OSSIFICATION SEQUENCE OF OCCIPITAL BONE AND VERTEBRAE IN HUMAN FETUSES

The aim of this radiographic study of human fetuses was to examine the pattern and sequence of ossification in the occipital bone and the sp inal vertebrae. Together with previous studies of ossification of the human fetal basal cranium, this study can serve as a reference for nor malcy in future studies of fetuses with neural tube defects and associ ated pathological development of the axial skeleton. Thirty-nine norma l fetuses aborted between 9 and 14 weeks of gestation were examined. B ased on the appearance of ossification centers in the bones under stud y, the fetuses could be grouped in four well-defined developmental sta ges, which were named occipito-spinal stages I-IV (OS I-IV). The OS st age was closely related to gestational age, crown-rump length, foot le ngth, and degree of ossification in the hands and feet.