There are different kinds of prenatal tests conducted in the course of pregnancy to collect information regarding the health of the mother and fetus. These prenatal tests help to detect the birth defects and health issues regarding the fetus. Prenatal tests include blood tests, ultrasound, urine tests, pap smear, and so on. While some of these tests are a part of routine pregnancy procedures, others are performed if the mother or the child has a potential risk of developing certain health issues. This article talks about one such prenatal test – chorionic villus sampling.
What Is Chorionic Villus?
Chorion is a membrane that develops in the course of pregnancy. It is through this membrane the mother connected with the fetus. The chorionic villi, as the name indicates, are small villus or finger-like projection that appears in chorion to increase the contact area with the mother’s blood. The importance of the chorionic villi in pregnancy is that the genetic material in chorionic villus cells and fetal cells are the same. This is because both are developed from the fertile egg.
What Is Chorionic Villus Sampling (CVS)?
Chorionic villus sampling (CVS) is a prenatal test performed for detecting chromosomal abnormalities and other inherited disorders and birth defects. In this test, a sample of chorionic villi is removed from the placenta and sent to the lab for genetic analyzing and detecting abnormalities.
What Kind Of Problems Does The CVS Test Diagnose?
Chorionic villus sampling can diagnose most of the chromosomal issues and several hundreds of genetic issues. Some of the commonly searched defects by performing chorionic villus sampling are the down syndrome, cystic fibrosis, Tay-Sachs disease, sickle cell anemia, etc.
What Are The Advantages Of Chorionic Villus Sampling?
CVS is done early in pregnancy (first trimester), and the results are obtained within ten days. If the test results are abnormal, it allows the couple to choose between terminating the pregnancy at the beginning of the pregnancy itself. It is much safer to terminate the pregnancy in the early stage.
When Is Chorionic Villus Sampling Performed?
Not everybody pregnant should undergo CVS. CVS is performed when the expecting mother has increased chances of having a child with a birth defect or hereditary issue.
The doctor may suggest CVS if:
- The expecting mother is above 35. Once the women have crossed the age of 35, the chances of having a child with chromosomal abnormality increases
- If father or mother or both the parents have certain genetic disorder
- If the expecting mother has undergone one or more spontaneous abortions in her previous pregnancies without any significant reasons
- If the father or mother or both parents have a family history of genetic issue
- If the parents already have a child with genetic issues like down syndrome
- If other prenatal tests show some abnormal results
How Is Chorionic Villus Sampling Performed?
The objective of the procedure of chorionic villus sampling is to collect the cells from the chorionic villus. This is performed 10 to 13 weeks after the last menstrual period by an experienced perinatologist. During this procedure, a thin tube is inserted through the vagina (transcervical). Alternatively, a long thin needle is put through the abdomen (transabdominal) towards the placenta. The cells are collected into the tube, which is removed slowly and carefully . The whole procedure is assisted by an ultrasound to find the right spot. After the procedure, the doctor will check the heartbeat of the baby and maternal blood pressure, breathing, etc. to make sure there are no complications.
How Are CVS Test Results Evaluated?
As in the case of all prenatal tests, CVS also cannot measure the severity of the abnormality. However, the results are highly reliable, as they possess 98% accuracy. One drawback of CVS is that it is not able to detect the neural tube defect of the baby. Sometimes a false positive result is obtained in which abnormal genetic material other than that of the baby is found in the villus. Further tests like amniocentesis are needed to get clarity and confirm the issue
What Are The Risk Of Chorionic Villus Sampling?
Although CVS is a safe procedure, it does have a potential risk as it is an invasive diagnostic test. Miscarriage is the most significant risk associated with this test. It can happen in one out of every hundred CVS performed. Nevertheless, if a very experienced and skilled perinatologist performs the test, it can decrease to one in every 400 procedures. Other issues that may occur after performing CVS are:
- Abdominal cramping
- Vaginal spotting
- Leakage of amniotic fluid
- Soreness in the belly area(if performed trans abdominal)
Mostly these issues will resolve on their own in a couple of days. Very rarely CVS can cause:
- Uterine infection
- Rh sensitization (Baby’s blood cells entering into mother’s bloodstream). If the Rh group varies with mother and child, Rh-immune globulin shot is given to the mother after the procedure to avoid the production of antibody against the RBC of the fetus which can cross the placenta and destroy the RBC of the baby
Chorionic Villus Sampling Vs. Amniocentesis?
Amniocentesis, another kind of prenatal test, which is conducted to detect the genetic issues of the fetus, can only be performed around the 16th week of pregnancy. By then, the pregnancy will get into the second trimester, whereas CVS can be performed as earlier as 10 to 13th week of gestation. The result is also obtained faster in CVS than an amniocentesis.
When To Seek Medical Attention After The Procedure?
Though minor cramps, spotting, and fluid leakage is common during CVS, but seek immediate medical attention, if the expecting mother experiences:
- Moderate to severe cramps instead of slight one
- Moderate to severe bright red bleeding instead of spotting
- Excessive leakage of amniotic fluid
When is CVS Is Not Recommended?
CVS is not recommended for expecting mothers:
- Who is bearing more than one child
- Who are already experiencing vaginal bleeding or spotting
- Who are already experiencing some sort of infections
Transcervical CVS is not recommended if the mother has a tilted uterus or have fibroids.
Though CVS has its potential risk, the benefits from the results outweigh the risk. So you can go ahead with the decision of your doctor to perform CVS.