The double sac sign of early intrauterine pregnancy: use in exclusion of ectopic pregnancy.

Pelvic sonograms from 61 consecutive patients with suspected ectopic pregnancy and an additional 17 proved ectopic pregnancy cases were reviewed retrospectively. Special attention was given to the appearance of the uterus and intrauterine fluid collections in the absence of a fetal pole. Criteria for the exclusion of an ectopic pregnancy were established, based on a specific morphologic appearance of the decidua seen in early normal intrauterine pregnancy. A "double sac" appearance of two concentric echogenic rims was consistently identified early in normal intrauterine pregnancies before the appearance of a fetal pole, and served as a good morphologic discriminator for the decidual cast of ectopic pregnancy. We think the double sac appearance is a helpful indicator for differentiating an ectopic pregnancy from an early normal intrauterine pregnancy.