Table 1 Shows the results of the subgroups analysis

Time of administration

CB

VB

before surgery

after surgery

 < 5 min

 > 5 min

Total blood loss

MD = -2.29 mL, 95%CI [-3.49 to -1.10], P < 0.001; (I² = 69.72%)

[7, 24,25,26, 29, 32, 34, 37, 38, 45, 47,48,49, 54,55,56,57, 61,62,63,64,65, 68,69,70, 75]

MD = -1.38 mL, 95%CI [-2.29 to -0.48], P < 0.001; (I² = 48.08%)

[31, 39,40,41, 60, 71]

MD = -0.62 mL, 95%CI [-1.39 to 0.14], P = 0.65; (I² = 67.58%)

[18, 66, 73, 77]

MD = -1.21 mL, 95%CI [-2.10 to -0.32], P = 0.02; (I² = 57.18%)

[6, 27, 42, 50, 74, 76]

Change in HB

MD = 0.84, 95%CI [0.68 to 0.98], P < 0.001; (I² = 64.67%)

[24,25,26, 29, 32, 34, 38,39,40,41, 45, 48, 49, 54,55,56,57, 61,62,63,64,65, 68,69,70, 75]

MD = 1.32, 95%CI [1.21 to 2.26], P < 0.001; (I² = 58.12%)

[7, 31, 37, 47, 60, 71]

MD = -0.05%, 95%CI [-0.49 to 0.39], P = 0.65; (I² = 61.95%)

[18, 46, 77]

MD = 0.42%, 95%CI [0.21 to 0.63], P < 0.001; (I² = 45.88%)

[36, 42, 76]

Occurrence of PPH

OR = 0.28 mL, 95%CI [0.18 to 0.44], P < 0.001; (I² = 58.65%)

[24, 26, 28, 29, 34, 37, 47, 48, 54, 55, 64, 65, 69, 70, 75]

OR = 0.45 mL, 95%CI [0.29 to 0.72], P < 0.001; (I² = 66.82%)

[12, 35, 39, 41, 43, 52, 53, 60, 71]

OR = 0.81, 95%CI [0.65 to 1.01], P = 0.57; (I² = 0%)

[18, 46, 66, 77]

OR = 0.42, 95%CI [0.23 to 0.75], P = 0.01; (I² = 30.65%)

[27, 36, 50, 58, 74, 76]

Quality of included studies

Low risk of bias

Some concern

High risk of bias

Total blood loss

CB

MD = -0.75 mL, 95%CI [-1.28 to -0.22], P < 0.001; (I² = 58.19%)

[25, 34, 37, 38, 54, 60]

MD = -1.58 mL, 95%CI [-2.18 to -0.98], P < 0.001; (I² = 67.45%)

[24, 26, 31, 39,40,41, 47, 49, 55, 61, 64, 65, 69,70,71]

MD = -3.66 mL, 95%CI [-6.33 to -1.00], P < 0.001; (I² = 69.80%)

[7, 29, 32, 45, 48, 56, 57, 62, 63, 68, 75]

VB

(MD = -0.51 mL, 95%CI [-0.85 to -0.16], P = 0.01), high heterogeneity (I² = 61.91%)

[30, 42, 50, 73, 76, 77]

MD = -0.38 mL, 95%CI [-1.00 to -0.24], P = 0.65; (I² = 57.72%)

[66, 74]

MD = -1.96 mL, 95%CI [-3.50 to -0.41], P < 0.001; (I² = 67.88%)

[6, 18, 27]

Change in HB

CB

MD = 0.66%, 95%CI [0.29 to 0.97], P < 0.001; (I² = 54.39%)

[32, 48, 49, 60]

MD = 1.13%, 95%CI [1.05 to 1.36], P < 0.001; (I² = 62.03%)

[24,25,26, 29, 31, 37,38,39, 45, 47, 54, 61, 64, 65, 69,70,71, 75]

MD = 1.27, 95%CI [1.12 to 1.98], P < 0.001; (I² = 57.78%)

[7, 34, 40, 41, 55,56,57, 62, 63, 68]

VB

MD = 0.32, 95%CI [0.02 to 0.62], P = 0.01; (I² = 65.05%)

[42, 46, 50, 77]

MD = 0.31, 95%CI [0.14 to 0.49], P = 0.01; (I² = 0%)

[36, 76]

MD = -0.50, 95%CI [-0.81 to -0.18]

[18]

Occurrence of PPH

CB

OR = 0.52 mL, 95%CI [0.33 to 0.83], P < 0.001; (I² = 72.55%)

[34, 37, 52, 54, 60]

OR = 0.30 mL, 95%CI [0.19 to 0.46], P < 0.001; (I² = 52.33%)

[24, 26, 28, 35, 39, 41, 43, 47, 53, 55, 64, 65, 69,70,71]

OR = 0.21 mL, 95%CI [0.07 to 0.59], P = 0.001; (I² = 52.33%)

[12, 29, 48, 75]

VB

OR = 0.80, 95%CI [0.65 to 0.99], P = 0.04; (I² = 0%)

[46, 50, 76, 77]

OR = 0.26, 95%CI [0.13 to 0.54], P < 0.001; (I² = 0%)

[36, 58, 66, 74]

OR = 0.60, 95%CI [0.24 to 1.48], P = 0.70; (I² = 0%)

[18, 27]

Countries

HIC

UMIC

LMIC

Total blood loss

CB

MD = -0.28 mL, 95%CI [-0.49 to -0.07], P = 0.04; (I² = 64.18%)

[34, 60, 70]

MD = -0.47 mL, 95%CI [-0.60 to -0.33], P = 0.02; (I² = 0.00%)

[37, 61]

MD = -2.44 mL, 95%CI [-3.57 to -1.32], P < 0.001; (I² = 69.62%)

[7, 24,25,26, 29, 31, 32, 38,39,40,41, 45, 47,48,49, 54,55,56,57, 62,63,64,65, 68, 69, 71, 75]

VB

MD = -0.06, 95%CI [-0.12 to 0.01]

[77]

_

MD = -0.98 mL, 95%CI [-1.59 to -0.36], P < 0.001; (I² = 67.03%)

[6, 18, 27, 30, 42, 50, 66, 73, 74, 76]

Change in HB

CB

MD = 0.60, 95%CI [-0.27 to 1.47], P = 0.51; (I² = 56.59%)

[60, 70]

MD = 0.50, 95%CI [0.03 to 0.97], P = 0.01; (I² = 59.25%)

[32, 61]

MD = 1.12, 95%CI [1.02 to 1.38], P < 0.001; (I² = 65.22%)

[7, 24,25,26, 29, 31, 34, 37,38,39,40,41, 45, 47, 48, 54,55,56,57, 62,63,64,65, 68, 69, 71, 75]

VB

MD = 0.02, 95%CI [-0.05 to 0.08]

[77]

MD = 0.31, 95%CI [0.14 to 0.49], P = 0.01; (I² = 0%)

[36, 76]

MD = 0.21, 95%CI [-0.28 to 0.71], P = 0.65; (I² = 70.47%)

[18, 42, 46, 50]

Occurrence of PPH

CB

OR = 0.81, 95%CI [0.61 to 1.07], P = 0.28; (I² = 33.13%)

[34, 60, 70]

OR = 0.37, 95%CI [0.15 to 0.89]

[37]

OR = 0.27, 95%CI [0.19 to 0.38], P < 0.001; (I² = 39.65%)

[12, 24, 26, 28, 29, 35, 39, 41, 43, 47, 48, 52,53,54,55, 64, 65, 69, 71, 75]

VB

MD = 0.83, 95%CI [0.66 to 1.03]

[77]

MD = 0.25, 95%CI [0.09 to 0.67]

[36]

OR = 0.53, 95%CI [0.32 to 0.85], P = 0.03; (I² = 6.90%)

[18, 27, 46, 74, 76]