Fetal ultrasound uses sound waves to make pictures of the fetus and placenta inside the uterus. The test is the safest way to find out the age, size, and position of your baby. During the test, a small handheld device called a transducer is passed over your belly. If ultrasound is done before the 11th week of pregnancy, a transducer shaped to fit inside your vagina may be used.

Fetal ultrasound is usually done at about 18 to 22 weeks of pregnancy. If you are sure of your last menstrual period and don't have any risk factors for birth defects, you probably don't need to have this test any earlier.

A combination of tests that includes ultrasound may be done during your first trimester to check for Down syndrome. This first-trimester screening test is different from the routine ultrasound that is usually done at about 18 weeks of pregnancy. It uses an ultrasound measurement of the thickness of the skin at the back of the baby's neck (nuchal translucency).

If your doctor recommends that you have an early fetal ultrasound (before 18 to 22 weeks), the test may give you some useful information.

• If the test doesn't show any problems, you may feel more at ease during your pregnancy.
• If you learn that you are carrying more than one baby, you and your doctor can plan ahead for a healthy pregnancy and delivery.
• If you find out that the baby has a problem, then you, your partner, and your doctor can talk about your choices. The first step may be to repeat the ultrasound or have other tests to confirm the results.
  • Some problems can be treated soon after the baby is born. They may not seriously affect your baby's life. You may be able to plan your delivery in a hospital that offers special care for sick newborns.
  • Some problems, such as certain types of neural tube defects and Down syndrome, may not be fatal. But they will affect your baby for their entire life.
  • In rare cases a defect is so severe that the baby may not survive the pregnancy or may die soon after birth.
  • Sometimes a possible defect is suspected but not confirmed, and the baby is born perfectly healthy.

The decision about what to do if you find out that you are carrying a baby with a severe defect is very personal. Some women who learn that their baby has a serious defect choose to end their pregnancy. Others make plans for raising a sick or disabled child.

Fetal ultrasound is a safe test when it's performed for medical reasons by a trained ultrasound technologist or a doctor.^{footnote 1}

Abnormal results from an early fetal ultrasound can cause a lot of stress and anxiety. For example:

• They can require more tests to find out if there really is a problem. You might need another ultrasound or amniocentesis. Most of the time, the results from these extra tests are normal. But extra tests can carry risks. Amniocentesis has more risks than ultrasound, including a very small risk of miscarriage.
• They can show a problem that goes away later in your pregnancy.
• They may show a serious problem when there isn't one. But you may need more tests before you know this for sure. It can be stressful while you wait to find out.

Some "keepsake video" centers sell ultrasound videos as your baby's first photo. But these centers may use the ultrasound machine at a higher energy level and for longer times than is safe. The U.S. Food and Drug Administration advises against getting a fetal ultrasound unless there is a medical reason.

If you don't have an early ultrasound, there is a slight chance that you may not find out until later that:

• You are carrying more than one baby.
• Your baby has a birth defect. In rare cases, a defect is so severe that the baby may not survive the pregnancy or may die soon after birth. Some women choose to end a pregnancy rather than suffer a stillbirth or death of a newborn.

Your doctor may recommend an early ultrasound if:

• You have bleeding or other symptoms of miscarriage.
• You have risk factors for birth defects. An ultrasound can check for birth defects that affect the baby's brain and spinal cord.
• There is a need to find out exactly how long you have been pregnant.
• You have had another test that suggests a possible problem with the fetus.