The subject of prenatal testing is one that sparks a lot of debate in the Down Syndrome community. Prenatal testing is used for a variety of reasons.
One reason that parents want to test their fetus is so that they will have time to prepare for a child that has a disability. Due to potential complications with the birth of a child with disability, the parents may want to prepare special arrangements.
The second reason is to set up a plan for adoption of the baby. While the parents may not be willing to abort the fetus, monetary or economic reasons may prevent them from caring for the child.
The third reason is to use these tests to determine whether or not they want to continue the pregnancy. A lot of the reasoning behind terminating the pregnancy is based off of fear or misunderstanding of Down Syndrome. Also, parents may not feel ready for a child with disability.
There have been many improvements to the types of prenatal testing over the years. It is important to note that these tests are not 100% accurate 100% of the time. It is possible to receive false positives and false negatives. New tests are becoming available which are more accurate are safer for both the mother and the fetus.
There are two main types of tests available: screening and diagnostic testing. Screening tests are used to determine the risk of the fetus having Down Syndrome. Diagnostic tests are used to determine a positive result. A better way to describe this is that screening tests show you if it's possible that your child will have Down Syndrome while diagnostic tests tell you 'yes your child does have Down Syndrome.'
Your decision about prenatal testing should be discussed thoroughly with your physician and your partner. Down Syndrome is not a stable disability and your decision should not be based on the generic stereotypes. Although health problems can be prevalent, the life expectancy has increased dramatically in recent years and the learning potential of those with Down Syndrome has increased. The improvement of learning potential is due to an increased of a loving home environment and an increase of stimulation and learning opportunities. There are also more programs and government provided services that help those with Down Syndrome live more independently.
Diagnostic Tests
Invasive Prenatal Tests
The only reliable way to test for Down Syndrome is to perform a diagnostic test, which is an invasive procedure. There are two main tests which are used: amniocentesis and chorionic villus sampling (CVS).
Amniocentesis can be performed after 15 weeks. The test is executed by removing some of the amniotic fluid and analyzing the chromosomes.
CVS is performed between weeks 11 and 14. This test is executed by removing some tissue from the placenta to be analyzed.
There is a third test which is available, but not commonly used. It is the Percutaneous Umbilical Blood Sampling (PUBS) which is performed after 20 weeks. Similar to amniocentesis, this test is executed by removing blood from the umbilical cord to be analyzed. This test is only performed for women who have a high risk of having a child with Down Syndrome as there is a significant risk for the mother and fetus.
Since these tests are invasive, there is a small chance of miscarriage. Before making a decision on either prenatal testing or ending a pregnancy, the parents should become well informed about all the risks.
Below is a video (1 hour 15 minutes) which explains all forms of prenatal testing for Down Syndrome and the associated risks. There is also a discussion of new testing which is becoming available for women.
Down Syndrome Guild of Greater Kansas City Informed Consent and Prenatal Testing Presentation Featuring Brian Skotko, MD, Patricia E. Bauer, Journalist, Mark W. Leach, J.D. and Diane Plantz, MD, MA. and Dr. John Yeast as moderator
Screening Tests
Non-Invasive Testing
Screening tests are non-invasive, which makes them safer for the fetus and the mother. Historically, these tests were only given to women over the age of 35. This was because these were the women who were at the most risk for having a child with Down Syndrome. These tests are not conclusive, as they only show the potential for the risk, not a definitive "yes" or "no."
Some of most popular screening tests include the first trimester screen, the triple screen, and the quadruple screen.
The earliest test that women can use to detect the risk of Down Syndrome is the first trimester screen. This test is performed by extracting a blood sample and using an ultrasound. The blood test is used to measure specific pregnancy hormones hCG and PAPP-A. The ultrasound portion is used to measure nuchal translucency, which is the fluid beneath the skin behind the baby's neck. An abnormally high or low amount of the two hormones and increased amount of fluid are both signs that the baby may be at risk of having Down Syndrome. This is not a qualitative test; your physician will only tell you whether your results are abnormal and whether there is a high risk.
The triple screen test is a test that is performed in the second trimester. This test is a blood screening test that measures three substances: AFP (a protein produced by the fetus), hCG (a hormone), and Estriol (estrogen produced by the fetus and the placenta). There is very little risk to the mother or fetus during the test. This test, however, is known to have a high occurrence of false positive results.
Another second trimester screen test that is performed is the quadruple screen. This test is exactly like the triple screen test, with the exception that it is looking at one more substance: inhibin-A (a protein produced by the placenta and ovaries). The false positive results for this test are much lower than the triple screen test and the likelihood of determining risk is higher.