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Second-Trimester Fetal Ultrasound: About This Test

Image of an ultrasound of a pregnant woman's belly

What is it?

Fetal ultrasound is a test that 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. (But 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 test 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 do you prepare for the test?

In general, there's nothing you have to do before this test, unless your doctor tells you to.

How is the test done?

  • You may be able to leave your clothes on, or you will be given a gown to wear.
  • You will lie on your back on a padded examination table.
  • A gel will be spread on your belly. It will be removed after the test.
  • A small, hand-held device 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.

What happens after the test?

  • 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?

Go to https://www.healthwise.net/patientEd

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