Prenatal pattern emergence in early human facial development.

This report addresses the emergence of proportional patterns in the early development of the human face. Fifty-nine human embryos and fetuses (7 through 26 weeks fertilization age) constituted a "normal" study sample. Midfacial cephalometric analyses were done on projected histologic sections cut frontally through the maxillary deciduous first molar tooth crowns. The midface was divided into three cephalometric zones. Data show that while each zone increases in absolute width, least change is seen in the central facial zone, with greatest change seen in the lateral-most facial zone. This pattern of proportional stability of the central facial zone becomes evident at 9 weeks gestation, at which time the changing embryonic optical axes have converged toward the midline to within several degrees of their position at birth. These data show that the central portion of the postnatal facial T-zone has a clearly recognizable prenatal antecedent as early as the ninth week in fetal life.