DNA is contained within nearly every cell of our body, and are the instructions for how everything in our body grows and functions. Our cells are continuously dividing to create new cells. As cells break down, the DNA inside the cell is released into the blood as fragments or pieces of DNA. These DNA fragments present in the blood are known as cell-free DNA.
All pregnant women will have DNA fragments, some that are her DNA and some that is from the placenta. The placenta develops during pregnancy and provides oxygen and nutrients to the developing baby. The placenta usually has the same genetic information as that of the developing baby.
However, in some cases, the genetic makeup of the placenta and that of the fetus (developing baby) are not the same. This can contribute to false positive and false negative results. This is one reason why tests such as cfDNA are considered screening tests; they cannot tell you ‘yes’ or ‘no’ for sure if your pregnancy has any of these conditions. It can only tell you if there is an increased or decreased risk.
When it comes to how the test is run, there are slight differences in the technologies that various labs may use. In general, regardless of the technology used, the lab is looking for differences in the overall amount of chromosome material in mom’s blood.
For example, if the testing finds an increased amount of material that is from chromosome 21, then the test result would say that there is an increased risk that the pregnancy has Down syndrome. Again, the result from a cfDNA test would never be able to tell you ‘yes’ or ‘no’, but can help give you more information about the risk for the conditions tested in your pregnancy.