Fetal spine morphology and maturation during the second trimester. Sonographic evaluation.

We reviewed high-resolution real-time sonographic images (especially selected for a lack of technical artifacts) of the fetal spine of 46 normal fetuses between 18-27 menstrual weeks of development. The degree of visible posterior neural arch ossification was graded and compared with the gestational age. Recognizable early ossification of the laminae was seen in the cervical region of all fetuses studied. Similar ossification followed sequentially in the thoracic, lumbar, and sacral regions; however, sonographically recognizable ossification of the laminae in the lumbar spine was delayed until 22-24 weeks and in the sacral spine until 25 weeks or more. Awareness of these features will help to prevent false-positive diagnoses of dysraphism and, conversely, hopefully augment our ability to detect such lesions.