The main trajectories measured outside the pelvis are the inter-iliac crest diameter, the inter-iliac spine diameter, the outer sacral pubic diameter and the transverse exit diameter. 1. Inter-iliac crest diameter: It is the distance between the outer edges of the iliac crest on both sides measured. The normal value is 25-28cm; 2. Inter-iliac spine diameter: It is the distance between the outer edges of the anterior superior iliac spine on both sides measured. The normal value is 23 to 26cm; 3. Sacro-pubic outer diameter: is the distance from the midpoint of the superior border of the pubic symphysis to the depression under the spinous process of the fifth lumbar vertebra. Normal value is 18-28cm; 4, exit transverse diameter: measure the distance between the sciatic tuberosity diameter. The normal value is 8.5 to 9.5cm.