Prenatal genetic testing is not commonly prescribed unless there is an urgent need to detect potential birth defects in a fetus. Because these tests are invasive, there is some risk of infection or miscarriage, although these risks are very low.
Types of Prenatal DNA Testing
A prenatal paternity test is available, but because of the risks of getting the DNA from the baby, a patient should not request these tests unless there is the potential of birth defects or inherited illnesses. Testing simply to determine paternity should wait until birth. If there is a risk of inhereted illness or conditions, a doctor will prescribe genetic testing.
There are two different methods for determining DNA prior to birth: chorionic villi sampling and amniocentesis. Both procedures are invasive and involve puncturing the placenta. Since DNA is set at conception, both tests will provide a DNA test that is admissible in court.
If the mother is 10 to 13 weeks pregnant, chorionic villi sampling may be used to determine DNA. Sometimes the doctor requests this test to screen for other problems, such as Down Syndrome or sickle cell anemia. This test is done by taking cells from the placenta. The OB-GYN can use a catheter inserted through the vagina or a long, hollow needle, which is inserted through the abdomen. The method used depends on the position of the fetus.
If the mother is 14 to 24 weeks pregnant, the OB-GYN can test DNA with amniocentesis. The test uses loose cells that are released into the amniotic fluid. To get a sample of these cells, a long, hollow needle is inserted through the abdomen to collect the fluid. This test may also be recommended if there is a risk for Down Syndrome or Spina Bifida, or if the rH factor of the mother's blood is incompatible with the fetus. An OB-GYN will discuss the risks for both procedures with the mother prior to testing.
When the fetal cells are collected, a buccal swab sample is taken from both the mother and father. DNA testing can take as little as five days, depending on the lab doing the testing. In some cases, doctors may ask for DNA samples from family members as well as the mother and father to assess the potential for inherited conditions.
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