DNA Testing for Down Syndrome

Present in approximately one in 700 children born in the United States, Down syndrome (also known as Down's syndrome) ranks as the most common genetic learning disorder today. Since the mid 1990s, early detection of the condition has been improving. Recent research has been focused on safer and more accurate testing for Down syndrome.

Identification

• In humans, DNA assembles into 23 pairs of chromosomes. These chromosomes house the genetic information necessary to build our cells, determine the color of our eyes, and everything else making us human. The presence of a third chromosome number 21, Trisomy 21, is the defining characteristic of Down syndrome.

Testing

• Because Down syndrome results from an extra chromosome, a DNA test produces the most conclusive evidence for the presence or absence of this condition. Other blood tests can also be administered to the mother which measure hormone levels.

Considerations

• DNA tests are invasive to the mother, and sometimes to the baby. To obtain fetal DNA, a sample of amniotic fluid will have to be obtained through amniocentesis. This procedure uses a needle to draw fluid from the uterus. According to the Mayo Clinic, there is a one in 200 risk of a miscarriage with this procedure. Risk factors include rupturing the amniotic sac or accidentally injuring the fetus with the needle.

Function

• Once a sample of fetal DNA is obtained, it is sent to a laboratory for testing and the number of chromosomes is analyzed. The chromosome count will determine if the child has Down syndrome.

Alternative

• A fetus's blood enters the mother's bloodstream during pregnancy. Because of this, a blood sample from the mother can be used for DNA testing. This is less invasive and a better choice for the health of the baby.