Chorionic villus sampling or CVS is a diagnostic test administered in early pregnancy that can determine whether a fetus possesses certain conditions. Typically, these conditions are chromosomal or genetic, such as Down syndrome or cystic fibrosis. Physicians perform the test by sampling a small bit of tissue from the placenta. Though CVS is an effective way to learn about a baby’s health, there are several risks. In addition, there are two methods for physicians to perform the test: transcervical or transabdominal.
The placenta is a temporary organ that connects a developing fetus to its mother’s uterine wall via the umbilical cord. This allows for a number of important functions, including nutrient uptake, gas exchange, waste elimination, and temperature regulation. The chorionic villi are small, wispy projections of tissue that share the fetus’ genetic makeup. In chorionic villus sampling, physicians take a small sample from the chorionic villi and test for any abnormalities. Though most people associate CVS with testing for Down syndrome, the test can detect more than 200 different disorders.
There are a variety of reasons that a physician would choose to do CVS. Typically, medical experts perform the test between the 11th and 14th week of pregnancy. This is because the test results may affect how physicians and the mother will manage the pregnancy. Primarily, physicians perform the test following abnormal ultrasounds or cell-free DNA tests. Mothers who have had previous pregnancies with chromosomal conditions may require CVS to determine if the current pregnancy also possesses any issues. Doctors also tend to test women over the age of 35, as their pregnancies have a higher risk of chromosomal conditions.
Though chorionic villus sampling is an effective testing procedure, there are some reasons why mothers and physicians avoid it. The test is not capable of detecting congenital disabilities such as neural tube defects. Some women may have conditions that limit what type of CVS doctors can use. For example, physicians may choose not to use transcervical CVS if a woman has a genital infection such as herpes. Additionally, a woman’s placenta may not be accessible for any number of reasons.
Generally, CVS is a fairly safe testing method. However, it does carry several risks. The primary risk is Rh sensitization. The sampling process may cause some of the fetus’ blood to enter the mother’s bloodstream. If the fetus’ blood is Rh-positive while the mother’s blood is Rh-negative, the mother’s body will begin to create antibodies to protect against the Rh-positive blood. This can potentially harm the fetus. If this is a concern, doctors will use Rh immune globulin to prevent the mother’s body from creating the antibodies.
Though rare, other issues may result from chorionic villus sampling. Some women may experience miscarriages following the procedure. While some sources state that the risk is as high as two percent, recent studies find that the risk of a miscarriage that directly results from CVS is as low as 0.22 percent. Older studies suggest that CVS can lead to defects of a baby's fingers and toes. However, modern research suggests that this only occurs if the procedure takes place prior to the tenth week of pregnancy. Though uncommon, there are reports of some women developing uterine infections following CVS.
Prior to the test, a doctor will inform their patient of the risks and steps of the procedure. Often, this includes signing a consent form. Depending on the location of the uterus and placenta, physicians may ask some women to have a full bladder before the test. This can help move the uterus to a more accessible position. The test begins with the patient lying down on an exam table with their hands behind their head. A technician will perform an ultrasound. Then, depending on the location of the placenta, the doctor will perform the test, entering either through the cervix or through the abdominal wall.
If the doctor chooses to perform a transcervical chorionic villus sampling procedure, they will begin by inserting a speculum into the vagina. This allows them to properly observe the cervix. Then, they will use an antiseptic solution to clean the vagina and cervix. The ultrasound will provide the doctor with guidance as they insert a thin tube through the cervix toward the chorionic villi. They will gently suction cells from the chorionic villi through the tube into a syringe. The doctor will then remove the tube and speculum to conclude the procedure.
Some women's uteruses are in a position that makes transcervical CVS procedures more dangerous. In this instance, physicians carry out transabdominal CVS. This is a slightly more complex operation than transcervical CVS. To begin, a health care provider will cleanse the abdomen with an antiseptic. Some women may receive a local anesthetic to help them with the pain. The procedure begins when the doctor inserts a small needle into the abdomen. The ultrasound will allow the doctor to guide the needle through the abdomen, into the uterus, and into the placenta. The physician will then gently suction cells into the syringe. After removing the syringe, they may cover the area with an adhesive bandage.
Many women who hear about the steps of the procedure worry about how CVS feels. The ultrasound doesn’t hurt. Some women may experience minor discomfort if their physician also uses slight pressure to find the position of the uterus. Some women state that the transcervical method feels similar to a Pap test. This may involve discomfort, a feeling of pressure, possible cramping, and light vaginal bleeding. The transabdominal method may cause a stinging sensation if physicians opt to not use a local anesthetic. Additionally, many women feel cramps as the needle enters their uterus.
Doctors will monitor both the mother and fetus for the weeks following the procedure. It can take some time for the results of the test to return from the genetics lab. Health care providers recommend at least 24 hours of rest following chorionic villus sampling and may suggest abstaining from sexual intercourse for several weeks. They will also ensure there are no issues following the procedure, such as bleeding, fluid leakage, or fevers. If the results of the procedure show a chromosomal or genetic condition in the fetus, doctors will work with the parents to determine a suitable path for the pregnancy.
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