Biparietal diameter is the distance between the bilateral parietal bones of the fetus, and femoral length is the length of the femoral stem, which can usually be measured at 4-5 months of age. When the baby is 16 weeks pregnant, the average diameter of the biparietal diameter is 3.02±0.58cm, and the length of the femur is 2.1±0.51cm.At 17 weeks, the biparietal diameter is 3.97±0.44cm, and the length of the femur is 2.52±0.44cm.At 18 weeks, the biparietal diameter is 4.25±0.53cm, and the length of the femur is 2.71±0.46cm.At 19 weeks, the biparietal diameter is 4.52±0.53cm and the femur length was 3.03±0.5cm.At 20 weeks the biparietal diameter was 4.88±0.58cm and the femur length was 3.35±0.47cm.At 21 weeks the biparietal diameter was 5.22±0.42cm and the femur length was 3.64±0.4cm.At 22 weeks the biparietal diameter was 5.45±0.57cm and the femur length was 3.82±0.47cm.At 23 weeks the biparietal diameter was 5.45±0.57cm and the femur length was 3.82±0.47cm. 0.47cm. at 23 weeks the biparietal diameter was 5.8±0.44cm and the femur length was 4.21±0.41cm. at 24 weeks the biparietal diameter was 6.05±0.5cm and the femur length was 4.36±0.51cm. at 25 weeks gestation the biparietal diameter was 6.39±0.7cm and the femur length was 4.65±0.42cm. at 25 weeks gestation the biparietal diameter was 4.65±0.42cm. at 25 weeks gestation the biparietal diameter was 5.22±0.42cm and the femur length was 4.65±0.4cm.