Condition Basics

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

What are the types of tests?

You may have a screening test or a diagnostic test, or both. 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.

Should you have birth defects tests?

The decision to test for birth defects is personal. There's a lot to think about, like what the results would mean to you and how they might affect your choices. If you choose testing, you may want to talk with a genetic counsellor to discuss reasons to have or not have the test.

Types of Tests

Testing may be done during pregnancy to look for possible problems with the baby. Birth defects and genetic conditions include:

There are two types of tests for birth defects and genetic conditions.

Screening tests.

These are blood tests and ultrasounds. These tests show the chance that a baby has certain conditions.

Diagnostic tests.

These tests involve taking some of the baby's cells to look at the genes and chromosomes. They can show if a baby has certain conditions.

A screening test can't tell you for sure that your baby has a problem.

• If a screening test result is "negative," it means that your baby probably doesn't have a certain condition. But it doesn't guarantee that you will have a normal pregnancy or a healthy baby.
• If a screening test is "positive," it means that your baby is more likely to have a condition. So you may want to have a diagnostic test to make sure.

If you decide to have screening, you may have only first-trimester tests or only second-trimester tests. Or you may have an integrated screening test. This combines the results of first-trimester and second-trimester tests.

Your doctor or midwife can tell you which tests are available and which ones might be best for you. The tables below are just a guide.

It may not be easy to decide about testing for birth defects or genetic conditions. You may want to talk with a genetic counsellor, who can discuss the reasons to have or not have a test. A counsellor can also help you find other resources for support and decision-making.

Deciding About Testing

The decision to test for birth defects is personal. There's a lot to think about, like what the results would mean to you, and how they might affect your choices.

Some birth defects—like a cleft palate or certain heart problems—can be fixed with surgery after birth. But other defects can't be fixed.

If you choose to have a test, you may want to talk with a genetic counsellor. The counsellor can talk with you about the reasons to have or not have the test. They can also help you find other resources for support and decision-making.

Birth defects testing

Here are some things to think about when deciding to test for birth defects.

• Screening tests can't be used to diagnose a birth defect. They only estimate the chance that your baby has a birth defect. If one of these tests shows a higher-than-normal chance of a birth defect, you would then decide whether to have a diagnostic test such as chorionic villus sampling (CVS) in the first trimester or amniocentesis in the second trimester—to find out for sure if there is a problem.
• Screening tests correctly find most—but not all—cases of Down syndrome. But they sometimes show a higher risk for Down syndrome than is accurate (false-positive result).
• If you plan to have a diagnostic test such as CVS or amniocentesis, you can skip screening tests.
• Screening tests for birth defects can't find every problem a baby could have.

Early fetal ultrasound

Here are some things to think about when deciding about early fetal ultrasound screening.

• Fetal ultrasound is usually done during pregnancy to check the age, size, health, and position of your baby. Most of the time, it is done at about 18 to 22 weeks. If you are sure of your last menstrual period and don't have any risk factors for birth defects, you may not need to have this test any earlier.
• Your doctor or midwife may recommend an early ultrasound if there is a need to find out exactly how long you have been pregnant, if you are having unusual symptoms such as bleeding, or if you have had abnormal results from another test.
• An early ultrasound may show a problem that goes away on its own or isn't important to your or your baby's health. If that happens, you may need to have other tests to find if there really is a problem.
• Some "keepsake video" centres sell ultrasound videos as your baby's first photo. But these centres may use the ultrasound machine at a higher energy level and for longer times than is safe. Health Canada advises against getting a fetal ultrasound if you don't have a medical reason.

Chorionic villus sampling (CVS)

Here are some things to think about when deciding to have a CVS test.

• CVS is done in the first trimester. If the test shows a serious health problem, you have more time to decide whether you want to continue your pregnancy or prepare for care that may be needed.
• CVS isn't a routine test. But your doctor or midwife may recommend it if your chances of having a baby with a genetic condition or birth defect are higher than average.
• Even though CVS can find certain problems, it can't guarantee that your baby will be born healthy. No test can do that.
• CVS has some risks, including a small chance of causing a miscarriage.

Amniocentesis

Here are some things to think about when deciding to have an amniocentesis test.

• Your doctor or midwife may recommend this test if your chances of having a baby with a genetic condition or birth defect are higher than average.
• Even though amniocentesis can detect certain problems, it can't guarantee that your baby will be born healthy. No test can do that.
• If the test shows that your baby may be born with a serious problem, you can decide whether you want to continue your pregnancy or prepare for care that may be needed.
• Amniocentesis is usually very safe. But it does have some risks, including a small chance of causing a miscarriage.

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