Chorionic villus sampling (CVS) and amniocentesis are diagnostic tests that determine whether genetic abnormalities are present in a fetus. Both types of prenatal genetic testing are designed to be performed prenatally, or before the baby is born. These procedures detect genetic abnormalities in the fetus and can provide you with critical information regarding treatment options and help you determine if your child will need special care or treatment once they are born.
What Is Chorionic Villus Sampling?
CVS is a procedure that uses a needle or catheter to obtain a biopsy of cells from fingerlike projections (villi) of the fetus’ portion of the placenta (chorion). This sample is obtained by inserting the needle in a transcervical or transabdominal manner—either through the cervix or through the abdomen itself. Because chorionic villi are projections from the placenta, they share the same genetic information as the fetus. Therefore, this sampling can be tested for genetic abnormalities without the need to take a cell sample from the fetus itself.
What Is Amniocentesis?
Amniocentesis tests the amniotic fluid of a pregnant woman for fetal genetic abnormalities. Amniotic fluid is fluid that surrounds the fetus during pregnancy, acting as a buffer against the outside world. It is useful for genetic testing because it contains fetal cells, which contain DNA and information about the fetus’ genetic makeup. Like CVS, the primary reason to perform amniocentesis is for genetic testing.
What Is the Difference Between CVS and Amniocentesis?
Aside from the source of the fetal cells, the primary difference between CVS and amniocentesis is the timing of the procedure. Physicians can perform CVS as early as 10 weeks of pregnancy, although it usually occurs between 11 and 14 weeks. When amniocentesis occurs for the purpose of genetic testing, physicians often recommend administration between weeks 15 and 20 of pregnancy.
Because it is done earlier than amniocentesis, CVS can reveal genetic risks earlier in the pregnancy. There are, however, some drawbacks to CVS. It cannot detect defects in a fetus’ brain or spinal column. Furthermore, it cannot detect Rh incompatibility, which is a condition that occurs when a particular surface protein is present in either the mother or fetus and absent in the other, causing potential issues during birth. Conversely, amniocentesis can detect spinal column defects, Rh incompatibility, and other birth defects CVS can miss.
Common Reasons for Chorionic Villus Sampling and Amniocentesis
While an informed pregnancy is important for every individual, physicians strongly recommend prenatal genetic testing for certain women. Some common reasons women opt to get CVS or amniocentesis include:
- Being 35 or older, which increases the risk of having children with chromosomal conditions like trisomy 21 and trisomy 18.
- Having spinal column or brain defects.
- Having a family history of genetic conditions.
- Having given birth to other children with genetic conditions.
- Testing earlier in the pregnancy that returned abnormal results.
What Is Right for Me?
CVS can reveal the results of genetic testing earlier in the pregnancy and may be a good fit for many pregnant women. However, if you have a child with brain or spinal defects, have neural tube disorders yourself, or have had abnormal test results earlier in the pregnancy, amniocentesis may be a better choice for you. You should discuss your options with your care team to determine which procedure best fits your situation.
Prenatal genetic testing is a low-risk tool that can reveal critical information about the health of your fetus. With this knowledge in hand, you can begin to make informed decisions as you prepare for your future child.
Sources: https://www.cdc.gov/mmwr/preview/mmwrhtml/00038393.htm#:~:text=CVS%20utilizes%20either%20a%20catheter,surrounds%20the%20fetus%20is%20removed https://www.mayoclinic.org/tests-procedures/chorionic-villus-sampling/about/pac-20393533 https://www.mayoclinic.org/tests-procedures/amniocentesis/about/pac-20392914