At 7 weeks pregnant, your baby is about the size of a blueberry, measuring roughly half an inch (10 mm) from the top of the head to the bottom of the torso. That measurement, called crown-rump length, is the standard way embryos are measured this early since the legs are too small and curled to include. Your baby has doubled in size since last week, and while half an inch sounds tiny, a remarkable amount of development is packed into that small frame.
What Half an Inch Looks Like
Ten millimeters is about the width of a pencil eraser. At this stage the embryo is still fairly featureless to the naked eye, but under magnification or on ultrasound, distinct body parts are starting to emerge. The head makes up a large proportion of the total length because the brain is growing rapidly. Between weeks 6 and 7, the brain’s main chambers actually double in size, driving that oversized head shape you’d see on an early scan.
Limbs, Face, and Eyes Taking Shape
Tiny arm and leg buds have been present for about a week, but at 7 weeks they’re lengthening noticeably. The arm buds stay a day or two ahead of the legs throughout this period. The ends of these buds are flattening into paddle-like shapes that will eventually become hands and feet, and nerves have already begun growing into the limbs.
The face is changing too. External ears are appearing, and the eyes are starting to shift toward the front of the head as the skull grows. Eye pigment cells begin forming this week, though your baby’s final eye color won’t actually settle until around 10 months after birth. Muscle cells are also developing around the jaw and face, laying the groundwork for future facial expressions.
A Heartbeat You Can See
One of the most dramatic developments at 7 weeks is the heart. It’s been beating since around week 5 or 6, but by now it has a normal rate of roughly 120 to 154 beats per minute. That’s significantly faster than an adult heart. A rate above 155 bpm at this stage is considered unusually rapid and something your provider would monitor. On a transvaginal ultrasound, the heartbeat often shows up as a visible flicker, which is one of the most reassuring signs at an early appointment.
Organs Already Under Construction
Even at blueberry size, internal organs are forming. The liver is one of the most active organs this week. Bile ducts are reorganizing and establishing connections between the liver and the developing gut, and the earliest biliary structures are taking shape in the surrounding tissue. The digestive tract is beginning to differentiate into its separate sections, though none of these organs are functional yet in the way they’ll be at birth. They’re essentially being built and wired before they’re switched on.
What You’d See on an Ultrasound
If you have an ultrasound around 7 weeks, it will almost certainly be transvaginal rather than abdominal, since the embryo is still too small to pick up clearly through the belly. Here’s what typically shows up on the screen:
- Gestational sac: A dark, fluid-filled space inside the uterus. This is the largest and most obvious structure.
- Yolk sac: A small circular structure inside the gestational sac, usually 3 to 5 millimeters across. It provides nutrients to the embryo before the placenta takes over.
- Fetal pole: The early form of the embryo itself, visible as a small bright shape next to the yolk sac.
- Heartbeat flicker: A rapid pulsing visible on the fetal pole, confirming cardiac activity.
At this stage, you won’t be able to make out arms, legs, or facial features on the screen. The embryo appears as a small oblong shape. Your provider will measure the crown-rump length to confirm gestational age, which is one of the most accurate dating methods available in early pregnancy.
How Size Changes Week to Week
Growth in the first trimester is exponential. At 6 weeks, your baby was only about a quarter of an inch. By 7 weeks it has doubled to half an inch. By 8 weeks it will be closer to the size of a raspberry, around 0.6 inches. This rapid doubling pace is why early ultrasound measurements can pin down your due date so precisely: even a few days of growth creates a measurable difference at this scale.
If your measurements come back slightly smaller or larger than expected, that’s common. Embryos don’t all grow at exactly the same rate day to day, and a difference of a millimeter or two can shift the estimated age by several days. Your provider will look at the overall picture, including heartbeat and sac size, rather than crown-rump length alone.