Ultrasound Exams: What to Expect
Ultrasound exams are routine during pregnancy, but how much do you actually know about them? Here's how they work and what they can tell you.
Among the most memorable pregnancy moments are those when you see your developing baby on the ultrasound monitor. That flickering heartbeat! Those tiny fingers and toes! But ultrasound exams (aka sonograms) 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.
And in the minority of cases when something serious is suspected or detected, ultrasounds can provide essential information before a baby is born. To help demystify the process, here are answers to the most common questions about ultrasound exams.
What is 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. During a typical exam, a gel is spread on your abdomen to help conduct the sound waves, and the doctor or, more often, an ultrasound technician glides a transducer around your belly while watching and capturing the images. She'll likely give you a talking tour of your baby's body and capture several hard-copy photos for you and the doctor.
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When will I get an ultrasound?
An ultrasound exam can be given at any time during your pregnancy. You may even have multiple ultrasounds throughout your pregnancy, to help track the development and health of the baby. Women whose pregnancies are considered high-risk due to diabetes, carrying multiples, or other conditions may have more frequent ultrasounds to measure the baby's growth or assess fetal movement, tone, and breathing. But some practitioners simply prefer doing additional ultrasounds for all their patients to keep tabs on the baby's growth and development.
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 vaginal 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.
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 clear (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.
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.
An ultrasound is often done late in pregnancy to confirm that the baby is head down and to estimate his size.
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What if the ultrasound technician notices something suspicious?
If something suspicious is seen, an ultrasound technician is not 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.
Can ultrasounds determine the baby’s sex?
Depending on the fetus's position, gender can usually be determined accurately during the anatomical survey, though sometimes it can be done earlier. Be sure to tell the ultrasonographer in advance if you don't want to know your baby's sex.
Do ultrasounds pose any risks to mother or baby?
There are no known risks, 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.
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3 things an ultrasound can't guarantee
1. An accurate prediction of your baby's birth weight. Even when an ultrasound is done close to your due date, estimates of the baby's size can be off by as much as a pound or even more.
2. That a baby will not have a birth defect. The ability to detect an abnormality depends on a number of factors, including the fetus's gestational age, size and position, the amount of amniotic fluid, the type of equipment used and the nature of the defect.
3. A complete anatomical picture of the fetus if you are obese. Having excess body fat can interfere with an ultrasound's ability to create a clear image of the baby.