At 7 weeks of pregnancy, the embryo is about the size of a blueberry, measuring roughly 1 centimeter from head to tail. It has a distinctly curved, C-shaped body with a large head that makes up nearly half its total length, tiny limb buds starting to take shape, and a small tail that is still visible but beginning to shrink away.
Overall Shape and Size
The embryo at this stage looks nothing like a baby yet. Its body curves forward into a tight C-shape, with the oversized head tucked toward what will become the chest. Medical providers measure the embryo from the top of the head (the crown) to the bottom (the rump), and at 7 weeks that crown-to-rump length is about 1 centimeter. That small, curved structure sits inside a fluid-filled gestational sac, drawing nutrients from a tiny pouch called the yolk sac that’s visible right alongside it.
One of the most noticeable features is a small tail-like structure at the bottom of the embryo. This tail develops around weeks five and six and is completely normal. It’s in the process of disappearing and will be gone by the eighth week of pregnancy as the surrounding tissues absorb it.
The Face Is Just Starting to Form
The face at 7 weeks is still extremely rudimentary. Where the nose will eventually be, small depressions that will give rise to nostrils are just becoming visible on the surface. The very earliest layers of the retinas, the light-sensing tissue at the back of the eyes, are forming, though the eyes themselves are still dark spots positioned on the sides of the head rather than the front. There are no eyelids yet. Slight thickenings on either side of the head mark where the ears will eventually develop, but they don’t resemble ears in any recognizable way.
The mouth area is also taking early shape as tissue folds begin to merge. At this point, the entire face occupies a tiny fraction of the head, and most of what you’d see under magnification is smooth, translucent skin stretched over rapidly growing brain tissue underneath.
Arms, Legs, and the Beginnings of Fingers
The limbs at 7 weeks look like small paddle-shaped buds extending from the body. The arm buds are slightly more developed than the leg buds since upper limbs consistently form a few days ahead of lower ones. At the end of each arm bud, a flattened hand plate is forming. Within these plates, faint ridges called digit rays mark where individual fingers will eventually separate. That separation happens through a process where the tissue between the rays naturally breaks down over the coming weeks, carving out distinct fingers and toes.
The legs are a step behind. They appear as shorter, rounder buds without clearly defined foot plates yet. Neither the arms nor legs bend at this stage; there are no functional elbows, wrists, or knees.
Brain Development Is Accelerating
The reason the head looks so disproportionately large is that the brain is growing faster than any other organ. By 7 weeks, the neural tube (the precursor to the brain and spinal cord) has closed, and the front end has ballooned into three distinct sections: the forebrain, midbrain, and hindbrain. The forebrain will later split further into the structures responsible for thinking, sensory processing, and hormone regulation. The hindbrain will become the area that controls balance and basic body functions like breathing.
This rapid brain growth is why the head accounts for such a large proportion of the embryo’s body. It will remain oversized relative to the rest of the body for several more weeks.
The Heart Is Already Beating
The heart started beating around week six, and by 7 weeks it has divided into its right and left chambers. The heart rate at this stage typically falls between 120 and 154 beats per minute, significantly faster than an adult heart. A rate below 120 bpm at 6.3 to 7 weeks can signal a less favorable outcome, which is why heart rate is one of the first things checked on an early ultrasound.
The heart is visible as a flickering motion on ultrasound, often the most dramatic thing to see at a 7-week scan. The circulatory system is basic but functional, with blood already moving through a simple loop of vessels. The liver has begun producing blood cells, taking over a job that was previously handled by the yolk sac.
What You’d See on an Ultrasound
If you have an ultrasound at 7 weeks, you won’t see anything that looks like a baby. What appears on the screen is a dark, round gestational sac with a small bright structure inside it: the fetal pole. The fetal pole is the earliest visible form of the embryo, and it appears as a tiny, curved white shape nestled next to the circular yolk sac. Your provider will measure the fetal pole from crown to rump to confirm the gestational age.
Most 7-week ultrasounds are transvaginal rather than abdominal because the embryo is still too small to visualize clearly through the abdomen. On the screen, the gestational sac looks like a dark circle roughly 2 to 3 centimeters across, and the embryo inside it is a small echogenic (bright) sliver. The flickering heartbeat is usually the easiest landmark to spot. Facial features, limb details, and organ structures are far too small to distinguish on a standard ultrasound at this stage.
What’s Forming Inside
Internally, the major organs are all in some stage of early development, even though none are fully functional yet. The liver is the largest internal organ at this point and is already producing blood cells. The kidneys are forming in a preliminary version that will be replaced by more mature kidney tissue later. The intestines are beginning to develop but are so long relative to the tiny abdominal cavity that a loop of them actually extends into the umbilical cord temporarily.
The lungs exist as small buds branching off the tissue that will become the windpipe. They won’t need to function until birth, but the branching process that creates the airways starts now. Tiny clusters of cells are differentiating into what will become the pancreas, thyroid, and other glands, though none are producing hormones yet. The skeletal system is entirely cartilage at this stage, with no true bone anywhere in the body. Ossification, the gradual replacement of cartilage with bone, won’t begin for several more weeks.