Second-Trimester Fetal Ultrasound: About This Test

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Image of an ultrasound of a pregnant woman's belly

What is it?

Fetal ultrasound uses sound waves to make pictures of your baby (fetus) and placenta inside the uterus. The test is the safest way to find out the age, size, and position of your baby. You also may be able to find out the sex of your baby (although the test isn't done just to find out a baby's sex).

No known risks to the mother or the baby are linked to fetal ultrasound. But you may feel anxious if the ultrasound reveals a problem with your pregnancy or baby.

Why is this test done?

In the second trimester, a fetal ultrasound is done to:

  • Estimate the number of weeks and days a fetus has developed since the beginning of the pregnancy. This is called the gestational age.
  • Look at the size and position of the fetus, the placenta, and the fluid that surrounds the fetus.
  • Find major birth defects, such as heart problems or problems with the brain and spinal cord (neural tube defects). But the test may not be able to find many minor defects and some major birth defects.

How can you prepare for the test?

  • You may need a full bladder for the test. If so, you will be asked to drink water or other liquids just before the test and to avoid urinating before or during the test.

What happens during the test?

  • You may not need to remove your clothes for this test. You can lift your shirt and push down the waistband of your skirt or pants. If you are wearing a dress, you will be given a cloth or paper covering to use during the test.
  • You will lie on your back on a padded examination table.
  • A gel will be spread on your belly.
  • A small, handheld instrument called a transducer will be pressed against the gel on your skin and moved across your belly several times.
  • You may watch the monitor to see the picture of your baby during the test.
  • The test takes 30 to 60 minutes.

What else should you know about the test?

  • You may not get the test results right away. You can usually get full results in 1 or 2 days.

What happens after the test?

  • The gel will be cleaned off your skin.
  • You will probably be able to go home right away.
  • You most likely will be able to go back to your usual activities right away.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

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