At 8 weeks of pregnancy, your baby is about 15 to 16 millimeters long, roughly the size of a kidney bean. It has a recognizable head and body, tiny forming limbs, and facial features that are just starting to emerge. This is also a milestone week: it’s the final week your developing baby is classified as an embryo. Starting at 9 weeks after fertilization, it officially becomes a fetus.
Overall Size and Shape
The crown-to-rump length, measured from the top of the head to the bottom of the torso, is about 15 mm. That’s slightly more than half an inch. At this stage, the head is disproportionately large compared to the rest of the body, making up nearly half the total length. The body has a slight C-shaped curve, and the small tail-like structure that was present in earlier weeks is being absorbed back into the body, eventually becoming part of the tailbone.
Facial Features Taking Shape
The face is changing quickly at 8 weeks. The eyes become noticeable, though they sit wide apart on the sides of the head and won’t move to a more forward-facing position for several more weeks. Eyelids are beginning to form but won’t fully cover the eyes for a while yet. The upper lip and nose have formed, giving the face a more recognizable profile. Small swellings are appearing where the outer ears will eventually take their shell-like shape, though right now they’re positioned low on the head.
Arms, Legs, Fingers, and Toes
Tiny hands and feet are forming this week, with webbed fingers and toes starting to take shape. The limbs have grown from simple buds into structures with visible segments, though the webbing between the digits won’t fully disappear for another week or two. On ultrasound, you can sometimes see the beginning outlines of arms and legs extending from the body, though they’re still very short relative to the head and torso.
First Movements
Even though you won’t feel anything for months, your baby is already moving. Research using ultrasound has documented that movements become visible as early as 8 to 9 weeks. These include general whole-body movements, startles, hiccups, stretches, isolated arm and leg movements, and even hand-to-face contact. These movements are involuntary, driven by the rapidly developing nervous system rather than any conscious intent. The brain’s nerve cells are branching and connecting at a remarkable pace during this period.
What’s Happening Inside
The heart has been beating for a few weeks already, but by week 8 it’s becoming more structurally complex, dividing into its four chambers. On ultrasound, the heartbeat shows up as a visible flicker. Internally, the foundations for nearly every major organ system are in place. The lungs, liver, kidneys, and digestive tract are all in early stages of development, though none are functional yet. The intestines are growing so rapidly that they temporarily extend into the umbilical cord because there isn’t enough room in the abdomen.
External sex organs have not yet differentiated. That process begins around 9 weeks of gestation, so at 8 weeks there’s no visible difference between male and female embryos. It will be several more weeks before sex can be determined on ultrasound.
What You See on an 8-Week Ultrasound
If you have an ultrasound at 8 weeks, several structures are visible. The gestational sac appears as a dark, fluid-filled space. Inside it, you’ll see the yolk sac, a small white circle typically less than 6 mm across, which provides early nutrition to the embryo. The embryo itself shows a distinct head and body with limb buds starting to extend outward. The heartbeat appears as a rapid flicker, and most providers will measure it to confirm it falls within a healthy range.
The placenta is also visible at this point, appearing as a grainy or textured area attached to the uterine wall. It’s still in early development but is already beginning to take over the job of supplying nutrients. Don’t expect a baby-shaped image on the screen at this stage. The embryo looks more like a small, rounded form with a large head and tiny protruding limbs. The detail is limited, and much of what’s described above is happening at a scale too small to see clearly without magnification.
How 8 Weeks Compares to Nearby Weeks
Development moves fast in the first trimester. At 6 weeks, the embryo was about the size of a lentil with only the earliest limb buds. By 8 weeks, it has recognizable arms and legs, a forming face, and the beginnings of fingers and toes. By 10 weeks, the webbing between the fingers will be gone, the tail will have fully disappeared, and the embryo (now officially a fetus) will have started to look distinctly human in proportion. Week 8 sits right at that transition point, where the basic body plan is established and the fine details are rapidly filling in.