Prenatal genetic testing is one of the first big pregnancy decisions that you will make. With most tests being offered at the end of the first trimester or beginning of the second, your doctor will most likely be informing you about your options pretty early on in the process. My doctor gave me a sheet with all of my options, asking me to choose which one (if any) I wanted at my very first in-depth prenatal appointment. So, preparing yourself as to your options is very important.
Types of Prenatal Genetic Testing
While there are different options within these types, the two main ways to understand your baby’s genetics is through screening tests and diagnostic tests.
- Screening tests are no-risk screens that often involve taking blood or ultrasounds that can determine your risk for genetic disorders.
- Diagnostic tests, on the other hand, tell you whether or not your child actually has a genetic disorder. These tests are much more invasive and do carry certain risks with them.
Prenatal screenings are often the first, and most common, type of genetic testing offered to pregnant women. Even if you are low risk, have no history of genetic disorders and have been tested yourself, your doctor is still likely to recommend these screenings as part of your prenatal care. All of the different tests use a blood sample and/or an ultrasound to determine your risk. It’s important to note that these tests can not determine whether or not your baby actually has any disorders, but if the results come back with a high risk, you have the option to do more intensive diagnostic testing.
Noninvasive Prenatal Test (NIPT)
As your baby forms, its’ DNA will enter your bloodstream. The NIPT test locates that DNA through a blood sample and looks for abnormalities. The NIPT is done between weeks 11 and 13 and tests for three main genetic disorders, including Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), and Trisomy 13 (Patu syndrome). In addition to testing for genetic disorders, this test will also tell you the gender and blood type of your baby. If the results come back positive for any of the disorders, your doctor will likely suggest a diagnostic test. Either way, you will probably also receive an additional screening, such as an NT test, to confirm the risk.
Nuchal Translucency Screening Test (NT)
This screening test is also done between weeks 11 and 13 of the pregnancy. Instead of looking at your blood, it looks at the baby, specifically the baby’s neck. If a fetus has a higher than normal amount of fluid at the base of their necks at this stage, it is often a sign of a chromosomal problem. This test measures your baby’s length and the thickness of the neck via ultrasound. A technician will take these measurements, along with your age and the gestational age of the baby, to determine the risk factor. This test, along with the results form a NIPT, can help you understand whether or not you need further testing.
Level 2 Ultrasound
This screening test is usually done at around 20 weeks. It is often less daunting than the previous tests as you likely already know your risk of genetic disorders and abnormalities. This test uses an ultrasound to make sure your pregnancy is developing normally. This test is often a parent’s first glimpse at what their baby will look like.
After receiving the results of the above screening tests, some women may never have to think about the diagnostic tests. But, for many women, a positive result on a screening can lead to more testing to determine if the abnormality is actually there. Women who have a family history or know they are a carrier of a genetic disorder will often skip straight to these tests instead of first undergoing screening tests. Instead of looking to the mothers’ blood or measuring the baby via ultrasound, diagnostic tests go straight to the baby, using his or her genetic material to understand whether or not an abnormality exists.
Chorionic Villus Sampling (CVS)
A CVS is a test that is done during your first trimester, specifically between weeks 10 and 13. It takes a tissue sample from the placenta to analyze the genetics of the baby and determine whether or not the DNA shows any chromosomal abnormalities. During the procedure, a CVS specialist or your doctor will use an ultrasound machine to determine where to collect cells. The doctor inserts a thin needle either in the abdomen or the sample may be taken from the vagina or cervix via a tube. While the entire procedure usually takes about 30 minutes, most women say they experience some sort of discomfort during it. The test is 98% accurate and the risks are low, but bleeding and cramping may occur.
This test is done a bit later in the pregnancy, usually around weeks 16 to 18, but it can be performed as late as 20 weeks. This test is similar to the CVS as your doctor will use an ultrasound to locate the amniotic sac. He will insert a thin needle into the abdomen and uterus to collect fluid. An amniocentesis checks for hundreds of genetic disorders and is 99% accurate. However, it can not determine all genetic problems, nor can it tell you how severe a problem is. Side effects are small, but you will likely be told to rest for a few hours, and avoid sex, heavy lifting, and extreme exercise for a few days. While the risks are extremely low, there is an estimated one in 300-500 chance of the procedure ending in a miscarriage.
Prenatal genetic testing can be a nerve-wracking part of every pregnancy. Knowing your options and your risks is a great way to ease some of those nerves during your pregnancy. Talk to your doctor as soon as possible about all of your options and what they recommend for you specifically. Know, however, that the choice is yours as to what, if any, tests you choose to have done.