Sacral agenesis (also considered as part of the caudal regression syndrome) is a rare and severe sacral developmental abnormality.
In normal pregnancy, the incidence is between 0.005 and 0.1%. However, in fetuses with diabetic mothers, the incidence rises to 0.2%. Of those with the condition, 16-20% have diabetic mothers.
Sacral agenesis can be categorised into four types 1:
- type I: unilateral agenesis localised to sacrum or coccyx
- type II: partial agenesis with bilateral defects; the iliac bone articulates with S1, but the distal sacral elements fail to develop
- type III: total sacral agenesis; iliac bones articulate with the lowest lumbar element
- type IV: total sacral agenesis; iliac bones fuse posteriorly