The spectrum of first-trimester ultrasound findings.

A wide spectrum of sonographic findings can be seen in the first trimester of pregnancy. One must have an appreciation of embryology to recognize normal and abnormal early pregnancy development. In this article we emphasize discriminatory criteria for identification of normal structures, as well as ultrasound findings in threatened abortion, failing pregnancy, multiple gestations, ectopic pregnancy, and trophoblastic disease. Sonoembryology, the identification of embryonic anatomy, is discussed, as are examples of early identification of anomalies.