At 8 weeks of pregnancy, an embryo measures roughly 16 to 22 millimeters from head to bottom, which is about the size of a kidney bean. That’s just under an inch long, and it weighs approximately 1 gram. Despite being tiny enough to sit on your fingertip, the embryo is in the middle of a rapid building phase, with all major organs and body systems actively forming.
How Size Is Measured at 8 Weeks
Doctors measure early embryos using what’s called crown-rump length, the distance from the top of the head to the base of the torso. Legs aren’t included because they’re still curled tightly against the body at this stage. At the start of week 8, the typical crown-rump length is about 16 mm. By the end of the week, it reaches around 22 mm. That’s a growth of roughly 1 mm per day, which is remarkable given how small the embryo still is.
This measurement is one of the most reliable ways to confirm how far along a pregnancy is. If you have an early ultrasound, your provider will likely use the crown-rump length to assign or adjust your due date, since it’s more precise than counting from your last period.
What the Embryo Looks Like at 8 Weeks
By week 8, the embryo is starting to look distinctly human, though it still has some unusual features. The hands and feet have formed but are webbed, with fingers and toes not yet separated. Eyes are becoming visible as dark spots on the sides of the head, and the ears are beginning to take shape. The head is still disproportionately large compared to the rest of the body, accounting for nearly half the total length. A small tail that was present in earlier weeks is almost gone.
Arm and leg buds first appeared around week 6, and by now they’ve grown into recognizable limbs with joints starting to develop. The embryo can even make tiny, spontaneous movements at this point, though you won’t feel them for many more weeks.
What’s Developing Inside
The most significant changes at 8 weeks are happening internally. All of the major organs and body systems are actively developing. The heart has been beating since around week 5 and is now pumping at a rapid pace. The brain is growing quickly, forming the structures that will eventually control movement, sensation, and thought. The digestive system, lungs, and kidneys are all taking shape, even though none of them will need to function on their own for months.
The umbilical cord is fully developed by this point, delivering oxygen and nutrients from your bloodstream to the embryo. This cord is the embryo’s lifeline for the remainder of the pregnancy.
What You’d See on an Ultrasound
At 8 weeks, a transvaginal ultrasound can typically pick up the embryo, its heartbeat, and the gestational sac surrounding it. The embryo will appear as a small, bright shape inside the darker fluid-filled sac. You’ll likely be able to see the flickering of the heartbeat on screen, and your provider may let you hear it.
Seeing a heartbeat at 8 weeks is a reassuring milestone. Research on women with a history of pregnancy loss found that a visible heartbeat at 8 weeks was associated with a 98% chance of the pregnancy continuing. That number climbs to over 99% by week 10.
Your Body at This Stage
Even though the embryo is barely the size of a small bean, your uterus has already grown to roughly the size of a tennis ball by week 8. Before pregnancy, it’s closer to the size of a small pear. This expansion is why many people start noticing bloating, increased urination, or a feeling of fullness in the lower abdomen, even though a visible bump is still weeks away.
Embryo Versus Fetus
At 8 weeks, your baby is still technically called an embryo. The shift to “fetus” happens at the end of week 10 of pregnancy. The distinction isn’t arbitrary. During the embryonic period (weeks 3 through 10), the basic architecture of every organ system is being laid down. Once that foundational work is complete, the fetal period begins, and the focus shifts to growth and maturation of structures that already exist. So at 8 weeks, you’re in the final stretch of the most intensive phase of organ formation.