Prenatal Screening for Down Syndrome

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Prenatal Screening for Down Syndrome

What Is Prenatal Screening?

Prenatal screening tests can be a good way to get more information about the risks of certain birth defects in pregnancy. These tests are simple blood tests performed on the mother and are completely safe for the pregnancy. They check the levels of chemicals in the mother's blood to see if they are higher or lower than expected. Sometimes the blood test results are combined with a special kind of ultrasound, called nuchal translucency ultrasound, to calculate a risk.

Prenatal screening tests are designed to pick out pregnancies at higher risk for certain birth defects: Down syndrome, trisomy 18, and spina bifida.

Prenatal screening tests don't test the developing baby directly. They can't tell for sure if there is a birth defect in a pregnancy. Screening tests do pick out those pregnancies at higher risk so that the parents can be offered extra testing.

There are many different types of prenatal screening tests. The tests are different in terms of:

  • when during the pregnancy they are done
  • when during the pregnancy you receive test results
  • what they can tell you
  • their accuracy

Your doctor may recommend one prenatal screening test, or may give you some options to choose from. The information on this site will help you understand both prenatal screening and prenatal diagnostic tests, and decide if you are interested in having them done. Prenatal screening and diagnosis are optional during pregnancy.

Key Things to Know About Prenatal Screening Tests

  • Prenatal screening tests can only tell if a pregnancy has a higher chance for one of these conditions. They can't tell if a pregnancy truly has the condition.
  • If a prenatal screening test comes back "abnormal," it doesn't mean the pregnancy has a birth defect. In fact, most pregnancies that have an "increased risk" result do not have a birth defect.
  • Parents who get an "abnormal" screening test result are offered CVS or amniocentesis to find out for sure if the pregnancy has Down syndrome, trisomy 18, or spina bifida.
  • A "normal" result from screening is reassuring. In general, it means there is less than a 1% chance for the pregnancy to have Down syndrome, spina bifida, or trisomy 18. However, a normal result can't rule out any of these birth defects.
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