Sonography is the most accurate diagnostic modality for the confirmation of a viable pregnancy during the first trimester. This occurs within the first 2 weeks after conception. Sonographic evidence of pregnancy does not exist at this stage. Abnormal gestational sac size is the most reliable indicator of abnormal outcome. Gestational sacs should be 5-mm MSD by the fifth gestational week.
Sonographic evidence is based upon demonstration of an abnormal embryo or gestational sac.
Sonographic diagnosis of embryonic demise usually is made on demonstration of an abnormal embryo. Sonographic evidence of an embryo lacking cardiac activity is the most specific indicator of embryonic demise. Caution is advised in the diagnosis of embryonic demise. Determination of whether the viewed structure is the embryo is critical, as no other morphologically recognizable structures, other than a heartbeat, exist at this stage of development. The embryo must be scanned thoroughly for evidence of a heartbeat.