Invasive Testing for Birth Defects

Pregnancy is a time filled with wonder, awe, many worries, and almost countless doctors visits. In the course of an uneventful pregnancy, you most likely will only see your doctor once a month; yet if you are in a high risk group or if there are problems detected in the course of the pregnancy, you will find that you might be visiting your physician every two to three weeks. Depending on the nature of the problems anticipated or predicted, your doctor may counsel you to have a number of tests done to determine with close certainty what if any problems there may be found with your unborn child.

Presents Risks

The kinds of tests suggested are plentiful, and by and large everyone will agree to undergo ultrasound imaging and also the maternal blood test; both tests have the ability to detect signs and markers that your child may be affected with a certain potential for having a birth defect. Yet when further testing is suggested, or because of your age implicitly offered, it is important to understand the risks associated with the test and weigh them most carefully against the potential benefits of the procedure.

Chorionic Villus Sampling

Invasive testing discloses birth defects and presents risks to your unborn child. One such test is chorionic villus sampling, which is often abbreviated as CVS. When a birth defect is highly likely, CVS is ordered since the testing may take place during the first trimester, when abortion is still a viable option for the couple, whereas amniocenteses cannot be done until around the fourth month, when abortion in many cases is no longer considered to be a viable option.

During CVS, the substance that is actually sampled is the tissue of the placenta itself. Via a long needle, some cell samples are extracted and sent to a lab for analysis of chromosomal markers indicating the presence of birth defects. Unfortunately, this procedure is somewhat dangerous in that it may introduce an infection into the amniotic sac and thus endanger the health and even the life of the fetus.

Similarly, the possibility exists that some of the amniotic fluid may drain from the sac and affects the lung development of the child. Thus, even though the child will be carried full term, there is a very real risk that because of the underdeveloped lungs the infant may die after birth.


An amniocenteses, on the other had, only samples the actual amniotic fluid and not the placental tissue. Similarly to the CVS, this test also carries the risk factor of infection, yet because the pregnancy is further along by the time this test is indicated, the risk of miscarriage is perceived to be higher than with CVS, even though statistically it is the other way around.

Generally speaking, one in 100 pregnancies will end in miscarriage because of CVS, while one in 200 (some claim it is one in 600) will end in this manner due to an amniocentesis. For this reason it is wise to extensively weigh the risks versus the benefits prior to submitting to these diagnostic tests.