An 8 week scan is often the first time you see your baby. At this stage an ultrasound can usually show the heartbeat, the yolk sac and an embryo measuring roughly 15–22 mm from head to bottom. It can also confirm that the pregnancy is in the womb, how many babies there are and your estimated due date. With a high-resolution probe, we can even capture a real 3D image of an embryo at just 8 weeks.
This guide explains what you’ll see at an 8 week scan, how big the embryo is, what 3D imaging can (and can’t) show this early, and what happens if the scan doesn’t show what you expected.
At a glance: embryo about 15–22 mm long (about the size of a raspberry) · heartbeat typically 158–186 bpm · yolk sac about 4–5.5 mm across · single or multiple pregnancy confirmed · estimated due date.
What will I see at an 8 week scan?
At 8 weeks, Dr Ushakov and our fetal medicine team will look for:
- The heartbeat: seen on screen as a fast, regular flicker, and measured.
- The gestational sac: the fluid-filled sac in which the pregnancy develops. Seeing it inside the womb confirms the pregnancy is in the right place.
- The yolk sac: a small round structure beside the embryo that nourishes it in the earliest weeks. At 8 weeks it typically measures about 4–5.5 mm across.
- The embryo: its crown–rump length (CRL, the length from the top of the head to the bottom) is measured to date the pregnancy.
- How many babies: whether this is a single or a multiple pregnancy.
- The future placenta: the placenta is developing and attaching itself to the wall of the womb.
From these measurements we give you an estimated due date. That gives you plenty of time to pack the hospital bag and plan your babymoon.
How big is the embryo at 8 weeks?
Most pregnancy apps compare your baby with a fruit, a vegetable, an animal or even baked goods. Rarely do you see how your baby would actually fit into the palm of your hand. The model below shows the real size of an embryo at 8 weeks.
The NHS describes a baby at 8 weeks as around 16 mm long, about the size of a raspberry, and notes that it will roughly double in size by the following week. Standard dating charts show how quickly this changes within a single week:
| Crown–rump length | Approximate stage of pregnancy |
|---|---|
| 15 mm | 7 weeks 6 days |
| 16 mm | 8 weeks 1 day |
| 18 mm | 8 weeks 3 days |
| 20 mm | 8 weeks 4 days |
| 22 mm | 8 weeks 6 days |
| 23 mm | 9 weeks 0 days |
Because the embryo grows by around a millimetre a day at this stage, even a few days’ difference in when you ovulated shows up clearly on the scan. That’s why dates from a scan can differ from dates based on your last period. At 8 weeks the arms are getting longer and are bigger than the legs, and the head has started to uncurl a little.
Your baby’s heartbeat at 8 weeks
At 8 weeks the heart beats far faster than yours. In a large reference study, the typical range was 158–186 beats per minute (bpm), with an average of 174 bpm. The rate peaks at around 9 weeks and then slowly settles over the rest of pregnancy. Our guide to fetal and maternal heart rates shows the typical heart rate week by week.
Can you see a baby in 3D at 8 weeks?
Yes, with the right equipment. We always like to test the capabilities of the latest ultrasound technology, and this is a real 3D image of an embryo at just 8 weeks.
A 3D image at this stage shows the overall shape of your baby: the head, the body and the developing arms and legs. It’s a wonderful first picture, but the baby’s structures are still too small to examine in detail with ultrasound at 8 weeks. The essential checks (heartbeat, location, size and number of babies) are made with standard 2D imaging, and 3D is an addition to them rather than a replacement.
A detailed look at your baby’s anatomy becomes possible later. Our 10 week scan is the earliest structural anomaly scan, and the early fetal scan (12–16 weeks) checks your baby in much more detail. For the classic 3D/4D “bonding” images of your baby’s face, see our 3D and 4D scans.
Is 8 weeks too early for NIPT?
Yes. Non-invasive prenatal testing (NIPT) screens for certain chromosomal conditions by analysing DNA from the placenta that circulates in your blood. Depending on the test (for example the Harmony test), NIPT can be taken from 9 or 10 weeks, so 8 weeks is too early for a reliable result. We always perform NIPT alongside a scan.
Will I need an internal scan at 8 weeks?
At 8 weeks the pregnancy is still small and sits low in the pelvis. An internal (transvaginal) scan, using a slim probe placed gently in the vagina, often gives the clearest view. NICE guidance for early pregnancy units recommends a transvaginal scan to check the location of the pregnancy and look for the heartbeat. An abdominal scan is sometimes enough, and it is always your choice. If you would prefer not to have an internal scan, tell us and we will explain what an abdominal scan can and can’t show at this stage.
What if the scan doesn’t show what I expected?
Sometimes the embryo looks smaller than your dates suggest, or the heartbeat can’t be seen yet. Most often this is because the pregnancy is simply earlier than you thought. NICE guidance sets out cautious rules before any diagnosis is made. If the embryo measures under 7 mm with no visible heartbeat, a repeat scan should be done at least 7 days later. If it measures 7 mm or more, a second opinion and/or a repeat scan at least 7 days later is advised. We will talk you through what we have seen and what the next step is.
If you have bleeding or tummy pain, the NHS advises getting advice promptly from your maternity unit or local early pregnancy unit (for pregnancies under 20 weeks), or from NHS 111. Call 999 if the bleeding is heavy, or you have severe pain, shoulder-tip pain or feel faint. For a same-day private scan, see our early pregnancy bleeding scan.
NHS or private 8 week scan?
On the NHS, your first routine scan is the dating scan, which the NHS says usually takes place between 8 and 14 weeks. It is free, and you’ll be offered it through your midwife. If you have pain or bleeding before then, your maternity unit or early pregnancy unit can assess you, which may include a scan.
Many parents choose an earlier private scan for reassurance or because they want to see their baby sooner. Our viability scan is designed for 6–9 weeks: it confirms the heartbeat, dates the pregnancy, checks for a single or multiple pregnancy, and examines the gestational sac, yolk sac and early placenta. You can book a viability scan (£140) at either of our London clinics, or call us on 020 3687 2939 for more information. See all of our early pregnancy scans to compare options, or read what else is happening this week in week 8 of pregnancy.
Key takeaways
- An 8 week scan usually shows the heartbeat, the gestational and yolk sacs, and an embryo of about 15–22 mm.
- The heart typically beats at around 158–186 bpm at this stage.
- 3D imaging at 8 weeks gives a real first picture, but detailed anatomy checks come later, from 10 weeks.
- It’s too early for NIPT. Depending on the test, it can be taken from 9 or 10 weeks.
- If the scan looks earlier than expected, a repeat scan at least 7 days later is often the next step.
This information is intended for general educational purposes only and does not constitute medical advice. Please consult a qualified healthcare professional for guidance specific to your individual circumstances. If you have concerns about your pregnancy or baby’s wellbeing, contact your midwife, GP, or maternity unit promptly.
