The fetal pole is the first ultrasound-visible evidence of the developing embryo within the gestational sac. It appears as a small, echogenic thickening on the edge of the yolk sac, typically becoming visible on transvaginal ultrasound at approximately 5.5 to 6 weeks of gestational age. The fetal pole is measured as the crown-rump length, which is the most accurate method for dating a pregnancy in the first trimester. Cardiac activity is usually detectable in the fetal pole once it reaches a certain size, generally around 7 millimeters. The presence of a fetal pole with cardiac activity confirms a viable intrauterine pregnancy, while the absence of a heartbeat in a fetal pole of sufficient size suggests a nonviable pregnancy.
Sonography Term