(a and b) Transvaginal ultrasonography revealed membranous fetal vessels passing across the cervical internal os considered to be related to a low-lying bilobate placenta. Therefore, a diagnosis of vasa previa was made. The red arrow indicates a small space between the placental vessels and the internal os. (c and d) Images of the placenta obtained by transvaginal ultrasonography. The red arrows indicate the vessels thought to be vasa previa.
