When can the gestational sac be seen?

The gestational sac is the structure that appears the earliest. It is an image with no echoes (dark) and surrounded by a refringent halo (white), located inside the uterus (specifically, in the endometrium). The fledgling gestational sac can usually be seen in week 5 of pregnancy, but it is preferable to wait one more week to be sure of the diagnosis.