Ultrasound in Pregnancy

A prenatal ultrasound (or sonogram) is a test during pregnancy that checks on fetal growth and development. An obstetrician, nurse midwife or ultrasound technician (sonographer) performs ultrasounds for different reasons. Sometimes, it’s to check growth and development. Other times, it’s because your provider noticed a potential concern.

During an ultrasound, sound waves are sent through your abdomen or vagina by a device called a transducer. The sound waves bounce off structures inside your body and the fetus. Then, the sound waves transform into images that your provider can see on a screen.

Pregnancy ultrasounds are safe and don’t have known harmful side effects. Still, they’re typically done only when it’s medically necessary. Your provider will let you know when to expect them based on your health history.

Why do you need an ultrasound during pregnancy?

An ultrasound is one of the main ways your healthcare team monitors your pregnancy.

Reasons why your provider may perform a prenatal ultrasound are to:

• Confirm your pregnancy and due date
• Check for early pregnancy complications
• Monitor high-risk pregnancies
• Determine the gestational age (how far along the pregnancy is)
• Check the fetus’s growth, movement and heart rate
• Look for multiple fetuses
• Examine pelvic organs, like your uterus, ovaries and cervix
• Measure how much amniotic fluid you have
• Check the location of the placenta
• See fetal position in your uterus
• Detect problems with fetal organs, muscles or bones

Your provider also uses ultrasound to guide the needle during amniocentesis or CVS (chorionic villus sampling).

It’s also part of a biophysical profile (BPP). This is a test that combines ultrasound with a nonstress test.

How many are typically done during pregnancy?

One or two. But the number and timing vary depending on your pregnancy care provider and if you have any health conditions. If your pregnancy is high-risk or if your provider suspects you or the fetus has a health condition, they may suggest more.

When is the first ultrasound typically done during pregnancy?

The timing of your first ultrasound varies depending on your provider. Some people have an early ultrasound around seven to eight weeks of pregnancy. Providers perform an early ultrasound through your vagina (transvaginal ultrasound). Early ultrasounds do the following:

• Confirm pregnancy (by detecting a heartbeat)
• Check for multiples
• Measure the size of the fetus
• Help confirm gestational age and due date

Some providers do your first ultrasound closer to 12 weeks of pregnancy.

20-week ultrasound (anatomy scan)

You can expect an ultrasound around 18 to 20 weeks in pregnancy. This is known as the anatomy ultrasound or 20-week ultrasound. If your pregnancy is healthy and there aren’t any concerns, it could be your last one. If your provider sees something they want to check more closely, they may recommend more ultrasounds.

How do prenatal ultrasounds work?

The two main types of pregnancy ultrasound are transvaginal and abdominal. Both use the same technology to create images. For a transvaginal ultrasound, your provider places a wand-like device inside your vagina. For an abdominal ultrasound, they move a device over the skin of your belly. Providers use abdominal ultrasounds after about 12 weeks of pregnancy.

There’s no special preparation for an ultrasound. Some providers may ask that you come with a full bladder. You can bring a support person, but bringing children is discouraged since the exam requires complete focus.

You may be asked to change into a hospital gown, but this isn’t usually required for abdominal ultrasounds. If your provider is performing a transvaginal ultrasound in your first trimester, you’ll put on a hospital gown or undress from the waist down.

Your provider may recommend other types of ultrasounds. Examples of additional ultrasounds are:

• Doppler ultrasound: This type of ultrasound checks how the fetus’s blood flows through its blood vessels. Most Doppler ultrasounds occur later in pregnancy.
• Fetal echocardiogram: This type of ultrasound looks at the fetus’s heart size, shape and how well it’s working. Your provider may use it if they suspect a congenital heart condition, if you have had another child who has a heart condition or if you have certain health conditions.

What should I expect during a prenatal ultrasound?

You’ll lie on a padded examining table during the test. Your sonographer applies a small amount of gel to the skin of your belly. The gel doesn’t harm your skin or stain your clothes, but it may feel cold. This gel helps transmit sound waves more efficiently.

Next, the sonographer places a transducer on the skin of your belly. The transducer sends sound waves into your body. The sound waves that reflect back create pictures on a screen. You may see the sonographer making lines on the screen or clicking a button to “freeze” certain angles.

If you have a transvaginal ultrasound, the transducer is inside your vagina and not on your belly. Everything else is the same.

What should I expect after the ultrasound?

After an abdominal ultrasound, your sonographer will wipe the gel off your belly. They may give you pictures to take home. An obstetrician will review the images and go over the results with you — often at a follow-up scheduled the same day.

In most cases, the sonographer won’t discuss your ultrasound results. If your obstetrician does the ultrasound, they may explain what they see as they go along.

What results do you get on a pregnancy ultrasound?

The results can be either normal or abnormal. A normal result means your pregnancy care provider didn’t find any problems. An abnormal result means your provider noticed something irregular. If it’s abnormal, your provider will order more ultrasounds or tests.

Sometimes, the ultrasound is incomplete. The fetus’s position or movement can make it hard to see everything clearly. If this happens, you may need another ultrasound.

What are reasons you need more ultrasounds?

Some of the reasons you may need more ultrasounds include:

• There are issues with your ovaries, uterus, cervix or other pelvic organs.
• The fetus is measuring small for its age.
• There are problems with the placenta.
• You’re pregnant with twins, triplets or more (multiples).
• The fetus is breech.
• You have too much or too little amniotic fluid.
• You have a condition like gestational diabetes or preeclampsia.
• The fetus has a congenital disorder.