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An ultrasound scan may be your first peek at your baby. If you have one at an early prenatal checkup, you may hear your baby's heartbeat for the first time. Ultrasound will reveal a lot more at midpregnancy, including your baby's sex, if you want to know it. It's is also used for genetic tests and to monitor medical complications.
What is an ultrasound?
A prenatal ultrasound scan uses sound waves to create a visual image (sonogram) of your baby, placenta, and uterus during pregnancy. 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) uses a handheld instrument called a transducer to send sound waves through your uterus. These waves bounce off your baby, and a computer translates the echoing sounds into video images that reveal your baby's shape, position, and movements.
(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.)
When will I have an ultrasound?
You may have an early ultrasound at your practitioner's office in your first trimester to confirm your pregnancy and check how far along you are. Or you may not have one until the standard midpregnancy ultrasound between 18 and 22 weeks. That's when you may learn your baby's sex if you like. (The technician will probably present you with a grainy printout of the sonogram as a keepsake.)
You may also have a sonogram as part of a genetic test, such as the nuchal translucency test, chorionic villus sampling, or amniocentesis, or at any other time if there are signs of a problem with your baby. You'll have more frequent ultrasounds if you have diabetes, hypertension, or other medical complications.
What happens at a first trimester ultrasound?
When you call your healthcare provider to schedule your first prenatal appointment, ask whether you'll be having an ultrasound. More and more practitioners have ultrasound equipment in their office and are doing ultrasounds for their patients as early as 6 to 10 weeks.
Bring your partner with you if you can. You're likely to see the baby's heart beating if you're at least 6 weeks pregnant. If you're 8 weeks along, you should be able to hear your baby's heartbeat as well. (If you don't see the heart beating, don't despair. It may be that you're not as far along as you thought.)
If you're unsure of the date you started your last menstrual period or the length of your cycle, your practitioner may use ultrasound to see how far along you 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.
You'll also be able to find out if you're pregnant with twins (or more!)
First-trimester ultrasounds are sometimes done through the vagina with a specially designed wand. This method may be somewhat uncomfortable, but don't worry – it's just as safe as a typical transabdominal ultrasound. And in the early stages of pregnancy, a transvaginal ultrasound generally provides better images.
It also makes it easier to diagnose early pregnancy problems, such as amiscarriage or a molar or ectopic pregnancy.
What information does a midpregnancy ultrasound provide?
A midpregnancy sonogram allows your practitioner to:
Check your baby's heartbeat
To make sure the heartbeat is normal, your healthcare provider measures the number of beats per minute.
Measure your baby's size
The sonographer will measure your baby across the skull, along the thighbone, and around the abdomen 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 bigger or smaller than he should be, 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 the location of the placenta
If the placenta is covering the cervix (placenta previa), it can cause 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 posing a problem when the baby is due.
Check your cervical length
A short cervix may put you at risk for preterm delivery. When detected early on, interventions such as progesterone or cerclage may prove helpful.
Assess the amount of amniotic fluid in the uterus
If 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 abnormalities
Your 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 test 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 sex
If you'd like to find out whether your baby's a boy or a girl, you usually can at this time, 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 spoil the surprise during the test.
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 bleeding
Bleeding 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 growth
Later in pregnancy, if there's any concern that your baby is not growing properly, or if you have medical conditions like diabetes that can cause growth abnormalities, 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 your amniotic fluid level
If 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 pregnancy
If 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 section
You may need to schedule a cesarean section 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 it like to have an ultrasound?
Come to your ultrasound with a full bladder. The bladder helps push your uterus up out of the pelvis and makes the ultrasound easier to perform through the abdomen.
For a transabdominal scan, you lie on your back on an examination table with your abdomen exposed. An assistant puts cool gel over your belly to improve the sound conduction. Then the sonographer slides the transducer (the handheld device, which is about the size of a bar of soap) back and forth over your stomach. The transducer transmits sound waves, and a computer translates the resulting echoes into pictures on a video monitor, making your baby appear on the screen before your eyes. Bone is white, fluid is black, and soft tissue organs appear as shades of gray.
During the scan, the room will be darkened so that the images can be clearly seen on the screen. The sonographer records your baby's measurements and takes still pictures or video for your caregiver to interpret. You can watch the process on the screen, if you like. (If you'd prefer not to know your baby's sex, be sure to tell the sonographer before you start.) While you may be eager to talk about what she's seeing, you may need to wait until your practitioner has seen the results and can discuss them with you.
Anatomy ultrasounds usually take 45 minutes to complete, but a more detailed (level II) anatomy scan, which may use more sophisticated equipment, can take anywhere from 45 to 90 minutes or more. Growth ultrasound may take 15 to 20 minutes, and a biophysical profile takes about 30 minutes.
What about 3-D and 4-D ultrasound?
You may have heard about 3-D ultrasounds that use special equipment to show a view of your baby that's almost as detailed as a photograph. (They do this by taking thousands of images at once.)
This technology may be helpful in viewing certain fetal abnormalities but is not medically necessary in the majority of cases.
Some centers (often found in malls and certain private offices) 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.
Four-dimensional ultrasounds can capture the baby's movement. These are rarely used for medical purposes.
Is it safe to have extra ultrasounds?
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. (Ultrasounds don't involve radiation, like X-rays do.).
At the same time, experts caution against unnecessary ultrasounds, pointing out that while there are no known negative effects to date, ultrasounds are a form of energy, and it's conceivable that they affect the developing baby. This may be especially true during the first trimester, when the baby is more susceptible to external factors.
Bottom line: Don't be afraid to have a sonogram when you need one, but don't have one just for fun.
Does it 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.
If problems are suspected in your pregnancy, you may be referred for a more detailed ultrasound that will be interpreted by a radiologist or maternal-fetal medicine specialist (MFM).
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, being informed 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.
There are people who can help you navigate the results of a concerning ultrasound. A genetic counselor can help answer a lot of your questions and help guide you through your decision making.