X-ray
An X-ray film will show a marked gap between the pubic bones, normally there is a 4–5 mm gap but in pregnancy, hormonal influences cause relaxation of the connecting ligaments and the bones separate up to 9 mm. To demonstrate instability of the joint the patient is required to stand in the "flamingo" position, (standing with weight on one leg and the other bent). A vertical displacement of more than 1 cm is an indicator of symphysis pubis instability. A displacement of more than 2 cm usually indicates involvement of the sacroiliac joints.
Read more about this topic: Diastasis Symphysis Pubis