Pregnancy Sonogram: Week by Week

A pregnancy sonogram, or ultrasound scan, is a safe way to see your baby develop, confirm your due date and check that things are progressing as expected. Most pregnancies include at least a couple of routine scans, and this guide walks through what each one looks for, week by week, in warm plain language. Every pregnancy is different, so treat this as a friendly map, not a set of rules, and always follow the advice of your own midwife or doctor.

What a pregnancy sonogram is

A pregnancy sonogram is an ultrasound scan that uses high frequency sound waves to create a moving image of your baby in the womb. A sonographer moves a probe over your abdomen, or in early pregnancy sometimes uses a slim internal probe, and the echoes that bounce back are turned into a picture on a screen. Because it uses sound rather than ionising radiation, ultrasound has been used to monitor pregnancy for decades with no evidence of harm when performed for medical reasons.

Scans do two jobs. They reassure, by showing a heartbeat and healthy growth, and they screen, by measuring the baby and checking anatomy so that care can be planned. If you want the general background to the technology, see our overview of how ultrasound works.

Early pregnancy: around 6 to 10 weeks

Not everyone has a scan this early, but you might if you have pain, bleeding, uncertain dates or a history that needs closer monitoring. A very early scan is often done as a transvaginal ultrasound, because the internal probe sits closer to the uterus and gives a clearer picture than scanning across the belly at this stage. Our guide to the transvaginal ultrasound explains what to expect from that.

Around six to seven weeks a scan may show the pregnancy sac and, often, a tiny flickering heartbeat, though timing varies and it is normal for it to be too early to see much. By eight to ten weeks the embryo is larger and easier to measure. If you are looking for detail on these milestones, our 8 week ultrasound guide covers this window. Try not to read too much into a single early scan, as an appointment a week or two later often gives a much clearer answer.

The dating scan: around 11 to 14 weeks

The first routine scan for many people is the dating scan, usually offered between about eleven and fourteen weeks. Its main job is to estimate your due date by measuring the length of the baby, which is more accurate than dating from your last period. It also checks how many babies you are carrying and confirms the heartbeat.

At this scan you may also be offered nuchal translucency screening, which measures the fluid at the back of the baby's neck and, combined with a blood test, helps estimate the chance of certain chromosomal conditions such as Down's syndrome. This is a screening test that gives a probability, not a diagnosis, and it is your choice whether to have it. Our 12 week ultrasound guide goes into this scan in more detail.

The anomaly scan: around 18 to 21 weeks

The second routine scan, often called the anomaly or mid pregnancy scan, is usually offered between eighteen and twenty one weeks. This is a detailed look at your baby's development. The sonographer examines the brain, heart, spine, face, kidneys, abdomen and limbs, checks the position of the placenta and measures growth and the amount of fluid around the baby.

Many parents also hope to learn the baby's sex at this scan. Whether this is offered depends on your clinic and country, and it is not always possible if the baby is lying awkwardly. The main purpose of the scan is health, not sex, so try to keep that in perspective. If something needs a closer look, you may be offered a follow up scan or referred to a specialist, which is a routine part of careful monitoring rather than a reason to panic.

Later pregnancy scans

After the anomaly scan, further scans are done only if there is a reason, such as checking the baby's growth, the position of the placenta, or your baby's position as the birth approaches. These growth scans measure the baby and estimate weight, though estimates carry a margin of error, so they guide care rather than give an exact figure.

Some parents also choose an elective 3D or 4D scan in the later weeks to see the baby's face. These bonding scans are popular, and are reasonable when done at a reputable clinic, but they are not a medical assessment and should not replace your routine care. Our guides to finding a 3D ultrasound clinic and a 4D ultrasound clinic explain how to choose one wisely.

How to prepare and what the scan feels like

A pregnancy sonogram is painless. For an abdominal scan you lie back, the sonographer applies gel to your belly and moves the probe over it. You may be asked to arrive with a full bladder for early scans. A transvaginal scan uses a slim probe placed gently inside the vagina, which can feel odd but should not be painful, and you can ask for it to stop at any time. Scans usually last around twenty to forty minutes depending on what is being checked and how the baby is lying.

• Wear a two piece outfit so your abdomen is easy to reach.
• Follow any instruction about a full or empty bladder.
• Bring your maternity notes and any previous scan reports.
• It is fine to bring a partner or supporter, though clinics may limit numbers.

Understanding your results and staying safe

During the scan the sonographer focuses on measuring and checking, and may not chat much while concentrating. Some results are shared straight away, while screening results that involve blood tests or specialist review come later. If the sonographer wants a second opinion, that is normal and not automatically a sign of a problem.

Ultrasound is very good but not perfect. A normal scan is reassuring but cannot guarantee that everything is or will remain fine, and screening tests give probabilities rather than certainties. That is exactly why your midwife and doctor look at the whole picture, your history, your blood tests and your scans together.

Frequently asked questions

How many scans will I have in pregnancy?

Many pregnancies include at least two routine scans, a dating scan around 11 to 14 weeks and an anomaly scan around 18 to 21 weeks. You may have more if there is a medical reason, such as bleeding, uncertain dates or a need to monitor growth. Your midwife or doctor will advise what is right for you.

Are pregnancy ultrasounds safe for my baby?

Yes, when done for medical reasons by trained staff. Ultrasound uses sound waves, not radiation, and has been used in pregnancy for decades with no evidence of harm. Health authorities do advise that scans be performed only when medically indicated rather than purely for souvenir images.

When can a scan tell the baby's sex?

The baby's sex can often be seen at the anomaly scan around 18 to 21 weeks, but it is not guaranteed. It depends on the baby's position and your clinic's policy, and some places do not offer this information. The scan's main purpose is checking your baby's health.

Why might I need a transvaginal scan early on?

In early pregnancy an internal, or transvaginal, scan often gives a clearer view than scanning across the belly, because the probe sits closer to the uterus. It can help confirm the pregnancy, check the heartbeat and date the pregnancy accurately. It should not be painful, and you can ask to pause at any time.

What is a 3D or 4D bonding scan?

A 3D scan builds a surface image of the baby's face, and a 4D scan shows that image moving in real time. These elective scans are for bonding and keepsakes rather than diagnosis. They can be lovely, but they do not replace your routine medical scans, so keep attending your standard appointments.