20-Week Ultrasound (Anatomy Scan)

What is the 20-week ultrasound?

A 20-week ultrasound is a prenatal ultrasound that happens between 18 and 22 weeks of pregnancy. It’s a way to check on how the fetus is growing. It also looks for signs of congenital conditions or how an organ or body part looks.

The scan is one tool your pregnancy care provider uses to make sure the fetus and pregnancy are healthy. It also helps them catch any potential problems before birth. A 20-week ultrasound is also called an anatomy scan.

During your appointment, an ultrasound technician (sonographer) takes pictures and measurements of the fetal:

• Heart
• Brain, head neck and spine
• Kidneys and bladder
• Arms and legs
• Hands, fingers, feet and toes
• Lips, chin, nose, eyes and face
• Chest and lungs
• Stomach and intestines

They also:

• Record the fetal heart rate.
• Check the umbilical cord for blood flow and where it attaches to the placenta.
• Look at the position of the placenta.
• Measure the amount of amniotic fluid.
• Check your uterus, ovaries and cervix.

How does a 20-week ultrasound work?

Ultrasounds use sound waves to make pictures of the inside of your body. The technician will move a device called a transducer across your belly to get the images they need of the fetus. They’ll also take certain measurements and look at organs and body parts. Your provider uses the images to check on how the fetus is growing and look for possible health issues.

How do I prepare?

There isn’t much to do to prepare for your appointment. This will be one of your longer prenatal ultrasound appointments — around 45 minutes. This will likely be a separate appointment from your regular pregnancy care visit. Some providers suggest eating before. This may make the fetus move more, which can help the technician get all the measurements they need.

What can I expect?

Here is what you can expect:

1. You’ll lie down on the exam table.
2. The sonographer will ask you to slightly lower your pants and lift your shirt. They’ll put ultrasound gel on your belly.
3. They’ll move a transducer over different spots on your abdomen. They’ll take images and measurements of specific organs and parts by freezing the screen and clicking some buttons.
4. You may also see them draw lines to measure the length of the fetus’s limbs, head or belly.
5. If the fetus is in a position that makes it hard to take measurements, the technician might ask you to move around a little or take a drink of something sweet.
6. After your ultrasound technician has taken enough images and measurements to complete the scan, they’ll wipe the gel off your belly. Most ultrasound technicians will send you home with a few pictures as a keepsake.

Generally, your ultrasound technician will be quiet as they work. Don’t be alarmed if they don’t talk to you or share results as they go. Your obstetrician (or other healthcare provider) will go over the results with you either immediately after or at a follow-up appointment in the next few days.

Will it tell me the sex of the fetus?

Yes. Depending on the position the fetus is in, your technician may be able to see its genitals. If you don’t want to know the sex, speak up so they don’t accidentally spoil the surprise.

What are the risks and benefits of a 20-week ultrasound?

A 20-week ultrasound isn’t dangerous for you or the fetus. There aren’t harmful risks to the scan, but there’s a chance you could get false results.

The benefits outweigh any drawbacks, though. The ultrasound helps detect potentially life-altering health conditions. This can allow both you and your healthcare team to plan for any extra care your baby may need after birth. 

What do the results of a 20-week ultrasound tell you?

The test tells you and your pregnancy care team if the fetus is developing at a healthy rate for its age. It also checks for signs of congenital conditions (based on your chromosomes, or family history) and possible structural issues with major organs like its brain, heart and kidneys. Your provider also looks closely at the placenta’s position and checks to make sure there’s a safe amount of amniotic fluid.

The 20-week ultrasound doesn’t diagnose anything, though. If your pregnancy care provider is concerned about anything they see, they’ll order more tests.

When will I know the results?

Every facility does things a little differently, but in general, you’ll probably talk to your obstetrician right after the scan. The ultrasound tech will pass along the images and their findings, and then your provider will go over the results with you. The anatomy scan is usually a positive and reassuring experience. Most of the time, no major issues are found.

What conditions can it detect?

A 20-week ultrasound doesn’t find all congenital conditions. But the scan can help detect several serious conditions, like:

• Anencephaly
• Down syndrome, trisomy 18 and trisomy 13
• Cleft lip
• Spina bifida
• Congenital heart abnormalities
• Omphalocele
• Skeletal dysplasia
• Diaphragmatic hernia
• Renal agenesis

Will I need further tests or ultrasounds?

If your healthcare provider has concerns about anything in your 20-week scan, they may recommend:

• A follow-up appointment with a maternal fetal medicine specialist (a doctor who specializes in high-risk pregnancies)
• Amniocentesis
• Chorionic villus sampling
• Fetal echocardiogram

Speak with your healthcare provider early in your pregnancy to make sure you understand the types of noninvasive prenatal testing available to you. Some tests can happen before your 20-week ultrasound.

What questions should I ask at my appointment?

It’s normal to have a lot of questions at your 20-week ultrasound. Some of the questions you may want to ask include:

• Does everything look OK?
• How big is my baby?
• What are you looking at?
• What measurements are you taking?
• Will I know my results today?
• What happens if something doesn’t look right?
• Is this test safe?
• Is this the last ultrasound I’ll have during pregnancy?
• Can you tell if it’s a boy or a girl?