The 20-Week Anatomy Scan: What It Checks and How to Prepare

The gel is cold, the lights are down, and for a long stretch nobody says very much. On the screen your baby yawns, throws an arm across their face and settles again, and you find yourself watching somebody you have not met yet do something completely ordinary.

This is one of the most detailed looks at your baby you will get before birth, and it is also a working appointment: the person holding the probe is moving through a list you cannot see. Here is what is on that list, what an ultrasound can and cannot show you, and what it means if they ask you to come back, so the quiet stretches make sense while you are sitting in them.

What the anatomy scan actually is

The 20-week scan is a detailed ultrasound that examines how your baby is developing. Unlike an early dating scan, which mostly confirms how far along you are, this scan is a careful head-to-toe review of your baby’s anatomy. The sonographer measures growth and looks closely at the major organs and structures to check that everything is forming as expected. It is one part of routine care during the second trimester, and for many parents it is the first long, calm look at the tiny person they have been growing.

It is worth knowing what this scan can and cannot do. It is a screening tool, which means it is designed to spot many common differences but cannot catch everything. A reassuring scan is genuinely good news, and at the same time, no scan can guarantee a baby will have no health conditions at all. Holding both of those truths gently is the healthiest way to approach the day.

When it happens

This scan is usually offered between 18 and 22 weeks of pregnancy. That window exists for a reason: by this point your baby is large enough that the organs can be seen clearly, but still small enough to view in detail. If you are not sure exactly where you are in your pregnancy, our pregnancy week by week guide can help you keep track. Your clinic will give you a specific appointment time, and it is fine to ask why if it falls outside that range.

What the sonographer checks, and why

During the scan, the sonographer works through your baby’s body in a methodical order. This is not a quick glance. Each structure is viewed on its own, sometimes from several angles, which is why the appointment can feel long and quiet, and why the person doing it may not talk much while they work. Here is what is on their checklist.

What they check	Why it matters
Head and brain	Confirms the skull and brain structures are forming and measures growth.
Face, including the lip	Helps identify differences such as a cleft lip that may benefit from early planning.
Spine	Checks that the bones and skin covering the spine are intact along its length.
Heart and its chambers	Reviews the four chambers and major vessels to see that blood flow looks as expected.
Stomach	Confirms the stomach is present and in the right place.
Kidneys and bladder	Checks the kidneys are developing and the bladder is filling and emptying.
Abdominal wall	Confirms the wall has closed properly around the organs.
Arms, legs, hands, and feet	Counts and measures the limbs and looks at the long bones.
Placenta position	Notes where the placenta is sitting, which can affect later care.
Umbilical cord	Checks the cord and the vessels running through it.
Amniotic fluid level	Confirms there is a healthy amount of fluid around your baby.

If your baby is curled up or facing away, the sonographer may ask you to move, take a short walk, or have a snack to encourage a wiggle. This is completely normal and does not mean anything is wrong. Sometimes a second appointment is needed simply because the baby would not cooperate for a clear view.

Finding out the sex

By this stage, the sonographer can usually see your baby’s sex, so this is the scan where many parents choose to find out. It is entirely up to you. If you want to know, say so at the start. If you would rather be surprised, tell them clearly so they can keep that part of the screen and conversation private. Keep in mind that the view is not always perfect, so there is a small chance the answer is uncertain. If learning your baby’s sex is on your mind, our guide on finding out your baby’s sex walks through the options and timing in more detail.

How to prepare

Preparing for the anatomy scan is refreshingly simple, but a few things help the appointment go smoothly:

Follow your clinic’s bladder instructions. Some clinics ask you to arrive with a comfortable but not overly full bladder, since this can improve the view. Others have no requirement at all. Always go by what your clinic tells you rather than general advice.
Wear something comfortable. Two-piece outfits make it easy to expose your belly without undressing fully.
Allow plenty of time. The scan itself often takes around 20 to 45 minutes, and it can run longer if your baby is in an awkward position or the clinic is busy.
Think about who comes with you. Many clinics welcome a partner or support person, though some limit numbers or ask that children do not attend. Check ahead so there are no surprises.
Bring your questions. It is easy to forget what you wanted to ask once you are watching the screen, so jot a note on your phone beforehand.

If something needs a closer look

This is the part that worries people most, so here it is plainly. Most anatomy scans are reassuring. Sometimes, though, the sonographer notices something they want to examine more closely, or a particular view is hard to get. When that happens, you may be offered a follow-up scan or a referral to a specialist. Try to remember that a flag usually means more information is needed, not that something is definitely wrong.

Many findings turn out to be minor or resolve on their own, and even when a real difference is found, knowing early gives your care team time to plan and support you well. If you are asked back, it is fair to ask what they saw, what the next step is, and when you will have answers. You do not have to sit with uncertainty in silence.

It also helps to remember that some things simply cannot be seen on a scan. Ultrasound is powerful, but it has limits. A clear scan is genuinely good news, and it is not a promise that nothing will ever come up. Take the reassurance it offers without expecting it to answer every possible question.

Most people walk out of this appointment lighter than they walked in. If you leave with a follow-up appointment instead, that is a date in the calendar, and usually a request for more information.

Medical disclaimer: This article is for general educational purposes only and is not medical advice. It does not replace care from a doctor, midwife, or other qualified professional. Always speak with a healthcare provider about your scans and any pregnancy concern. If you think you may be experiencing a medical emergency, contact your local emergency services right away.