Ultrasound at 4 Weeks: What to Expect & What's Visible

In most pregnancies, a gestational sac can be seen on an ultrasound at four weeks. It appears as a small, circular structure containing the embryo. The embryo itself may not be visible at this stage, as it is still very small. However, in some cases, the earliest sign of pregnancy—the embryonic pole—may be visible on an ultrasound at four weeks. The embryonic pole is the tiny structure that will eventually develop into the fetus.