All about ultrasounds

Reviewed by the BabyCenter Medical Advisory Board

What is an ultrasound?
An ultrasound (also called a sonogram) is a noninvasive diagnostic test that uses sound waves to create a visual image of your baby, placenta, and uterus, as well as other pelvic organs. It allows your healthcare practitioner to gather valuable information about the progress of your pregnancy and your baby's health.During the test, an ultrasound technician (sonographer) transmits high-frequency sound waves through your uterus that bounce off your baby. A computer then translates the echoing sounds into video images that reveal your baby's shape, position, and movements.The series of television-monitor images is called a sonogram. The words ultrasound and sonogram are often used interchangeably. (Ultrasound waves are also used in the handheld instrument called a Doppler that your practitioner uses during your prenatal visits to listen to your baby's heartbeat.)Most moms-to-be have a standard ultrasound when they're between 16 and 20 weeks pregnant. But you may have one as early as 4 or 5 weeks or any time after that if there are signs of a problem. Most people look forward to the midpregnancy ultrasound because it gives them a first glimpse of their baby.The technician will probably present you with a grainy printout of the sonogram as a keepsake. And you may be able to find out your child's sex, if you want to. But the main purpose of the ultrasound is to provide you and your practitioner with important information about your baby's health and development.If you're having a low-risk pregnancy, however, you might not be offered an ultrasound at all. In fact, the American College of Obstetricians and Gynecologists recommends ultrasounds only when there's a specific medical reason. According to the March of Dimes, about 70 percent of pregnant women in the United States have an ultrasound.

What information will my ultrasound provide?
During a typical midpregnancy sonogram, with the help of a sonographer, your practitioner will:Check your baby's heartbeatTo make sure it's normal, she'll measure the number of beats per minute.Confirm your baby's locationThis is to make sure your baby's growing inside your uterus and your pregnancy isn't ectopic, meaning the embryo is lodged in a fallopian tube or elsewhere other than the uterus. But in most cases, you would have had symptoms of an ectopic pregnancy early on and a scan done at that point to confirm the problem.Measure your baby's sizeThe sonographer will measure your baby across the skull, along the thighbone, and around the abdomen in an attempt to make sure he's about the size he should be for his age. If this is your first ultrasound and your baby is more than two weeks behind or ahead of where he should be, sizewise, it's likely that your due date is off and you'll be given a new one. If your practitioner has any concerns about how your baby is growing, she'll order one or more follow-up ultrasounds to check his progress.Check to see if there's more than one babyBy now you'll probably already know if you're carrying twins or higher multiples. Most women pregnant with multiples measure large in their first trimester and have an ultrasound at that point to confirm the number of babies.Check the location of the placentaIf the placenta is covering the cervix (placenta previa), it can cause painless but severe bleeding later in the pregnancy. If your practitioner detects this condition, she'll most likely order a follow-up scan early in your third trimester to see if the placenta is still covering the cervix. In the meantime, don't panic! Only a small percentage of placenta previas detected on an ultrasound before 20 weeks are still there at delivery.Assess the amount of amniotic fluid in the uterusIf the sonogram shows that you have too much or too little amniotic fluid, there may be a problem. You'll have a complete work-up to see if the cause can be identified, and your practitioner may want to monitor you with regular ultrasounds.Check the baby for physical abnormalitiesYour practitioner will look closely at your baby's basic anatomy, including his head, neck, chest, heart, spine, stomach, kidneys, bladder, arms, legs, and umbilical cord to make sure they're developing properly. If you've had any suspicious results from a multiple marker or first trimester screening, or if there's any other cause for concern, the technician will do a more thorough (level II) scan to check for signs of a birth defect or Down syndrome.Try to determine your baby's sexIf you'd like to find out whether your baby's a boy or a girl, you usually can at the midpregnancy ultrasound (16 to 20 weeks), unless, for example, your child's hand is covering his genitals during the scan. In some cases, it's important for your practitioner to know your baby's sex — for example, if the baby is thought to be at risk for certain congenital conditions.Let your technician know if you don't want to know your baby's sex so that she doesn't give the surprise away during the test.An ultrasound may also be done at other times during your pregnancy to check on your baby's condition; as part of other tests, such as the nuchal translucency test, chorionic villus sampling, or amniocentesis; or as a follow-up to the multiple marker test.

Why would I need an ultrasound during my first trimester?
Some practitioners routinely recommend an ultrasound at about 7 to 9 weeks, but others will only do one if they have reason to suspect any of the following:MiscarriageIf you have vaginal bleeding early in your pregnancy, your practitioner may be concerned about miscarriage and want to schedule an ultrasound to check on your baby. The baby's heartbeat should be clearly visible by 6½ weeks of pregnancy (assuming a 28-day menstrual cycle). If you can see the baby's heart beating on the sonogram after 7 weeks, your chances of continuing with the pregnancy are greater than 97 percent.If you don't see the heart beating at this point, don't despair. It may be that your cycle is longer than average and your baby is younger than your practitioner figured. She may want to try again in a week.Ectopic or molar pregnancyVaginal bleeding (as well as other symptoms) can also indicate an ectopic or molar pregnancy. In the case of an ectopic pregnancy, which occurs when the embryo isn't in the uterus, your practitioner will try to determine where the embryo is. In a molar pregnancy, in which there's abnormal placenta and usually no viable baby, the ultrasound may show what appears to be a cluster of grapes where the baby should be.Uncertain gestational ageIf you're unsure of the date you started your last menstrual period or the length of your cycle, your practitioner may suggest an ultrasound at 7 weeks to see how far along you really are.Since all fetuses are about the same size in their early weeks, your practitioner can usually determine your baby's gestational age (and thus your approximate due date) by taking certain measurements. When you're between 7 and 13 weeks, measuring from the crown of your baby's head to his rump will allow her to determine the baby's age within three or four days.Multiple gestationIf you're measuring large (or if you've had fertility treatments), you may be pregnant with twins or higher multiples. Your practitioner will order an ultrasound to see how many babies you're carrying.

Why would I need an ultrasound later in my pregnancy?
These are the most common reasons your practitioner would order a third-trimester ultrasound:To determine the cause of vaginal bleedingBleeding during the second half of your pregnancy may be caused by problems with the placenta. An ultrasound can help your practitioner figure out what's going on.To check on your baby's growthLater in pregnancy, if there's any concern that your baby is not growing properly, your practitioner may schedule an ultrasound (or a series of them) to measure certain parts of his body. In particular, she'll be measuring the size of your baby's head, the length of his thigh bone, and the distance around his midsection.To check on your amniotic fluid levelIf you've been diagnosed with too much or too little amniotic fluid, your practitioner will probably order regular ultrasounds throughout your third trimester to monitor your baby's condition.To check on your baby's well-being late in the pregnancyIf you have high blood pressure or diabetes, or you're overdue, your practitioner may order a biophysical profile to check on your baby's movements and breathing and to measure the amount of amniotic fluid.To determine whether you should plan for a cesarean sectionThis may be the case if your baby is especially large (particularly if you have diabetes) or in an abnormal (breech) position, or if the placenta is blocking your baby's way out of the uterus.

What's the procedure like?
Ultrasound scans are usually done through the abdomen, but they may also be done through the vagina. For a trans-abdominal scan, you lie on your back on an examination table with your abdomen exposed and an assistant rubs cool gel over your tummy to improve the sound conduction. Then the sonographer slides the transducer (which looks a little bit like a telephone receiver) back and forth over your stomach to transmit sound waves. As a computer translates the resulting echoes into pictures on a television monitor, your baby appears on the screen before your eyes.During the scan, the sonographer records your baby's measurements and takes still pictures or video for your caregiver to interpret. While you may be eager to know what she's seeing, you may need to wait until your practitioner has seen the results and can discuss them with you. If you'd prefer not to know your baby's sex, be sure to tell the sonographer before she blurts it out.A basic ultrasound takes about 15 to 20 minutes. A more detailed (level II) scan, which may use more sophisticated equipment, can take anywhere from 30 minutes to 90 minutes or more.First-trimester ultrasounds are more likely to be done through the vagina these days, with a specially designed probe. This method may be somewhat uncomfortable, but in the early stages of pregnancy, it generally provides better images than a trans-abdominal one and can be very useful in diagnosing ectopic pregnancies and fetal abnormalities.If you're having a trans-abdominal ultrasound during your first trimester, you may be asked to drink several glasses of water ahead of time so that you have a full bladder during the procedure. This can be quite uncomfortable.

What about 3-D ultrasound?
You may have heard about the new 3-D ultrasounds that use special equipment to show a view of your baby that's almost as detailed as a photograph. Some experts say that the technique allows more accurate evaluation of problems such as spina bifida and cleft palate. But the new technology requires a more skilled sonographer and isn't available yet in many places.Some centers offer 3-D ultrasounds solely to create keepsake photos or videos for parents. Remember that the personnel at these places may not be qualified to counsel you if your ultrasound reveals a problem. And since the scan is for "entertainment only," the results may be falsely reassuring.

Does it really matter where I have my ultrasound done?
Sonograms done at state-of-the-art academic centers can detect abnormalities up to 80 percent of the time, while at sites such as doctor's offices — which tend to have lower-tech equipment and less-experienced personnel — the detection rate can dip as low as 13 percent. So consider requesting a "registered medical diagnostic sonographer" to administer your ultrasound and a radiologist or obstetrician who specializes in ultrasound to interpret the results, especially if other tests have raised suspicions about possible problems.

Are there any risks or side effects from this procedure?
Numerous large studies done over the last 35 years have found no evidence that ultrasounds harm developing babies, or that there's a cumulative effect from having multiple scans. And reports from some small studies suggesting the procedure increases the chance of low birth weight, speech and hearing problems, and left-handedness haven't been borne out by more rigorous research.

What if the ultrasound shows a problem?
Don't panic. Often, a follow-up test shows that a suspicious ultrasound is no cause for concern. But in the unlikely event that your baby has a health problem, the information from the ultrasound can help your practitioner determine how to give your baby the best outcome possible.For example, serious heart rhythm problems can be treated with medication while the baby is still in the womb. Other abnormalities, such as a urinary tract blockage, can be treated by surgery even before birth. And knowing about other birth defects can help your practitioner decide how to deliver the baby safely and prepare to care for him right after birth.In any case, it allows you to consider all the options, whether that means making the difficult decision to terminate a pregnancy, intervening medically, or preparing for the birth of a baby who needs special care. A genetic counselor can help answer a lot of your questions.