What is a fetal ultrasound?
A fetal ultrasound is a test that uses sound waves to create an image of your unborn baby on a video screen. The image helps your doctor know how your baby is doing—and gives you a peek at your baby as well.
When is a fetal ultrasound done?
Your doctor may order an ultrasound scan at any time during your pregnancy. The most common time to have one is between the 16th and 20th week of pregnancy. But you may have an ultrasound earlier in your pregnancy to help determine your due date or check for problems with the baby’s development. And you might have one late in your pregnancy to make sure you have enough fluid in your uterus or to check the baby’s position.
Some women have several ultrasound scans during their pregnancy; some don’t have any. Together, you and your doctor can figure out what will benefit you and your baby.
What information does a fetal ultrasound provide?
An ultrasound can help your doctor determine how far along you are in your pregnancy. It may verify or change your expected due date. The ultrasound may show your baby's sex, heart rate, breathing, movements and position in the uterus. But if you’re not very far along in your pregnancy, the ultrasound may not be able to show all these things. The ultrasound also can show if you are having more than one baby.
Your doctor can use an ultrasound to look for problems with the pregnancy. The amount of amniotic fluid, the size and position of the placenta, and the condition of your uterus and other organs may be examined. If the scan suggests a problem, your doctor can order other tests and then decide whether you and your baby need special care for the rest of your pregnancy.
How accurate are fetal ultrasounds?
No test is completely free from error. It is possible an ultrasound might not find a problem that exists, or it might suggest a problem that isn't really there.
Are fetal ultrasounds safe?
Ultrasound testing has been used for many years, and no harm to an unborn baby has ever been reported. However, nonmedical use of ultrasound by businesses that sell "keepsake" pictures of the unborn baby may not be a good idea because they could give incorrect information. These businesses may use untrained technicians who are not supervised by doctors, and experts advise against using them.
Where will I go for an ultrasound?
The ultrasound should be performed in your doctor's office, an imaging center or a hospital. A doctor or a trained technician who works under a doctor’s supervision will do the scan.
What does it feel like to have a fetal ultrasound?
You will lie down on a padded table. For a standard ultrasound, the doctor or technician will spread a gel on your belly, then rub a hand-held device called a transducer over the belly. The gel helps transmit the sound waves from the transducer into your body.
The sound waves bounce off bodily structures and your baby, and the transducer receives the sound waves that bounce back. Those sound waves are used to create images on a TV screen or computer monitor. White or grey areas in the images show bone and tissue, while dark areas show liquid, such as the amniotic fluid around the baby. It may be hard for you to see your baby in the images, so your doctor or technician may explain what the images show. You'll likely be given some printed copies to take home. The exam may take about 20 minutes or longer.
You will probably be asked to keep your bladder full before and during the ultrasound, which can cause some discomfort. You will not be able to feel the sound waves, but the movement of the transducer may create a little pressure on your belly. You might hear the sound waves—and maybe your baby’s heartbeat—through the monitor. If your pregnancy is past the 18th week, your baby might be able to hear some vibrations from the procedure. These are not harmful to the baby.
When will I get the results?
Some of the results of your ultrasound will be available immediately, while the doctor or technician is still performing it. Other results may need to be analyzed by your doctor, which can take a week or longer.
Are there other types of fetal ultrasound?
Yes. You may have another type of ultrasound if you have certain risk factors, or if your doctor needs to get a better look at your baby. They include:
- Transvaginal ultrasound. A transducer is placed in the vagina in addition to or instead of being rubbed over the belly. This may provide a better image in early pregnancy because the uterus is still small and close to the vagina.
- Doppler imaging. This type of test measures how well blood is flowing in your baby’s body. It may be used if you have high blood pressure or if your baby's growth is slower than normal. Many ultrasound machines include Doppler imaging, so you may have both tests at the same time.
- Fetal echocardiography. This type of ultrasound gives a more detailed picture of your baby’s heart. The test may be used to check your baby for heart defects.
- Three-dimensional (3-D) ultrasound. This creates images that look more lifelike than standard ultrasound images do. These images can give doctors and technicians a better look at how your baby is developing.
- Four-dimensional (4-D) ultrasound. This is 3-D ultrasound that also records your baby’s movement.
Written by familydoctor.org editorial staff