Invasive Testing
What are my Invasive Testing options?
There are two invasive testing options available during pregnancy: chorionic villus sampling (CVS) and amniocentesis. These are considered diagnostic, meaning most of the time they can provide a ‘yes’ or ‘no’ answer about whether a pregnancy has a chromosome or other genetic condition. These testing options are much more comprehensive than blood/screening tests, but they do involve a level of risk.
Chorionic Villus Sampling (CVS)
Chorionic villus sampling (CVS) is typically performed between 11 and 14 weeks of pregnancy. During CVS, a small amount of placental tissue is collected for testing. CVS is performed transcervically or transabdominally, with the maternal fetal medicine specialist (MFM) using ultrasound as a guide. Whether the MFM decides to perform a CVS transcervically or transabdominally depends on the location of the placenta. The entire procedure typically takes a couple minutes to complete.
- The transcervical method involves passing a thin tube through the opening of the cervix and into the placenta.
- The transabdominal method involves passing a thin needle through the patient’s abdomen and uterus into the placenta.
The genetic information found in the placenta is usually identical to that of the baby. However, in a small number of cases, the baby’s genetic information is different from that of the placenta and further testing such as amniocentesis may be recommended to clarify CVS results.
Amniocentesis
Amniocentesis is typically performed after 16 weeks of pregnancy. Using ultrasound as a guide, a thin needle is inserted through the pregnant patient’s abdomen into the amniotic sac, a fluid-filled area surrounding the baby. A small amount of the amniotic fluid is collected for testing. The fluid contains some of the baby’s cells, which contain the baby’s genetic information.
What does Invasive Testing test for?
The results of invasive testing are diagnostic, meaning that the results are definitive for the conditions tested.
There are various genetic tests that can be done through diagnostic testing. Some of the most common conditions tested include Down syndrome, trisomy 13, trisomy 18, and differences in the number of X and Y chromosomes. Genetic testing for specific conditions can also be done when there is a known genetic condition running in the family or if an abnormal ultrasound finding is seen. It is not possible to test for all genetic conditions or birth defects.
What are the risks?
CVS and amniocentesis procedures are performed at a doctor’s office by a MFM specialist. Most patients who have an invasive test do not have a complication and can return to their normal activities within 1 to 2 days after the procedure. The risk for complications includes cramping, infection, leakage of amniotic fluid, and premature labor or miscarriage. This risk is expected to be less than 1%. Patients may also experience some discomfort during the procedures, including the sensation of cramping, pressure, or pinching.
Is this testing right for me?
Making the decision of whether or not to proceed with genetic testing can be difficult. Decisions around genetic testing and the type of testing, invasive or non-invasive, should be based on each patient’s specific needs, values, personality, and beliefs. It is important to discuss these and any questions you may have with your doctor or genetic counselor.
Where can I learn more about invasive testing?
You can visit these helpful websites or call 713-486-9302 to schedule an appointment with a genetic counselor to discuss diagnostic testing.