Anatomy Scan Preparation: What to Expect at Your 20-Week Ultrasound

The 20-week anatomy scan — also called the mid-pregnancy ultrasound or anomaly scan — is one of the most anticipated appointments of pregnancy. Around 18–22 weeks, your provider will order a detailed ultrasound to check how your baby is growing and developing. For many families, it is also the moment they learn whether they are having a boy or a girl. This guide walks you through what the scan looks for, how to prepare, and the questions worth asking so you can walk in feeling informed and at ease.

What is the anatomy scan?

The anatomy scan is a detailed, non-invasive ultrasound performed in the second trimester, typically between 18 and 22 weeks. It is more thorough than earlier ultrasounds: the sonographer takes a careful, systematic look at your baby's organs, bones, growth, and the surrounding environment — the placenta, amniotic fluid, and umbilical cord. The scan usually takes 30–45 minutes, sometimes longer if your baby is not in a cooperative position.

It is important to know that the anatomy scan is a screening exam, not a diagnostic one. It looks for signs of concern, but it cannot catch every condition, and a normal scan does not guarantee a perfectly healthy baby. Likewise, an unexpected finding does not always mean something is wrong — many findings are minor or resolve on their own. Your provider will help you interpret the results in context.

What the scan looks for

The sonographer will examine many structures and measurements. Here is what they are typically assessing:

Baby's growth and development

• Head and brain — skull shape, brain structures, and fluid-filled spaces (ventricles)
• Face — profile, nasal bone, and checking for cleft lip
• Spine — alignment and closure of the spinal column
• Heart — four chambers, heart rate, and the major vessels
• Abdomen — stomach, kidneys, bladder, and the abdominal wall
• Limbs — arms, legs, hands, and feet, with bone length measurements

The environment around your baby

• Placenta position — checking for a low-lying or placenta previa, which can affect birth plans
• Amniotic fluid volume — too much or too little can signal certain conditions
• Umbilical cord — blood flow and the number of vessels (typically three: two arteries and one vein)
• Cervix — sometimes measured to assess length

Measurements and dating

• Biometry — head circumference, abdominal circumference, and femur length to estimate growth and confirm your due date
• Estimated fetal weight — calculated from the measurements

How to prepare for your anatomy scan

A little preparation can help the scan go smoothly and make the experience more meaningful.

Before the appointment

• Check your provider's instructions on fluids. Some practices ask you to drink water beforehand so you arrive with a full bladder, which helps lift the uterus and improve the image. Others no longer require this — follow your specific clinic's guidance.
• Eat normally. A snack beforehand can encourage your baby to move, which helps the sonographer get better views. Some people find a small amount of juice or something sweet about 30 minutes before helps.
• Wear a two-piece outfit. You will need to expose your belly, so a top you can easily lift is more comfortable than a dress.
• Bring your partner or support person. Most practices allow one support person in the ultrasound room. Check your clinic's current policy.
• Prepare your questions in advance. Write them down so you do not forget in the moment.
• Decide about finding out sex. If you want to know (or do not want to know) whether you are having a boy or girl, tell the sonographer before the scan begins.

Mindset and expectations

• Be patient. The sonographer may be quiet and focused while taking measurements — this is normal and does not mean something is wrong.
• Know that baby's position matters. If your baby is facing your spine or curled up, the sonographer may ask you to roll onto your side, walk around, or drink something sweet to encourage movement. Sometimes a follow-up scan is needed.
• Understand the limits. Some structures are harder to see clearly, and not all conditions are detectable on ultrasound. A clear scan is reassuring, but it is not a guarantee.

Questions to ask at your anatomy scan

The sonographer is focused on capturing images and may not be able to discuss findings in depth — they often leave interpretation to your provider. Still, it is helpful to ask what you can, and then follow up with your midwife or OB. Consider these questions:

About the scan itself

• How is my baby's growth measuring compared to my due date?
• Were you able to see all the structures you needed to, or will we need a follow-up scan?
• How is the placenta positioned, and are there any concerns about its location?
• How is the amniotic fluid level?
• How many vessels are in the umbilical cord?

About findings and next steps

• Did you notice anything that we should follow up on?
• What does this finding mean, and how common is it?
• What are the next steps — another scan, a referral, or additional testing?
• What would change in my care based on these results?
• When will I hear from my provider with the full report?

About your birth plans

• Does anything about this scan affect my birth location or birth plan?
• Are there any reasons to adjust my activity level or care schedule?

Understanding your results

After the scan, your provider will review the images and report with you. Some things to keep in mind:

• "Soft markers" are minor findings that can be associated with certain conditions but are often normal variations. Your provider will explain what they mean for your situation and whether any follow-up is recommended.
• A follow-up scan is common. If your baby was not in a good position, or if a structure needs another look, a repeat scan a few weeks later is routine — not necessarily a sign of a problem.
• Additional testing is your choice. If a finding raises questions, your provider may offer further screening or diagnostic options. You always have the right to ask about the benefits, risks, and what the results would (or would not) change.

After the scan

Give yourself space to process what you learn. A clear scan is a beautiful milestone — take it in. If something unexpected came up, give yourself time and ask all the questions you need. Your midwife or provider is there to walk through every detail with you, and you are always welcome to bring a partner or support person to follow-up conversations.

Educational information only — Individual care should be discussed with your maternity care provider.