Tests and Diagnosis of Down Syndrome

Down syndrome results due to chromosomal abnormality associated with the 21st chromosome. There are certain tests for down syndrome that a woman must undergo before as well as during pregnancy.
Pre Pregnancy Testing:

  • It is advisable to undergo genetic testing for down syndrome or any other genetic conditions if you happen to have a family history of genetic conditions and abnormalities. However, it is important to note that this testing does not in any way rule out the possibility of the baby being born with trisomy 21.
  • Following this, genetic counseling must be sought by you in order to understand what the test results mean and their implications on you as well as your family.
Pregnancy Screening: Screening during pregnancy includes the following:

  • The doctor may recommend fetal ultrasound and blood tests in the first trimester, also known as combined screening. This ultrasound provides much greater insight into the amount of fluid at the back of the fetus's neck. The thickness of the skin around the neck and its distance from the bones in the neck can also be measured. This is called the skin fold test. However, this test is not widely available due to the fact that this test can only be performed by a specially trained professional. Through the blood test, the mother's levels of human chorionic gonadotropin (hCG) and pregnancy associated plasma protein-A (PAPP-A).
  • There is something called integrated screening that involves tests from the first as well as the second trimester in order to predict the risk of a having a child with down syndrome. This is one of the most accurate tests for determining genetic abnormality risks.
  • Maternal Serum Triple or Quadruple: These tests are conducted in the second trimester. This test checks for three components in the blood namely, Alpha-fetoprotein (AFP), human Chorionic Gonadotropin (hCG) and Estriol (uE3). The test meets the quadruple criteria when a test for Inhibin A is added to the former components. Inhibin A is the protein that is produced by the placenta and the fetus.
Screening for genetic defects is like a double edged sword. This is because some women find it comforting to know what to expect and are therefore better prepared to deal with it whereas some women find it extremely distressing and prefer not to have any warning.

Diagnosis for down syndrome involves diagnostic procedures during pregnancy. Some of them are listed below:

  • Amniocentesis: This procedure is conducted somewhere between the 15th and the 18th week of pregnancy. The amniotic fluid contains the cells of your developing baby. This fluid is extracted and subjected to tests so as to rule out the possibility of any genetic problems. The fluid is extracted by inserting a needle into the abdomen and into the uterus. The results of this test can be obtained in about 2 weeks.
  • Chorionic Villus Sampling (CVS): This test is done before an amniocentesis, around the 12th week of pregnancy. Chorionic Villi are tiny finger shaped growths in the placenta. These contain the genetic make-up of the developing baby. This procedure is conducted by inserting a catheter into the uterus through the mother’s vagina. The results of the same are obtained within a few days.

The important thing to note is that procedures such as these increase the risk of miscarriage and hence these tests are purely choice-based tests and you must not be forced into undergoing any of them. If you feel confused about it, it is advisable to seek genetic counseling.

  • Diagnosis Post-Delivery: The immediately noticeable factors about down syndrome are the physical features of the baby. Doctors will physically examine the baby as well. A blood test conducted on the baby will be able to provide a chromosomal analysis.

Frequently asked questions
  1. Melissa A. Davidson, Primary Care for Children and Adolescents with Down Syndrome, Pediatric Clinics of North America, Volume 55, Issue 5, October 2008, Pages 1099-1111, ISSN 0031-3955, 10.1016/j.pcl.2008.07.001.
  2. Iris Teresa Schapira, Alejandra María Ferrari, Norma Aspres, Ana Belén Guardiol, Ana Inés Antoniutti, Roxana Bedacarratz, Down Syndrome: An Assessment of Infant Psychomotor Development and Its Impact on Social and Familial Integration, International Medical Review on Down Syndrome, Volume 11, Issue 1, March 2007, Pages 2-8, ISSN 2171-9748, 10.1016/S2171-9748(07)70043-0.
  3. D.J. Fidler, Down Syndrome, In: Editors-in-Chief:  Marshall M. Haith and Janette B. Benson, Editor(s)-in-Chief, Encyclopedia of Infant and Early Childhood Development, Academic Press, San Diego, 2008, Pages 422-429, ISBN 9780123708779, 10.1016/B978-012370877-9.00053-0