Question

Pregnancy, Fertility and Childbirth

Which screening tests are performed during pregnancy?

A Answers (2)

  • AMichael Roizen, MD, Internal Medicine, answered
    Screening tests are not designed to diagnose a genetic syndrome, but rather to provide a more accurate risk estimate for certain conditions, such as Down syndrome. There's no test available during pregnancy that will rule out all possible genetic diseases and guarantee a healthy baby. If you have any concerns regarding diseases that run in your family, it may be worthwhile to meet with a genetic counselor to discuss the risks for your baby and appropriate testing options during pregnancy.

    Common screening tests include:
    1. First trimester screening (typically consisting of blood work and an ultrasound to measure the thickness of the skin at the back of the neck, (called nuchal translucency) which indicates if there's a risk that the fetus has Down syndrome)
    2. Maternal serum screening, sometimes called a quadruple check, which is performed in the second trimester
    3. Combined test using components of the first two
    4. Screening for a group of common birth defects, called open neural tube defects, can be performed between 15 and 20 weeks by measuring a chemical in the mother's blood
    5. A comprehensive ultrasound evaluation in the second trimester (typically performed between 18 and 20 weeks) evaluates growth, screens for birth defects and looks for any physical markers suggestive of a chromosomal abnormality.
  • The most common screening test performed during pregnancy is ultrasound, which produces an image known as a sonogram. This procedure has many uses, including screening the fetus for physical malformations. In addition to ultrasound, a number of screening tests for Down syndrome and other characteristics of your developing baby are available.

    Most screening tests give an estimate of the likelihood that a certain condition is present in the fetus. For example, the likelihood of a fetus having Down syndrome may be stated as 1:150, meaning that there is one chance in one hundred fifty that the fetus is affected. (This is based on the rate at which the condition occurred among babies of women who had similar test results and who shared the same age, ethnic background, smoking status, and other characteristics.) Since screening tests are designed to identify as many potential cases as possible, they sometimes suggest that a condition is likely to be present when in fact it is not present. This outcome is called a "false positive" result. Screening tests allow many false positives because that ensures that almost all true positives will also be caught. For this reason, if a screening test is positive and you want to determine whether the condition is really present or not, you will need diagnostic testing.

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