Ultrasonographic and radiologic visualization of the developing embryonic skeleton.

We investigated the development of the skeleton in the embryonic and early fetal period both with ultrasonography and radiology. Eight normal embryos/fetuses were studied weekly with real-time transvaginal sonography between 8 and 16 weeks of gestation to establish the ultrasonographic characteristics of normal ossification. Additionally, ossification was studied in radiographs obtained from five embryos/fetuses between 9 and 14 weeks of gestation. Ossification centers, visualized as increased echogenicity of the bone, were recognized with ultrasonography from 9 weeks onwards. The appearance of primary ossification centers as observed by transvaginal ultrasonography was at the same gestational age or at most 1 week later than when obtained with radiography or whole-specimen staining techniques. Transvaginal ultrasonography enables early visualization of ossification centers in the embryo and fetus. Detailed knowledge of the development of ossification of the skeleton may contribute to early prenatal diagnosis of skeletal dysplasias.