8 to 12 Weeks Pregnancy Scan — What Changes Week by Week
The four weeks in which an embryo becomes recognisably a baby. What each week shows, how an 8-week scan differs from a 12-week one, and which week answers your question.
More changes between eight and twelve weeks than in any comparable stretch of pregnancy. At eight weeks you are looking at a curved embryo under two centimetres long; by twelve it has a profile, a spine, moving limbs and measurable proportions. That difference is why people ask which week to scan — and the answer depends entirely on what you want the scan to tell you. This guide compares the weeks directly, then covers each in turn.
What each week shows
| Week | Typical CRL | What is visible | What the scan can answer |
|---|---|---|---|
| 8 weeks | About 16–22mm | Distinct embryo, limb buds, early movement, clear heartbeat | Viability, dating, number of pregnancies |
| 9 weeks | About 23–30mm | Head and body distinguishable, limbs moving | Viability and dating, with better detail |
| 10 weeks | About 31–40mm | Recognisable human shape, fingers and toes forming | Dating, reassurance, early anatomy overview |
| 11 weeks | About 41–52mm | Profile visible, spine, active movement | Dating; nuchal translucency window opens |
| 12 weeks | About 55–65mm | Full profile, limbs, major structures forming | Accurate dating and the NHS combined screening window |
Measurements are typical guides — a few millimetres either side is ordinary variation, and dating is set by measurement rather than by calendar. The fetal heart rate peaks around weeks nine to ten at roughly 170 beats per minute, then gradually settles as pregnancy progresses; our guide to fetal heart rate by week gives the ranges.
8 week scan versus 12 week scan
These two answer genuinely different questions, which is why one does not replace the other.
An 8-week scan answers “is this pregnancy viable and where is it?” — confirming a heartbeat, confirming the pregnancy is inside the uterus, establishing dates, and identifying twins. It is the reassurance scan, and it arrives early enough to matter if you have been anxious or have had a previous loss. What it cannot do is assess anatomy: at eight weeks the structures simply are not formed enough to examine.
A 12-week scan answers “how is this pregnancy developing?” — the most accurate dating of the whole pregnancy, a first look at major structures, and the window in which nuchal translucency is measured. In the UK this is the NHS dating scan, offered to everyone.
One thing worth being straight about: we do not provide NHS 12-week combined screening. That programme — the nuchal translucency measurement combined with blood tests to assess chromosomal risk — belongs to the NHS pathway, and your NHS scan is the right place to have it. Our guides to the nuchal translucency scan and the NIPT test explain how that screening works so you can go into it informed.
The 8 week scan in detail
Eight weeks is the most-scanned week in this window, and with reason: it is the earliest point at which a scan reliably gives a clear answer in a single visit. The embryo measures roughly 16–22mm — about the size of a raspberry — with a heartbeat that should be plainly visible, limb buds appearing, and often small movements.
What a normal 8-week scan looks like: a gestational sac containing a clearly formed embryo, a yolk sac still present alongside it, cardiac activity, and measurements matching your dates within a few days. What prompts further assessment: no visible heartbeat in an embryo measuring 7mm or more, a sac of 25mm or more with no embryo, or measurements substantially behind expectation. None of those is automatically conclusive — UK practice confirms findings with a second opinion or a repeat scan before anything is decided, as our guide to no heartbeat at 8 weeks explains.
Scanning at eight weeks is usually still transvaginal for best detail, though an abdominal approach sometimes gives an adequate view by now depending on build and uterine position. For the full week-eight picture, see our dedicated 8 week pregnancy scan guide; week nine has its own guide too.
How the picture fills in
Nine weeks brings proportion: the head becomes distinguishable from the body, limbs lengthen and move visibly, and the embryo — now formally a fetus — measures around 23–30mm. The yolk sac begins to recede as the placenta takes over.
Ten weeks is when most people first describe the image as looking like a baby. At roughly 31–40mm, fingers and toes are forming, the profile is emerging, and movement is often unmistakable.
Eleven weeks opens the nuchal translucency window, which runs from about 11 weeks to 13 weeks and 6 days — measured on the NHS pathway as part of combined screening. The fetus measures around 41–52mm with a clear spine and profile.
Twelve weeks gives the most accurate dating of the entire pregnancy. After this point, dating by measurement becomes progressively less precise, which is why the 12-week scan sets the due date that stands for the rest of the pregnancy.
Which week should you scan?
If you want reassurance as early as it is reliable, eight weeks. If you want a clearer picture with the same reassurance, nine or ten. If you want accurate dating and early anatomy, wait for twelve — and note that the NHS provides that scan, so a private one is generally only worth it if you want it sooner or in addition.
If you have symptoms — bleeding, pain — do not schedule around a table. Contact an Early Pregnancy Assessment Unit, your GP or midwife now; many EPAUs accept self-referral.
Severe or one-sided tummy pain, pain at the tip of your shoulder, heavy bleeding, or feeling faint or dizzy — go to A&E or call 999.
Your questions answered
What is the difference between an 8 week and a 12 week ultrasound?
What does a normal 8 week ultrasound look like?
How big is the baby at 8, 10 and 12 weeks?
Is 8 weeks or 9 weeks better for a scan?
Do you offer the NHS 12 week combined screening?
Is the scan internal or abdominal at this stage?
When is the due date finally set?
The week-by-week guides
The week in full — measurements, what is visible, and what a normal scan shows.
Read the guide →
9 Weeks9 Week Pregnancy ScanProportion, movement, and a recognisable shape emerging.
Read the guide →
7 Weeks7 Week UltrasoundThe week before — day-by-day measurements and what to expect.
Read the guide →
Scanning between 8 and 12 weeks
Viability, dating and reassurance by HCPC-registered sonographers, explained on screen as it happens, with a written report usually within two hours for your GP or midwife.
Kensington, London W8 4ED
3 mins from Notting Hill Gate
Measurements are typical reference guides; individual variation is normal and dating should be interpreted by the clinician reporting your scan. Diagnostic thresholds follow NICE guideline NG126; NHS scanning and screening pathways per NHS guidance on pregnancy ultrasound scans. This article is general information, not individual medical advice — urgent symptoms need urgent assessment.
Written and clinically reviewed by the HCPC-registered sonographers who perform this scan at IUS London — a CQC-registered diagnostic ultrasound clinic (Provider ID 1-2775844974). Your own findings are explained to you at the scan and set out in your report.
Author: Yianni Kiromitis, Senior Sonographer, HCPC RA38415
Medically reviewed: 1 August 2026
