Early intrauterine pregnancy or decidual cast: an anatomic--sonographic approach

In order to differentiate an early intrauterine gestation from an ectopic pregnancy with decidual cast, demonstration of the uterine cavity as a structure distinct from the gestational sac is suggested. Anatomically, normal implantation occurs separately from the endometrial canal, whereas decidual casts form within the canal. Using real-time sonography, physician observers were able to demonstrate two separate structures in 79 per cent of normal pregnancies of eight weeks' gestation or less when a special effort was made; routine longitudinal and transverse static and real-time scans were less helpful.