表1 正常妊娠胎头双顶径值（cm） 孕周 均值原则差 孕周 均值原则差 11 2.080.577 26 6.310.773 12 2.350.525 27 6.670.820 13 2.580.515 28 7.090.403 14 3.030.757 29 7.230.682 15 3.450.580 30 7.390.802 16 3.790.358 31 7.930.636 17 4.100.820 32 7.940.580 18 4.280.406 33 8.130.367 19 4.260.630 34 8.300.628 20 4.680.711 35 8.470.614 21 4.790.681 36 8.520.515 22 5.150.568 37 8.710.566 23 5.471.000 38 8.880.354 24 5.800.704 39 8.910.536 25 5.811.380 40 9.090.429 表2 头围（HC）及腹围（AC）旳正常均值（cm） 孕周 HC AC 孕周 HC AC 12 7.0 5.6 27 25.2 22.9 13 8.9 6.9 28 26.2 24.0 14 9.8 8.1 29 27.1 25.0 15 11.1 9.3 30 28.0 26.0 16 12.4 10.5 31 28.9 27.0 17 13.7 11.7 32 29.7 28.0 18 15.0 12.9 33 30.4 29.0 19 16.3 14.1 34 31.2 30.0 20 17.5 15.2 35 31.8 30.9 21 18.7 16.4 36 32.5 31.8 22 19.9 17.5 37 33.0 32.7 23 21.0 18.6 38 33.6 33.6 24 22.1 19.7 39 34.1 34.5 25 23.2 20.8 40 34.5 35.4 26 24.2 21.9 表3 股骨长度正常值（cm）孕周 股骨长度 孕周 股骨长度 孕周 股骨长度 12 0.8 22 3.9 32 6.3 13 1.1 23 4.2 33 6.5 14 1.5 24 4.4 34 6.6 15 1.8 25 4.7 35 6.8 16 2.1 26 4.9 36 7.0 17 2.4 27 5.2 37 7.2 18 2.7 28 5.4 38 7.3 19 3.0 29 5.6 39 7.5 20 3.3 30 5.8 40 7.6 21 3.6 31 6.1