At 7 weeks of pregnancy, the developing baby is roughly the size of a blueberry, measuring between 8 and 16 millimeters from head to bottom depending on the exact day of the week. Medically, it’s still called an embryo at this stage (that term applies through 8 weeks after fertilization, per the American College of Obstetricians and Gynecologists). Despite being tiny, the 7-week embryo has a recognizable shape and is undergoing rapid, dramatic changes.
Size and Shape on Ultrasound
On a transvaginal ultrasound, the embryo appears as a small curved structure called the fetal pole, sitting inside a fluid-filled gestational sac. Next to it is a round pouch called the yolk sac, which supplies nutrients at this early stage. The fetal pole is sometimes described as bean-shaped: one end is the head (the crown), and the other tapers into a small tail-like structure (the rump). Your provider measures the distance between these two points, known as crown-rump length, to confirm how far along the pregnancy is.
At 7 weeks 0 days, the crown-rump length averages about 8 to 9 millimeters. By 7 weeks 6 days, it’s closer to 15 or 16 millimeters. That’s roughly the width of a dime to the width of a penny. Growth at this stage is fast enough that even a day or two makes a visible difference on ultrasound.
The Head and Face
The head is disproportionately large compared to the rest of the body, making up a significant portion of the embryo’s total length. This is normal and reflects how rapidly the brain is growing. The head and face contours are just starting to emerge during week 7, though the features are still very basic.
Small depressions mark where the nostrils are forming. Eyelids are beginning to take shape, though they won’t open for months. The outer ears are developing as small folds of tissue on the sides of the head. Lip formation, which started around week 4, is wrapping up. The retina of the eye also begins to develop this week. At this point, none of these features look recognizably human to the naked eye, but the building blocks for a distinct face are actively being laid down.
Limbs and Digits
The arms and legs have progressed from simple buds into more defined structures. By week 7, the upper limbs have a visible hand plate at the end, with a developing wrist region between the hand and arm. On the hand plate, faint lines called digital rays have appeared. These are the earliest precursors to individual fingers, though the digits haven’t separated yet. The lower limbs are slightly behind: a foot plate is forming, but it’s less developed than the hands.
This pattern, where the arms develop ahead of the legs, continues throughout the first trimester. The limbs are still paddle-like and tiny, but they’re growing quickly and will look much more recognizable within the next two weeks.
The Tail Is Shrinking
One of the more surprising features of a 7-week embryo is that it still has a visible tail. All human embryos develop a tail early on, and at its longest, it’s relatively prominent. During weeks 7 and 8, the tail undergoes rapid regression. The body breaks down the extra tissue through a process of programmed cell death, and by the end of the embryonic period, the tail is completely gone. At 7 weeks, you’d still see a small remnant, which is one reason the embryo retains that curved, comma-like shape.
Heart Activity
The heart has been beating since around week 6, and by week 7 it’s pumping with a detectable rhythm on ultrasound. The normal heart rate at 6.3 to 7.0 weeks is at least 120 beats per minute, which is roughly twice the resting heart rate of an adult. Seeing this flicker of cardiac activity on an early ultrasound is one of the most common reasons people search for what the embryo looks like at this stage. The heart itself is still very simple, with its four chambers not yet fully separated, but it’s already circulating blood through a basic network of vessels that extends into the limb buds.
What’s Happening Inside
Most of the embryo’s major organs are in the process of forming during week 7, even though they aren’t functional yet. The brain is growing quickly and has already divided into its primary regions. The liver, which is proportionally large at this stage, has begun producing blood cells. The kidneys are in an early developmental form.
One less obvious change is happening in the gut. Around 7 weeks, the rapidly growing intestines start to herniate, or push outward, into the base of the umbilical cord. This sounds alarming but is completely normal. The embryo’s abdominal cavity is simply too small to contain the intestines at this point. They’ll migrate back inside the abdomen later in the first trimester, typically by around week 12.
What You Won’t See Yet
At 7 weeks, there are no visible sex organs, so it’s far too early to determine sex on ultrasound. The embryo doesn’t have recognizable fingers or toes yet, just the ridged plates that will become them. Bones haven’t formed; the skeleton is made of soft cartilage. The skin is paper-thin and translucent, which means on high-resolution imaging the underlying structures are partially visible through it.
If you’re looking at an ultrasound image, the embryo will appear as a small bright shape against the dark fluid of the gestational sac. It won’t look like a baby yet. The features that make a fetus recognizably human, such as a defined nose, separated fingers, and proportional body, develop over the next several weeks. At 7 weeks, the embryo is in one of its most intense periods of structural change, transforming daily in ways that are invisible to anyone not looking through an ultrasound transducer.