What is Prenatal DNA Testing?

Prenatal DNA testing is an examination done before birth to determine the paternity of a child. This is accomplished by comparing the unborn baby’s deoxyribonucleic acid (DNA) to the possible father’s DNA. The mother will have to undergo a medical procedure for the doctor to collect the unborn baby’s DNA, while the possible father can generally give his DNA through a cheek swab.

There are two types of prenatal DNA testing procedures: invasive and non-invasive. Invasive procedures present some risks to the fetus. Despite the risks, since invasive procedures can be as accurate as a standard, or postnatal, paternity test, they are more widely used than a prenatal non-invasive procedure. To avoid the risks invasive procedures pose but to get more accurate results than those that might be provided by a prenatal non-invasive procedure, a mother might want to opt for a standard paternity test.

Amniocentesis is one of two invasive prenatal DNA testing procedures. The doctor uses ultrasound as a guide in retrieving fetal cells from the amniotic fluid surrounding the fetus. A needle is inserted through the mother’s abdomen and into the uterus in order to collect the cells. These fetal cells contain the unborn child’s DNA, which can then be used for the test. This procedure is generally done between the 14th and 21st weeks of pregnancy.

Chorionic villi sampling (CVS) is the other invasive prenatal DNA testing procedure. Again, the doctor uses ultrasound as a guide. A needle or catheter is inserted through the mother’s abdomen or cervix to collect cells from the placenta, or the membrane, surrounding the fetus. This procedure is generally performed earlier than amniocentesis, between the 10th and 13th weeks of pregnancy.

Both amniocentesis and CVS pose risks such as bleeding, infection or miscarriage. In amniocentesis, the risk of miscarriage is lower than that of CVS. The chances of a miscarriage associated with amniocentesis are between 0.25 and 0.5 percent. A miscarriage associated with CVS carries a 2-percent risk. If CVS is performed before the ninth week of pregnancy, it might cause the infant to have defects in the fingers or toes.

The non-invasive prenatal DNA testing procedure requires separating fetal DNA from the mother’s blood. This is possible because during pregnancy, fetal DNA can enter and be found in the mother’s blood. There are some concerns with this procedure, though, the first being that the mother’s blood can contain DNA from pregnancies for over 20 years, so previous fetal DNA still exists in the bloodstream. Second, a sufficient amount of fetal DNA in the blood is lacking. Third, this non-invasive prenatal DNA testing procedure results in only 70-percent accuracy.