Your Guide to Baby Ultrasound Exams

Ultrasound exams are routine during pregnancy, but how much do you actually know about them? Here's an expectant mom's guide to baby ultrasounds. 

Pregnant woman having fetal ultrasound
Photo: Lighthunter/Shutterstock

Most mothers-to-be love watching their developing baby on the ultrasound monitor. That flickering heartbeat! Those tiny fingers and toes! But ultrasound exams can also be mysterious and nerve-wracking.

"Some women come in thinking nothing could be wrong, and others come in worrying about everything," says Joanne Stone, M.D., a professor of obstetrics, gynecology, and reproductive Science at Mount Sinai School of Medicine in New York. Fortunately, she adds, most women have totally normal ultrasounds, and even when there is an unusual finding, it often just suggests a slightly increased risk of a rare condition.

To help demystify the pregnancy ultrasound process, here are the answers to some commonly asked questions.

What is the Ultrasound Procedure?

During an ultrasound, high-frequency sound waves are sent into your uterus, where they bump into the fetus's tissues and echo back. A computer analyzes the echoes and transforms them into black-and-white images on a monitor.

Gel is usually spread on your abdomen to help conduct the sound waves, and the ultrasound technician glides a transducer around your belly while watching the images.

Don't know how to read an ultrasound? No worries—the technician will tell you about your baby's developing body during the exam. She’ll also capture several hard-copy photos for you and the doctor.

What is Ultrasound Used For?

Ultrasounds have many applications in pregnancy. According to the American College of Obstetricians and Gynecologists, ultrasounds are usually prescribed for the following reasons:

  • To establish the baby's age: Early in pregnancy, ultrasound helps accurately date a pregnancy, preventing unnecessary interventions.
  • To identify fetal abnormalities: Since it allows the physician to see the baby's developing body in great detail, an ultrasound is key in the detection of fetal abnormalities.
  • To determine the position and size of the baby: Toward the end of pregnancy, a doctor can see a baby in breech position and determine if he’s too big to fit through the mother's pelvic cavity.
  • To detect multiple pregnancies: Scans help confirm multiple pregnancies and assess the babies' growth and health.
  • To perform chorionic villus sampling (CVS) or amniocentesis: An ultrasound helps safeguard certain genetic-testing procedures by allowing the doctor to ascertain the safest place to insert a catheter or needle.
  • To assess pregnancy complications: Ultrasound helps the physician see the source of abnormal pregnancy bleeding and identify possible complications such as placenta previa.

When Will I Get Baby Ultrasounds?

An ultrasound can be given at any time during your pregnancy. You may even have multiple ultrasounds to track the development and health of the baby. Women whose pregnancies are considered high-risk (due to gestational diabetes, carrying multiples, or other conditions) may have more frequent ultrasounds to measure the baby's growth or assess fetal movement, tone, and breathing.

Here is a general guide on the baby ultrasound timeline.

First Ultrasound (Weeks 6 or 7): The first ultrasound is typically performed around week six or seven (usually at your first prenatal visit) to locate the heartbeat and estimate the age of the fetus. "Most women are more excited than nervous during this exam," Stone says. It's also done to rule out multiples or an ectopic pregnancy—one that develops outside of the uterus.

Sometimes a transvaginal ultrasound is performed at this early stage. For this, you lie back as if you're having a pelvic exam and a narrow wandlike device is inserted; the procedure is painless.

First Trimester Screening (Weeks 11 to 13): Typically, an ultrasound is done between weeks 11 and 13 as part of the first-trimester screening for chromosomal abnormalities, including Down syndrome. (The other part of the screening consists of a blood test.) The nuchal translucency, or NT, test uses ultrasound to measure the translucent space in the tissue at the back of the fetus's neck. Babies with chromosomal abnormalities tend to have more of this tissue than others. However, Stone says, "This is just an indication of risk, not a diagnosis of Down syndrome." For a definitive diagnosis, a follow-up procedure such as amniocentesis is required. This ultrasound also looks at the size and position of the placenta and the level of amniotic fluid.

Anatomy Ultrasound/ Anatomical Survey (Weeks 18-20): Another commonly performed ultrasound is the anatomical survey, done at weeks 18 to 20. This is a head- to-foot scan that looks for any abnormalities or growth problems. "Women tend to be nervous during this scan because they don't know what may be found," Stone says. "But when I do find something, I'm usually able to reassure a patient," she adds. For example, if a baby's thigh bone is shorter than normal, it most often is simply a reflection of having short parents rather than a sign of any abnormality.

Late Pregnancy Ultrasound: An ultrasound is often done late in pregnancy to confirm that the baby is head down and to estimate his size.

Help—My Pregnancy Scan Has Abnormal Results!

If something suspicious is seen on your fetal ultrasound, the technician isn’t allowed to say anything to the patient, so try not to bombard her with questions. Typically, the doctor reviews all pictures, often in real time, and he or she will meet with you during or right after the ultrasound to discuss any findings.

In larger medical centers, a genetic counselor may be immediately available to discuss issues of risk and your options if a problem is found, or you may be referred to speak to someone the next day, says Ellen Landsberger, M.D., an associate professor of obstetrics and gynecology at the Albert Einstein College of Medicine and Montefiore Medical Center in the Bronx, N.Y.

What’s the Difference Between a Sonogram and Ultrasound?

At some point, all pregnant women wonder about the sonogram vs. ultrasound debate. Here’s the deal: Although “sonogram” and ”ultrasound” are often used together, they aren’t the same thing. An ultrasound is the procedure used to create an image of your fetus; a sonogram is the actual image itself. The practice of giving and interpreting ultrasounds is called “sonography.”

Are Ultrasound Procedures Safe?

There are no known risks to baby ultrasounds, but there's no way to guarantee safety either. That's why doctors are cautious about not overusing the diagnostic tool or treating it like entertainment. "We follow the safe principle of using the lowest-frequency sound waves possible," Landsberger says.

Types of Ultrasounds: 2D, 3D and 4D Exams

Until about a decade ago, the traditional two-dimensional black-and-white ultrasound—blurry and alien-like—was the only peek most parents got of their little peanut. Now, 3D ultrasounds let you see your baby with a sharper, life-like quality. Some practices even offer 4D ultrasounds, which are basically a real-time moving video of your baby.

Both 3D and 4D ultrasounds have many benefits. For example, they help doctors diagnose abnormalities and birth defects, says Michele Hakakha, M.D., an OB-GYN in Beverly Hills and author of Expecting 411. They also give parents a clearer look at their baby-to-be.

These advanced types of ultrasounds also come with some drawbacks—mainly that commercial facilities have started to offer “keepsake” 3D ultrasound imaging for expecting parents. And while medical ultrasounds are generally considered safe, there’s little information about the effect of long-term, non-medical exposure to ultrasound technology on babies. "These facilities could miss an anomaly, giving you a false sense of security, or they could say something that makes you think something's not right, causing unnecessary anxiety," points out Jane Chueh, M.D., director of prenatal diagnosis and therapy at Lucile Packard Children's Hospital Stanford, in Palo Alto, California.

Both the American Congress of Obstetricians and Gynecologists and the American Institute of Ultrasound in Medicine advise doctors to use ultrasound only when it's medically necessary. "It's difficult to prove absolute safety, and ultrasound does expose the fetus to a form of energy, so we recommend using it only if there's a medical benefit," says Joshua Copel, M.D., professor of obstetrics, gynecology, and reproductive sciences at Yale School of Medicine.

Updated by Nicole Harris
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