Confused about the differences between 2-D, 3-D, and 4-D ultrasounds? Here's everything you need to know about the ultrasound experience.

By 4 Ways With Deviled Eggs
BananaStock/ Jupiter

Getting that first glimpse of your baby on an ultrasound machine is one of the most exciting moments of pregnancy -- perhaps only second to finding out that you're going to be a parent in the first place. Until about a decade ago, a 2-D black-and-white ultrasound, blurry and alien-like, was the only peek most parents got of their little peanut. Now, 3-D ultrasound and even 4-D ultrasound (a real-time moving picture version of a 3-D image) are increasingly available -- at hospitals, ultrasound centers, even the mall! -- so you can marvel over more detailed images. But as cool as it is to see your growing babe, an ultrasound's real purpose is to help your doctor determine whether your pregnancy is progressing normally, says Jude Crino, M.D., director of perinatal ultrasound at Johns Hopkins Medicine, in Baltimore -- and there's more to the latest technology than meets the eye. We asked experts to demystify the ultrasound process.

Getting the Picture

All ultrasounds (or sonograms) use sound waves that bounce off of your little one's body parts to produce an image. Ultrasounds are considered safe, noninvasive, and there are no X-rays involved. During the 15- to 30-minute procedure, the sonographer -- someone trained to do ultrasounds -- rubs gel on your abdomen and then uses a special wand called a transducer that emits the sound waves to create the picture of your baby on the screen. Some ultrasounds are done in a doctor's office with a portable, low-resolution ultrasound machine to check the baby's position and estimate growth. For a more detailed look, however, you'll likely be sent to the hospital or to a specialized ultrasound center where machines with higher resolution can give a more detailed image, which will be read by a specially trained fetal-medicine doctor or radiologist.

Specific Scans

Each ob-gyn practice has its own policy on when to do these higher-resolution ultrasounds (which are still likely to be 2-D), but most doctors recommend two for a typical pregnancy. A first-trimester ultrasound, called a nuchal translucency ultrasound, is done around 12 to 14 weeks to assess the risk of genetic abnormalities such as Down syndrome. (Some patients may also get an ultrasound at around 8 weeks to determine a due date, but that's not standard.) A second ultrasound happens at 18 to 20 weeks and checks fetal anatomy and growth. "We look at about 35 elements, including the brain, heart, kidneys, limbs, face, gender, and more," says Jane Chueh, M.D., director of prenatal diagnosis and therapy at Lucile Packard Children's Hospital Stanford, in Palo Alto, California. But if your pregnancy is considered high-risk -- for example, if you have high blood pressure, diabetes, or are over age 35 -- your doctor may order additional ultrasounds, and perform in-office, low-resolution ultrasounds during your prenatal visits for reassurance, says Dr. Chueh.

New Choices

The most common type of ultrasound is still the traditional 2-D ultrasound -- a single "flat" snapshot that can look blurry to the untrained eye. (The more lifelike 3-D ultrasound is basically lots of 2-D images taken at different angles and stacked together.) Surprisingly, doctors still consider 2-D the gold standard for diagnosing medical issues. "For those of us who have been doing it a while, our brain is wired to conceptualize what it looks like in 3-D," says Joshua Copel, M.D., professor of obstetrics, gynecology, and reproductive sciences at Yale School of Medicine. "The main reason we'd need to use a 3-D scan is if something on the 2-D image doesn't look right."

That said, seeing your baby in 3-D is undeniably momentous, and some practices offer this higher-tech version to parents. "With 2-D, I wasn't sure what I was seeing, but with 3-D the baby was so much more recognizable," says Lee Helland, of New York City. "I actually had been kind of afraid to bond during the pregnancy because I was worried something would go wrong, but seeing her little face and nose, I thought, yup, that's definitely my kid in there. It gave me a new level of comfort."

Bonus Round

If you're not offered 3-D or 4-D and you want it, there are commercial facilities that provide "keepsake imaging" for a fee. Many of these ultrasound studios tailor the experience in ways a doctor's office can't, letting groups watch the ultrasound in a movie theater-like setting, live-streaming the session online, and providing a DVD of the clip set to music. "We invited extended family. It was amazing to have everyone there and to find out the gender all together," says Cyndy Flores, of Austin.

But experts caution that having an ultrasound done for entertainment can be misleading. "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 Dr. Chueh. Plus, while 3-D and 4-D ultrasounds are no more risky than 2-D scans are, 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 Dr. Copel.

No matter what type you get, know that most ultrasounds end in this: a sigh of relief that everything is on track with your baby's development. And if something unusual is picked up, it will help you and your entire medical team prepare for the safest delivery possible.

Copyright © 2014 Meredith Corporation.

Originally published in the August 2014 issue of Parents magazine.

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