During pregnancy, all moms will have at least one ultrasound. What does the prenatal ultrasound show? What’s the difference between a 2d and 3D or 4D ultrasound? What happens if the baby doesn’t cooperate on ultrasound day? Le Bonheur Fetal Center Director Janet Tucker, MSN, RNC-OB and Sonographer Jennifer DeClerk, MSHS, RDMS, RVT, RT (R) answer your questions about prenatal ultrasound.

What does prenatal ultrasound tell us?

Many expectant women look forward to the prenatal visit that will include an ultrasound as the first glimpse of their baby. While an ultrasound may be indicated during the first trimester, it is during the second trimester fetal anatomy scan that an expectant mother can see a detailed image of her baby.

The purpose of this exam is:

  • screening for fetal anomalies
  • establish dating
  • identification of any maternal abnormalities that may impact the pregnancy, such as problems with the placenta.

The anatomy scan is usually done between 18-20 weeks gestation. The accuracy of ultrasound allows for detection of major structural anomalies in approximately 60% of ultrasounds.

What is a 3D or 4D ultrasound?

Two-dimensional (2D) ultrasound is used primarily, but 3D and 4D allow for the image to be reviewed and manipulated in different planes for further clarification. This technology is primarily used when an anomaly is found on ultrasound. However, 3D ultrasound is often used to provide mothers an image of the baby’s face.

 The clarity of 3D ultrasound is often appreciated by the expectant family. Sometimes a mother will immediately say “that is her daddy’s nose” or “he looks like my other boys.”  Just as hearing the fetal heartbeat for the first time and the experience of seeing their baby’s image on ultrasound for the first time is valued and may impact bonding.

Why couldn’t we see everything on the ultrasound today?

Gestational age, maternal obesity, fetal movement/position and amniotic fluid level are some of the factors that affect visualizing all of the anatomy. Babies also have sleep cycles and move throughout the day and night. If the baby is in a sleep cycle during the ultrasound exam, they may stay in one position that limits the sonographers’ ability to see all the anatomy.

It is not unusual for an expectant mother to have to return for a repeat scan in a few weeks for completion of anatomy. The sonographer may ask a mom to roll from side to side or to walk around for a few minutes and then try to look again.

What is a Level II scan or targeted scan?

An expectant woman may be referred for a Level II scan when there is a suspicion of a fetal anomaly or when the mother has an increased risk for anomalies due to maternal age, family history or medical conditions. This ultrasound examination is even more detailed than the second trimester fetal anatomy scan and could include a fetal echocardiogram (an in depth view of the heart).

Did you know?

The majority of sonographers have specialized training which can include a bachelor’s degree in diagnostic medical sonography. Sonographers that work in specialized areas like pediatrics or high-risk obstetrics have additional certifications.