Screening for Birth Defects

By: Bradley G. Goldberg, M.D.

Statistics indicate that between 3-4% of all newborns will be affected by some type of birth defect. Some may be mild, others may be severe. Some of these defects may not even be noticed until several years after birth.

The good news is that the vast majority of babies are born normal. While most birth defects cannot be detected before delivery, modern medicine is able to screen for several different types of defects and that number should increase as research continues.

Before a woman becomes pregnant, doctors can use blood tests to screen for several different birth defects. This includes cystic fibrosis, sickle cell anemia, tay sachs disease, and several other genetic disorders as well.

After a woman discovers that she is pregnant, most of these same tests can still be performed. In addition, blood work done during pregnancy can detect most cases of Down’s syndrome, neural tube defects (such as spina bifida), and trisomies 18 and 13. Ultrasound studies during pregnancy can potentially screen for major defects of the fetal digestive and urinary tracts, as well as problems with defects of the face, brain and extremities.

An important point to remember is that these are screening tests. Screening tests are intended to identify persons at risk for a particular problem, not to actually make a definitive diagnosis. Diagnostic tests give the final answer as to whether or not the condition identified in the screening test is actually present.

For example, if a person has a positive screening test for Down’s syndrome this means that there is a risk of Down’s syndrome, although the baby may be completely normal. The next step is to perform a diagnostic test, which in this example would be an amniocentesis. This diagnostic test will give the final answer of whether or not the baby is affected.

Scientists have recently finished mapping the 80,000 genes of the human body. As a result, there will likely be several new screening tests for various genetic conditions emerging over the next several years. One of the newest is a screening test for Cystic Fibrosis which should be considered by all couples, but especially Caucasians.

In summary, several screening tests for birth defects now exist and some can be performed before a woman is pregnant. These tests are not perfect, and they are constantly being improved. A positive screening test does not mean that there is a definite problem; it means that a diagnostic test must be performed in order to make the final assessment.

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