In the fourth and final episode of the prenatal genetics miniseries, Dr. Fox is joined by Dr. Rebarber to discuss two types of invasive prenatal genetic testing: CVS and amniocentesis tests. Through the episode, they explain why a mother would decide to undergo these tests, what they can detect, how they are performed, and why it’s just not that common for maternal fetal medicine specialists to offer CVS or amniocentesis tests.
“Invasive Testing: CVS and Amniocentesis” – with Dr. Andrei Rebarber
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Dr. Rebarber returns to Healthful Woman to discuss invasive prenatal genetics tests. Invasive testing includes any test that requires a needle to puncture the skin and retrieve genetic material. Dr. Fox also explains the difference between diagnostic testing, which can determine whether a condition is present, and screening, which suggests risk but doesn’t confirm whether conditions are present or not. Invasive testing, including CVS and amniocentesis, are diagnostic tests.
Typically, choosing whether or not to have amniocentesis and CVS tests is up to the patient. Dr. Rebarber explains that a majority of maternal fetal medicine specialists don’t do CVS or amniocentesis tests, because they are generally not in high demand among patients. Dr. Fox adds that the tests are technically challenging, but once trained to perform them it’s not necessarily difficult. Invasive testing is ordered after a carrier screening or other screening test, or simply because a patient wants to be reassured. Dr. Fox says this would be requested by a patient if “they don’t like odds, they just want a yes or a no.”
CVS testing involves sampling from the placenta either trans-vaginally (using a catheter placed through the cervix rather than a needle) or transabdominally (using a needle through the abdomen). Dr. Rebarber explains that the placenta cells generally have the same genetics as the baby, so sampling them can tell you about the baby’s DNA. Amniocentesis tests are performed to collect amniotic fluid, and are always transabdominal. Both types of tests are done using ultrasound, so the physician can see everything as they perform the test. Dr. Rebarber explains that while he would make his best effort not to touch the baby, there is little danger if they are touched by the needle. However, there is some danger in hitting the umbilical cord, so avoiding this is his priority. Dr. Rebarber comments that studies are now showing that though there are some risks, amniocentesis tests are even safer than once thought.
Drs. Fox and Rebarber also discuss how amniocentesis tests were performed in the past, when virtually all mothers over 35 were encouraged to have the test, as the risk of having a child with Down syndrome and the risks of the test were assumed to be virtually the same. Now, genetic testing is offered as an option to all patients, though it’s not a requirement.
Dr. Andrei Rebarber is a board-certified OB/GYN with subspecialty certification in maternal fetal medicine and founder and President of Maternal Fetal Medicine Associates, PLLC, and Carnegie Imagine for Women, PLLC. Dr. Rebarber specializes in fetal diagnostic procedures, recurrent pregnancy loss, 2D and 3D ultrasound, and gynecologic sonography. A Clinical Professor at the Ichan school of Medicine, Dr. Rebarber has authored several book chapters and 140+ peer-reviewed publications and is considered one of the leading physicians in his field.