sublingual caruncle and tip of the tongue
Width	W1	W2	W3
	The maximum width of the vein is less than 3 mm	The maximum width of the vein is 3 ~ 4 mm	The maximum width of the vein is more than 4 mm

SV sublingual veins.