Types of Prenatal Genetic Screenings and Diagnostic Tests
A blood test is available to women to provide screening for some disorders. Screening tests alone are not diagnostic. If a blood test finds a possible problem, a prenatal diagnostic test may be recommended to confirm a diagnosis. These diagnostic tests include chorionic villus sampling (CVS) or amniocentesis and are used to perform fetal chromosome analysis or microarray analysis of fetal cells.
Chorionic Villus Sampling (CVS)
Chorionic villus sampling (CVS) is a diagnostic test usually performed between the 10th to 12th weeks of pregnancy. The perinatologist gently suctions a small piece of the placenta on the outside of the fetal sac to obtain fetal tissue and cells in order to look at fetal chromosomes and/or DNA, and potentially other genetic conditions in the fetus.
A genetic amniocentesis is a diagnostic test usually performed between weeks 16 to 20 of a woman’s pregnancy. The perinatologist inserts a hollow needle to remove a small amount of amniotic fluid from around the developing fetus. This fluid has fetal cells floating in it that allow the laboratory to study fetal chromosomes by routine analysis or by microarray, as well as to obtain fetal DNA for other types of genetic testing depending on the family history. This fluid also allows testing for neural tube defects (spina bifida) or abdominal wall defects (gastroschisis, omphalocele) in the developing fetus.
There is another form of amniocentesis that is not genetic, but rather performed when there’s a risk of premature birth, to check if a baby’s lungs have matured; this is not a genetic test.
A Word of Caution
Although advances in genetic testing have improved doctors’ ability to diagnose and treat certain illnesses, there are still some limits. Genetic tests can identify a particular problem in a chromosome or gene, but can’t always predict how severely a person who has the condition will be affected, as all of us are unique. We will do everything we can to help provide the support and information you need, with the understanding that there may be some things we won’t know until your baby is born.