Antenatal Genetic Testing
When it comes to genetic testing there are many conditions to test for, depending upon personal or family medical history, ancestry, and more. But most often genetic testing looks for Down Syndrome, a condition marked by problems with intellectual and physical development, as well as the potential for specific birth defects. Down Syndrome is genetic, caused by a gene problem, but it is not passed down from generation to generation, like height or chance of getting certain cancers.
Genetic testing is different than regular prenatal care? There are certain conditions that go undetected with the regular pregnancy tests. These medical problems are only found and diagnosed after birth. It makes sense to do MORE testing, so as not to miss anything.
There is an important question to ask when considering which extra or additional prenatal tests to do: How will this test result change the prenatal care, and how is that better for the developing baby?
Focusing on Down Syndrome, we can ask specifically, how is prenatal care different if we know the baby has Down Syndrome. The answer, for pregnancies with a normal 20 week ultrasound, is “it’s not.” Prenatal care for ultrasound-normal babies with and without Down Syndrome is the same. So is labor. And so is delivery. Down Syndrome does not change how we manage an otherwise normal pregnancy.
So What is Different?
There are certain birth defects, especially of the heart and stomach and spine, which DO IMPACT what is done for prenatal care and delivery. Testing for Down Syndrome is VERY IMPORTANT in pregnancies with birth defects found on ultrasound. Medically important birth defects can be detected by ultrasound at 20 weeks; a test we get in all pregnancies. In the old days there was a difference between a regular ultrasound and a genetic ultrasound, formerly called Level ONE and Level TWO. Now, ALL ultrasounds are the equivalent of Level Two.
If the diagnosis of Down Syndrome does not change how we manage pregnancy, why do it?
One reason to test for Down Syndrome is “to make sure everything is fine.” A negative test can be reassuring. Also, some women or couples may consider pregnancy termination based on the sure diagnosis of Down Syndrome. Also, Down Syndrome testing became a habit in women over 35 yrs. Old habits are hard to break, even when it comes to medical care. After age 35, the chance of Down Syndrome in pregnancy is the same as the chance of a miscarriage complication from one of the old Down Syndrome tests. Today, we know more about age and pregnancy, and we have more, more reliable, and less risky tests. Age 35 is no longer a reasonable or reliable measure for considering this type of testing.
Genetic Testing Timeline
|10-12||Chorionic villus sampling (CVS) is a prenatal test that diagnoses chromosomal abnormalities such as Down syndrome, as well as a host of other genetic disorders.|
Non-Invasive Prenatal Testing (NIPT) analyzes cell-free fetal DNA circulating in maternal blood
|11-14||Nuchal Fold Ultrasound, with blood testing|
|15-22||Quad Screen (serum screening)|
|19+||Ultrasound for anatomy|