What it tests for
and how it’s performed

According to the March of Dimes, ultrasound (also referred to as sonogram) uses sound waves to provide an image of your baby in the womb.1 Ultrasound is one of several ways that your health care provider can keep track of your baby’s health and development.

supporting image

When ultrasounds are performed

The majority of women will have an ultrasound in their second trimester when they are 16 to 20 weeks pregnant.1 Some also have a first-trimester ultrasound (also referred to as an early ultrasound) at some point before they are 14 weeks pregnant.1

The ultrasound can be used during pregnancy to show images of your baby, amniotic sac, and placenta. Some major birth defects can be seen with an ultrasound.


How the test works

A prenatal ultrasound test uses high-frequency sound waves transmitted through your abdomen via a device called a transducer to view the inside of your uterus.

The soundwaves are recorded and transformed into video or photographic images of your baby. Your baby's heartbeat and movement of its body, arms and legs can be viewed on the ultrasound.

Most prenatal ultrasound procedures pass the transducer across your abdomen, using a gel as a conductive medium to improve the image’s quality. A transvaginal ultrasound is an alternative procedure performed using a tubular probe inserted into the vagina.

Ultrasound is performed by a doctor or sonographer in your doctor’s office. (Labcorp does not perform ultrasound.)  Ultrasound is a valuable tool and is performed prior to and during a diagnostic procedure like amniocentesis or chorionic villus sampling.  In addition, ultrasound will sometimes identify concerns that might lead your health care provider to offer you a diagnostic test to further investigate the cause of the concern. 

What's not detected

The majority of babies are born healthy.  However, every pregnancy has some risk (3%-5%) of being affected with a genetic disease, birth defect or intellectual disability. Ultrasound studies can identify some, but not all, of these concerns.  

Understanding results

If an abnormality is identified, a follow-up with a specialist like a perinatologist and/or genetic counselor may be recommended.


  1. Ultrasound during pregnancy. March of Dimes website. http://www.marchofdimes.org/pregnancy/ultrasound-during-pregnancy.aspx. Accessed August 2, 2017.