When most of us hear CVS, we think of the store—shampoo, cotton swabs, bandages, vitamins. We rarely ever think of first-trimester genetic testing, unless you are an obstetrician! But CVS goes way further than your local drugstore and stands for more than Consumer Value Stores. In the land of OB, it means Chorionic Villus Sampling, and the information we get out of it is way more valuable than any Super Savings discount your local CVS has ever offered.
CVS and amniocentesis (a.k.a. amnio) comprise what we traditionally call invasive diagnostic genetic testing. They get answers that are highly accurate and therefore shed a lot of light about your little one’s chromosomes and genetics. Whereas in the past we only offered it to women based on their age (older than 35) or their risk factors, nowadays anyone who wants invasive diagnostic testing can have it. You just have to know about it and ask for it. And while prenatal genetic screening (what we can test for) has “come a long way, baby,” the options for diagnostic tests (a.k.a. how to get the cells to get the information) have remained the same. Let us give you the lowdown.
However, before we can delve deep into the depths of CVS and amnio, it’s important to clear up two key concepts:
- A screening vs. a diagnostic test
Simply stated, a screening test is used to check for the possibility of a disease. Most of us get several of these a year (think Pap Smears, mammograms, colonoscopies) depending on our age. In most cases, the screening test is the end of the rope—see you next year! It is only when the screening test is positive and suggests that something is up that we need to move on to the bigger guns, otherwise known as the diagnostic test. A diagnostic test confirms if what was seen on the screening test is really there.Bringing this back to prenatal testing, screening tests include both blood tests (PAPP-A, hCG) and an ultrasound (nuchal translucency) that is usually done at about 11 to 13 weeks. When these look off, it’s a good idea to move on to more definitive and accurate tests. Cue the invasive tests.
- A non-invasive vs. an invasive test
This one is probably a bit more straightforward but still needs some explanation. While a non-invasive test may require a blood draw or an ultrasound, the pregnancy itself (a.k.a. the amniotic sac, the chorion, or the placenta) is not being disturbed. An invasive test will break more than your skin. It will require that a needle be passed either through the vagina or the abdomen to obtain tissue. Given the more involved nature of the invasive test, it carries greater risk. However, it also carries greater reward; that is, it is accurate 99% of the time. Accuracy is key when couples and individuals are making difficult decisions
Now that we cleared that issue up, we can get down to the nitty gritty of CVS and amnio: when they are done, how they are done, and what you can expect. So if your screening test came back abnormal, e.g., an elevated risk for chromosomal abnormalities or if you chose to skip screening and go right to diagnostic—which some women do, it’s your choice!—you have two options…
- The cells (a.k.a. information on the genetics) are obtained from the placenta.
- We can get these cells in one of two ways: either by passing a needle through the abdomen or the vagina. The approach varies based on physician preference and skill.
- The test is usually performed between 10 and 13 weeks.
- The results are not only super speedy (the cells are processed quicker after a CVS than an amnio) but also the test is performed early in the pregnancy.
- There are risks. And just like any procedure, the risks must be weighed against the benefits. In terms of CVS, our no. 1 concern (and yours truly, too) is fetal loss. Good news is that the numbers are reassuring, and the risk of loss following the procedure is very low (1 in 455).
- The cells are obtained from the amniotic sac (the fluid that surrounds the fetus).
- We can get these cells one way and one way only—by passing a needle through the abdomen.
- The test is usually performed between 15 and 20 weeks but can also be done later in certain situations.
- The results are more like snail mail than email. It takes the lab about 7 to 14 days to come up with a final answer (CVS takes about 5 to 7 days). Additionally, it is done later in the pregnancy.
- There are risks here, too. But here the risk of fetal loss is somewhat lower at about 1 in 800.
Admittedly, we just barely scratched the surface of prenatal genetic testing (#weLOVEtheTRUTH). The specifics of what can be tested for, in what lab, and what it really means goes way, way deeper. However, in most cases you don’t even need to walk past the shallow end to get what’s going on. But before you take the plunge into the CVS or amnio pool, make sure you have lifeguards on deck (a.k.a. a genetics counselor and your OB). Even the “best swimmers” can get lost, confused, and overwhelmed without someone watching over them.
Just as you wouldn’t swim in rough waters alone, don’t venture into invasive diagnostic testing without a guide. This stuff can get complicated quickly. No matter where you swim, safety always comes first!