Caudal regression syndrome is a rare congenital malformation with varying degrees of early gestational developmental failure. It is also known as sacral agenesis or caudal dysplasia. The cause of this malformation is thought to be defects in neuralization around the 28^th day of the gestational period. Although maternal uncontrolled diabetes, genetic predisposition and vascular hypoperfusion are the possible risk factors, actual pathogenesis is unclear. CRS is generally diagnosed at prenatal assessment, but also a varying number of newborns with some degree of anomaly may be presented. In our case, we diagnosed a caudal regression syndrome fetus early in the second trimester. Determination of the pathology early in the gestational age gives parents a chance for termination of pregnancy. Although diabetes mellitus is the major risk factor for CRS, as in our case, sporadic presentations may occur. So clinicians should consider CRS when CRL is shorter than expected and incomplete vertebral ossification is observed both in gray scala and 3D imaging ultrasonography.

Keywords: Caudal regression syndrome, sirenomelia, diabetes mellitus, vertebral anomaly, 3D ultrasonography