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Table 3 Gestational age-defined reference ranges for MCA S/D to UA S/D ratio

From: Ultrasound angiology reference standards of fetal cerebroplacental flow in normal Egyptian gestation: statistical analysis of one thousand observations

GA (weeks) Centiles of MCA S/D to UA S/D ratio
1st 2.5th 5th 10th 90th 95th 97.5th 99th
13.0 0.29 0.33 0.38 0.44 1.12 1.27 1.41 1.60
13.5 0.30 0.35 0.40 0.46 1.18 1.33 1.48 1.68
14.0 0.32 0.37 0.42 0.48 1.23 1.40 1.56 1.76
14.5 0.34 0.39 0.44 0.51 1.29 1.46 1.63 1.84
15.0 0.36 0.41 0.47 0.53 1.35 1.53 1.70 1.92
15.5 0.37 0.43 0.49 0.56 1.41 1.59 1.77 2.00
16.0 0.39 0.45 0.51 0.58 1.46 1.66 1.84 2.08
16.5 0.41 0.47 0.53 0.61 1.52 1.72 1.91 2.16
17.0 0.42 0.49 0.55 0.63 1.58 1.78 1.98 2.23
17.5 0.44 0.51 0.57 0.66 1.63 1.84 2.05 2.31
18.0 0.46 0.53 0.59 0.68 1.69 1.91 2.11 2.38
18.5 0.47 0.54 0.61 0.70 1.74 1.97 2.18 2.46
19.0 0.49 0.56 0.63 0.73 1.79 2.02 2.25 2.53
19.5 0.50 0.58 0.65 0.75 1.84 2.08 2.31 2.60
20.0 0.52 0.60 0.67 0.77 1.89 2.14 2.37 2.67
20.5 0.53 0.61 0.69 0.79 1.94 2.19 2.43 2.74
21.0 0.55 0.63 0.71 0.81 1.99 2.24 2.49 2.80
21.5 0.56 0.64 0.72 0.83 2.03 2.29 2.54 2.86
22.0 0.57 0.66 0.74 0.85 2.08 2.34 2.60 2.93
22.5 0.58 0.67 0.75 0.86 2.12 2.39 2.65 2.98
23.0 0.59 0.68 0.77 0.88 2.16 2.44 2.70 3.04
23.5 0.60 0.69 0.78 0.89 2.20 2.48 2.75 3.09
24.0 0.61 0.71 0.79 0.91 2.23 2.52 2.79 3.15
24.5 0.62 0.72 0.81 0.92 2.27 2.56 2.84 3.20
25.0 0.63 0.73 0.82 0.94 2.30 2.60 2.88 3.24
25.5 0.64 0.73 0.83 0.95 2.33 2.63 2.92 3.29
26.0 0.65 0.74 0.84 0.96 2.36 2.66 2.96 3.33
26.5 0.65 0.75 0.84 0.97 2.39 2.70 2.99 3.37
27.0 0.66 0.76 0.85 0.98 2.41 2.72 3.02 3.41
27.5 0.66 0.76 0.86 0.98 2.44 2.75 3.05 3.44
28.0 0.67 0.77 0.86 0.99 2.46 2.78 3.08 3.47
28.5 0.67 0.77 0.87 1.00 2.48 2.80 3.11 3.50
29.0 0.67 0.77 0.87 1.00 2.50 2.82 3.13 3.53
29.5 0.67 0.78 0.88 1.01 2.51 2.84 3.15 3.56
30.0 0.68 0.78 0.88 1.01 2.53 2.86 3.17 3.58
30.5 0.68 0.78 0.88 1.01 2.54 2.87 3.19 3.60
31.0 0.68 0.78 0.88 1.02 2.55 2.89 3.21 3.62
31.5 0.68 0.78 0.89 1.02 2.56 2.90 3.22 3.64
32.0 0.68 0.78 0.89 1.02 2.57 2.91 3.24 3.66
32.5 0.68 0.78 0.88 1.02 2.58 2.92 3.25 3.67
33.0 0.68 0.78 0.88 1.02 2.59 2.93 3.26 3.69
33.5 0.67 0.78 0.88 1.02 2.59 2.94 3.27 3.70
34.0 0.67 0.78 0.88 1.01 2.60 2.94 3.28 3.71
34.5 0.67 0.78 0.88 1.01 2.60 2.95 3.28 3.72
35.0 0.67 0.77 0.88 1.01 2.60 2.95 3.29 3.73
35.5 0.66 0.77 0.87 1.01 2.60 2.96 3.30 3.73
36.0 0.66 0.77 0.87 1.00 2.60 2.96 3.30 3.74
36.5 0.66 0.76 0.87 1.00 2.61 2.96 3.30 3.75
37.0 0.65 0.76 0.86 1.00 2.61 2.96 3.31 3.75
37.5 0.65 0.75 0.86 0.99 2.60 2.96 3.31 3.76
38.0 0.64 0.75 0.85 0.99 2.60 2.96 3.31 3.76
38.5 0.64 0.75 0.85 0.98 2.60 2.96 3.31 3.76
39.0 0.64 0.74 0.84 0.98 2.60 2.96 3.31 3.77
39.5 0.63 0.74 0.84 0.97 2.60 2.96 3.32 3.77
40.0 0.63 0.73 0.83 0.97 2.60 2.96 3.32 3.78
  1. Reference ranges for MCA S/D ratio to UA S/D ratio based on 1284 observations show parabolic course which ranges from 0.29 to 3.33 with average 1.30 at 2nd trimester, and ranges from 0.65 to 3.78 with average 1.81 at 3rd trimester