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.
exactly 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.
the first ultrasound, and what does it look for? This 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.
why are other ultrasounds usually performed? 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 theback 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
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 thighbone is shorter
than normal, it most often is simply a reflection of having short parents
rather than a sign of any abnormality.
ultrasound is often done late in pregnancy to confirm that the baby is head
down and to estimate his size.
some women get more ultrasounds? 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.
happens if something suspicious is seen? In such cases, 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.
an ultrasound 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.
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
an ultrasound can’t guarantee
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.
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