Chorionic villus sampling (CVS) is a prenatal diagnostic test that involves taking a small tissue sample from the finger-like projections of the placenta, called as the chorionic villi. The sample is then tested for various chromosomal abnormalities.
At present, we can determine conditions like Down’s syndrome, sickle cell anemia and most of the types of cystic fibrosis with CVS, but not anatomical malformations like neural tube defects. This method is mainly used with mothers where children are at a high-risk of developing abnormalities, and is believed that with the advancements in the fields of medical science and chromosomal studies, more than a 1000 conditions will be detected by CVS in the near future.
CVS is usually done between the 10th and 13th weeks of pregnancy. Thus, as it is done early, during the first trimester, and results are obtained faster, it is beneficial. This is because, in case there are some serious abnormalities, the mother can go ahead with medical termination of pregnancy (MTP) at an early stage, which is less traumatic and risk as compared to MTP of a late-stage pregnancy.
It can be done with two methods- A) Transcervical CVS: In which the sample is collected by inserting a tube into the uterus through the vagina, or B) Transabdominal CVS: In which a needle is inserted into the uterus through the abdominal wall. Both the methods are done under ultrasound guidance; and take up to 30 minutes to be completed; however, the actual sample collection takes only about 2 minutes.
In the transcervical method, the woman is lying on her back, whereas, in the transabdominal method, she is lying tummy up. Though the latter is equally safe, transcervical method usually provokes lesser anxiety in the mother, as the needle-fear can be over-whelming. CVS is regarded as a safe procedure. The risk of fetal loss or damage is low (1 in 370).
It is usually done in hospital setup; however certain doctors’ may carry it out in their private clinics as well. The pain during the needle or tube insertion is mild to moderate; and some women may complain of spotting after the procedure or cramping. Though this may not be anything major, if the spotting does not stop after 2 days, report to the doctor immediately.
The cramping also is usually mild, somewhat similar to what occurs during menstrual cycle, and subsides after a day or two. Since we are collecting the part of placenta which connects to the fetus, the results are more accurate and can be regarded as diagnostic over the other screening tests. It has 98% sensitivity and specificity, and after the sample collection, results are obtained in a week’s time.
The risk of infection after the procedure is also regarded as low; and any development of fever after the test also should be reported immediately to the doctor. It’s important to choose a correct centre for the procedure. Also if one avoids the procedure till at least the first 10 weeks of pregnancy are completed, the risks associated with CVS can be reduced.