Testing before becoming pregnant

You may want to consider genetic testing for Down syndrome if you are planning to become pregnant and you have a family history of the condition. Genetic testing can confirm whether you or your partner carry the translocation chromosome, which increases your risk for having a child with the translocation type of Down syndrome. But this kind of testing does not detect whether your child is more likely to have the trisomy 21 type, which accounts for most Down syndrome cases.

Genetic counseling can help you understand why genetic testing is done, what the results mean, and how the results may affect you and your family.

Screening during pregnancy

Screening does not diagnose Down syndrome but rather provides information about the likelihood that your fetus will have the condition. Screening tests include:

• Fetal ultrasound. This test can detect signs of Down syndrome in the first trimester. A fetal ultrasound image can show a greater-than-normal amount of fluid at the back of a fetus's neck. The skin fold thickness measurement estimates the distance between the surface of the skin and the neck bones (nuchal fold). This test is not yet widely available, because only a specially trained provider can do it.
• Maternal serum triple or quadruple screen test. The triple test (triple screen) is done in the second trimester. It measures the amounts of the following 3 substances in your blood:
  • Alpha-fetoprotein (AFP)
  • Human chorionic gonadotropin (hCG)
  • Estriol (uE3)

The test is called a quadruple screen (quad screen) when a test for inhibin A is added. Inhibin A is a protein that is produced by the fetus and the placenta. The quadruple test can detect most Down syndrome cases, and it may be less likely than the triple screen to deliver false-positive results.⁶ The triple and quad tests can only be done in the second trimester.

Should I have the maternal serum triple test or quadruple test (triple or quad screen)?

Other screening options that may be available in the first trimester include:

• Combination screening.
• Integrated screening.

A combination screening uses both a fetal ultrasound and a blood test to measure levels of human chorionic gonadotropin (hCG) and pregnancy-associated plasma protein-A (PAPP-A). It has shown to be as exact as the quad screen for detecting Down syndrome.⁷ One advantage of this type of screening is that it can be done earlier in your pregnancy than some other tests.

Integrated screening uses both first and second trimester tests to predict the risk of having a child with Down syndrome. It is one of the most accurate tests that may be available.⁷ The results are reported only after both sets of tests are finished. This can be cause for concern for women who would like to know test results early on.