ABSTRACT
Since the introduction of high-frequency transvaginal transducers, sonographic visualization of embryos and fetuses in early stages has progressed remarkably and the field of sonoembryology has become well established. Furthermore, recent advances in three- and four-dimensional (3D/4D) ultrasound combined with the transvaginal approach have produced more objective and accurate information on early embyonic and fetal development and the natural history of fetal abnormalities.
