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All about prenatal tests

There are two steps of prenatal testing: Screening tests and diagnostic tests. Read on to find out about these procedures and if it's the right path for you

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Originally published in Today's Parent December 2011

Step 1: Screening tests

There are four basic screening tests in use in Canada. Which one you’re offered will depend on your age, how far along you are in your pregnancy, where you live and, perhaps, your anxiety level, says reproductive geneticist Doug Wilson. Nuchal translucency ultrasound, for example, is not available in most smaller Canadian cities.

First trimester screening (FTS)
This includes a blood test combined with a nuchal translucency ultrasound at 11 to 14 weeks to measure the pocket of fluid at the back of a baby’s neck. An increased thickness is a risk factor for certain conditions, mostly chromosomal abnormalities such as Down syndrome and, sometimes, birth (most commonly heart) defects.
Risks: None.
Accuracy rate: 80 to 85%.
Pros: You get your results early.
Cons: Accuracy not as great as later tests. Doesn’t screen for open neural tube defects.

Integrated prenatal screening (IPS)
Includes a first blood sample and nuchal translucency ultrasound (see definition above) at 11 to 14 weeks, followed by a second blood test at 15 to 20 weeks to check for hormones that can indicate a fetal abnormality.
Risks: None.
Accuracy rate: 85 to 90%.
Pros: Higher accuracy rate than FTS. Screens for open neural tube defects, as well as chromosomal abnormalities.
Cons: Results arrive later than for FTS.

Serum integrated prenatal screening (SIPS)
Includes a first blood sample at 11 to 14 weeks and/or a second blood test (see above) at 15 to 20 weeks.
Risks: None.
Accuracy rate: 80 to 90%.
Pros: Screens for open neural tube defects, as well as chromosomal abnormalities.
Cons: Results arrive later than for FTS.

Maternal serum screening (MSS)
If you haven’t realized you’re pregnant until 3½ months or later, you may only receive the MSS test. It screens for certain chemicals produced by the fetus that appear in the mother’s blood in different amounts than normal when the fetus has Down syndrome. The test comes in either “triple” or “quadruple” screening; quadruple screening is a little more accurate.
Risks: None.
Accuracy rate: 70 to 85% (at the higher end for quadruple screening).
Pros: Can be administered at a later stage of pregnancy. Screens for open neural tube defects, as well as chromosomal abnormalities.
Cons: Results arrive later than for FTS.

Next: Diagnostic tests>

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