At seven weeks of pregnancy, the embryo is roughly the size of a blueberry, measuring about 10 millimeters (just under half an inch) from the top of the head to the bottom of the rump. It doesn’t look like a baby yet. The body is curled into a C-shape, the head is oversized compared to the rest, and a small tail-like structure is still visible. But this tiny form is changing fast, with facial features starting to emerge, a heart beating on its own, and limbs taking their earliest recognizable shape.
Facial Features Just Starting to Form
The face at seven weeks is more suggestion than structure. Small depressions where the nostrils will eventually open are now visible on the surface. The earliest layers of the retinas, the light-sensing tissue at the back of the eyes, are forming. Dark spots of pigment may mark where the eyes are developing, though they sit on the sides of the head rather than facing forward. Tiny folds of tissue indicate where the outer ears will grow. The mouth opening exists, but there are no lips yet in any recognizable sense.
The brain is the engine behind all of this. It’s growing rapidly and already dividing into distinct sections that will eventually control movement, thought, and basic body functions. Because the brain is developing so fast, the head makes up a large proportion of the embryo’s total size, giving it a top-heavy appearance.
Arms and Legs Are Taking Shape
The limb buds that appeared a week or two earlier have now grown into more defined structures. By seven weeks, the hands have taken on a polygon-like shape, almost like small paddles. Look closely (on a magnified image) and you can see moderate notching between emerging fingers, the tissue between them just starting to separate. The feet are rounded plates at this point, slightly behind the hands in development.
By the middle of the seventh week, the fingers separate more distinctly, and notching appears between the toes as well. The arms and legs are still very short relative to the body and bend at early joint points, but they are clearly limbs rather than simple bumps. The hands and feet can even come together at this stage.
A Beating Heart at 120 to 154 BPM
The heart has been beating since around week six, but by 6.3 to 7 weeks the normal heart rate has climbed to between 120 and 154 beats per minute. That’s roughly twice the resting heart rate of an adult. The heart is still forming its four chambers and is proportionally large for the embryo’s body. On an ultrasound with audio capability, this rapid flicker of heartbeat is often the first thing a parent notices.
The Tail Is Fading
One of the most visually striking features of an early embryo is a small tail extending from the bottom of the spine. All human embryos develop this temporary structure. By seven weeks, it is shrinking as the surrounding tissues absorb it. Within the next week or two, it will disappear entirely, eventually becoming the coccyx, or tailbone. Its presence at this stage is completely normal and one of the reasons the embryo still looks more like a tiny sea creature than a human baby.
What You’d See on an Ultrasound
If you have an ultrasound at seven weeks, you won’t see the level of detail described above with the naked eye. What you’ll typically see is a dark circular area (the gestational sac), a smaller bright ring inside it (the yolk sac, which provides nutrients to the embryo), and a small, oblong shape called the fetal pole. The fetal pole is the embryo itself. It often becomes visible on transvaginal ultrasound around six weeks, though in some pregnancies it doesn’t appear until as late as nine weeks.
At seven weeks, the fetal pole is large enough that the ultrasound technician can usually measure it and detect a heartbeat, which shows up as a rapid flickering motion on the screen. The embryo itself appears as a small bright spot rather than anything that looks human. You won’t be able to distinguish arms, legs, or facial features on a standard ultrasound image at this stage. Those details are real and developing, but they’re happening at a scale too small for the ultrasound to resolve clearly.
How Seven Weeks Compares to the Weeks Ahead
Seven weeks sits right in the middle of the embryonic period, which runs from conception through about week ten of pregnancy. During this window, all major organs and body systems are being established. The embryo is not yet called a fetus (that term applies starting around week ten or eleven) and is still in the most intensive phase of structural development.
Over the next two to three weeks, changes happen quickly. The fingers and toes will fully separate. The tail will vanish. The eyes will migrate closer to the front of the face. The embryo will nearly double in length. By week nine or ten, the overall shape starts looking recognizably human, with a rounder head, visible eyelids, and limbs that bend at elbows and knees. But at seven weeks, the embryo is still in its most alien-looking phase: a curled, translucent form with an oversized head, paddle hands, a shrinking tail, and a heart beating nearly three times a second.