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Learning About Birth Defects Testing

What is birth defects testing?

Birth defects testing is done during pregnancy to look for possible problems with the baby (fetus). A birth defect may have only a minor impact on a child's life. Or it can have a major effect on quality or length of life.

You and your doctor will decide which tests are right for you. You may have no tests, one test, or many tests.

Talking with a genetic counsellor may help you make decisions about testing. The counsellor is trained to help you understand these tests. He or she can also help you find resources for support.

What are the types of tests?

You may have a screening test or a diagnostic test. Or you may have both types of tests. Screening tests show the chance that a baby has a certain birth defect, such as Down syndrome, spina bifida, or trisomy 18. Diagnostic tests show if a baby has a certain birth defect.

  • Screening tests and when they are done:
    • Blood tests at 10 to 13 weeks (first trimester)
    • Cell free fetal DNA test at 10 weeks or later (first trimester)
    • Nuchal translucency test at 11 to 14 weeks (first trimester)
    • Triple or quad screening at 15 to 20 weeks (second trimester)
    • Ultrasound at 18 to 20 weeks (second trimester)
  • Diagnostic tests and when they are done:
    • Chorionic villus sampling (CVS) at 10 to 13 weeks (first trimester)
    • Amniocentesis at 15 to 20 weeks (second trimester)

In some cases, the doctors look at the combined screenings that you've had over a period of time. This is called an integrated screening.

What are the screening tests?

  • Blood tests are done to look at different substances in your blood. These tests include cell free fetal DNA and triple or quadruple (quad) blood tests. Both of these tests can help find genetic problems.
  • Nuchal translucency test uses ultrasound to measure the thickness of the area at the back of the baby's neck. An increase in thickness can be an early sign of certain birth defects. Ultrasound is a tool that uses sound waves to make pictures of your baby and placenta inside the uterus.
  • Ultrasound lets your doctor see an image of your baby. It can help your doctor look for problems of the heart, spine, belly, or other areas.

What are the diagnostic tests?

Chorionic villus sampling (CVS) looks at cells from the placenta. To do the test, your doctor may put a thin tube through your vagina and cervix to take out a small piece of the placenta. Or the doctor may take out the piece through a needle in your belly. This test can diagnose many genetic diseases. But it can't find problems with the spinal cord.

Amniocentesis looks at the amniotic fluid that surrounds your baby. Your doctor will put a needle through your belly into your uterus and take out a very small amount of fluid to test.

What are the risks of these tests?

There is a small risk of a miscarriage after a CVS or amniocentesis. Your doctor or genetic counsellor can help you understand this risk. These tests are generally very safe.

Where can you learn more?

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