These anomalies, which can include multiple levels, are the result of and broadly classified as a failure of formation or a failure of segmentation (or both) during vertebral development (Figure 2). Because
these spinal deformities are present in utero, they are often first identified on fetal ultrasound (12). Organ systems that
develop at the same gestational time (fifth to sixth week)
may also demonstrate abnormalities in up to 60% of cases