This is a sonogram demonstrating CRL of an 8 weeks fetus. The arrow in the field points to which of the following?

The above USG image shows Anaechoic (black) gestational sac with an embryo and yolk sac (arrow). The yolk sac is seen as a small well-defined anaechoic structure in side the Gestational sac.Presence of yolk sac or fetal pole within the gestation sac confirms pregnancy. Double decidua sign of the gestational sac is due to the interface between the decidua and the chorion, which appears as two distinct layers of the wall of the gestation sac.