At 7 weeks pregnant, your baby is about the size of a blueberry. In actual measurements, that’s roughly 8 to 13 millimeters long, or about half an inch from the top of the head to the bottom of the torso. Despite being tiny enough to sit on your fingertip, a surprising amount of development is already underway.
What “Blueberry-Sized” Actually Looks Like
When pregnancy sources say “blueberry,” they’re measuring crown-to-rump length, which is the distance from the top of the embryo’s head to its bottom. Legs aren’t included because they’re still just small buds at this point and can’t be straightened out for measurement. This is the standard way embryos are measured on ultrasound throughout the first trimester.
The head makes up a large proportion of that half-inch. At 7 weeks the embryo’s head is oversized compared to the rest of the body, which is normal. Think of a tadpole shape that’s just starting to look less curved and more structured. By next week, your baby will have roughly doubled in size to about the length of a kidney bean, so growth is happening fast.
What’s Developing at 7 Weeks
Size is only part of the picture. Week 7 is when soft cartilage starts being replaced by actual bone tissue. This is the beginning of a skeleton, though it will take months before bones fully harden. Genitals are also beginning to form internally, though it’s far too early to determine sex on an ultrasound.
The arm and leg buds that appeared around week 6 are continuing to grow. Hands and feet are forming flat, paddle-like plates that will eventually separate into fingers and toes. Facial features are also taking shape: the tissue that will form the nostrils and upper lip is fusing together, and dark spots where the eyes will be are becoming more defined.
The brain is developing rapidly, generating new nerve cells at an extraordinary pace. The neural tube, which will become the brain and spinal cord, closed during week 5, and now the brain is beginning to divide into distinct sections. This is why folic acid intake is so important in the early weeks of pregnancy.
The Heartbeat at 7 Weeks
One of the most notable milestones at this stage is the heartbeat. The tiny heart tube started pulsing around week 5 at roughly 110 beats per minute. By week 7, that rate is often faster, sometimes reaching 150 beats per minute or more. For comparison, a resting adult heart beats about 60 to 100 times per minute. The embryo’s heart needs to beat this quickly because it’s powering rapid cell growth and development with a circulatory system that’s still incredibly small.
What You’ll See on a 7-Week Ultrasound
If you have an ultrasound at 7 weeks, it will likely be a transvaginal scan rather than one done on your belly, since the embryo is still so small that an abdominal ultrasound may not pick up enough detail. Here’s what your provider will look for:
- Gestational sac: The fluid-filled space surrounding the embryo. This is one of the earliest visible signs of pregnancy and confirms that the pregnancy is located in the uterus.
- Yolk sac: A small white ring or bubble inside the gestational sac. It provides nutrients and oxygen to the embryo until the placenta takes over. It’s often the first structure visible, even before the embryo itself.
- Heartbeat: If the embryo is in a good position, you’ll see a tiny blinking or pulsing on the screen. Most providers will briefly let you hear it as well. Seeing a heartbeat at 7 weeks is a reassuring sign.
Don’t panic if a 7-week ultrasound doesn’t show everything clearly. Dating can be off by a week or more, especially if your cycle is irregular. What looks like a 7-week pregnancy might actually be closer to 6 weeks, where the heartbeat and embryo are harder to detect. Your provider will typically schedule a follow-up scan if the initial one is inconclusive.
Changes in Your Body
While your baby is blueberry-sized, your uterus has already grown to about the size of a lemon. Before pregnancy, it’s closer to a small pear. You won’t have a visible bump yet since the uterus is still tucked behind the pelvic bone, but you may notice your waistband feeling tighter or some bloating. This uterine growth, along with rising hormone levels, is what’s behind many of the first-trimester symptoms like nausea, breast tenderness, and fatigue that tend to peak over the next few weeks.