By week
What a scan shows, week by week
Real scans change a lot over a pregnancy. Knowing roughly what each stage looks like helps you read a scan you've been shown, and pick a prop that fits the story you're telling.
Weeks here are counted the way clinics count them, from the first day of the last period, so "8 weeks pregnant" is about 6 weeks after conception. Sizes are rough averages; real babies vary, and only a clinician can read a real scan.
| Week | What's on the screen | Rough size | Usual scan |
|---|---|---|---|
| 5 to 6 | A small dark circle (the gestational sac), often with a tiny bright ring inside (the yolk sac). A flicker of heartbeat may show from about 6 weeks. | A few millimeters | Early scan, often internal (transvaginal) |
| 7 to 8 | A curved, bean-shaped embryo next to the yolk sac. The heartbeat is usually visible. No face, no limbs you could point to. | About 1 to 1.6 cm, raspberry-ish | Early or viability scan |
| 10 to 12 | Now it looks like a baby: a big head, a body, arm and leg buds, sometimes moving. The classic "first scan" picture. | About 4 to 6 cm crown to rump at 12 weeks | Dating scan, often with a nuchal measurement (11 to 14 weeks) |
| 18 to 22 | A full profile, the spine, the four chambers of the heart, hands and feet. The sonographer usually checks the body in sections, so you get several close-ups instead of one whole-baby picture. | About 25 cm head to heel at 20 weeks | Anatomy scan, where many parents learn the sex |
| 26 to 32 | Too big to fit on the screen at once. Prints from this stage are usually close-ups of the face. | About 35 to 42 cm head to heel | Growth scans if needed; elective 3D and 4D scans are often done around now |
Why 3D scans look so different
A standard scan is a 2D slice, grey and grainy, like looking at a loaf of bread one slice at a time. A 3D scan stacks many slices into a sepia-toned surface picture of the face. 4D is the same thing moving. Most routine NHS and insurance-covered scans are 2D; 3D and 4D are usually paid extras at private studios.
What this means if you're reading a scan
If the stated week and the picture don't match, something's off: a profile with a nose and lips can't be from 7 weeks, and a tiny bean can't be from 20. More on this on our real or novelty page.
What it means if you're choosing a prop
For an early announcement ("we just found out"), a 6 to 8 week scan matches the story. For "we're past the first trimester", go for 12 weeks; it's also the stage most people picture when they hear "first scan". A 20-week scan suits a gender reveal, since that's when many parents find out.
Sources for the sizes and timings: the NHS pages on the 12-week and 20-week scans, and ACOG's patient guides on ultrasound in pregnancy. They're worth reading if you're pregnant; we are not a medical site.