Chorionic villus test in pregnancy – chorionic villus sampling or, abbreviated, CVS is an optional medical investigation that is performed, if the doctor finds it necessary, between the weeks 10 and 14 of pregnancy. This medical test serves to detect certain genetic or chromosomal abnormalities of the feotus and has diagnostic value. The chorionic villus test or chorionic villus sampling will almost certainly tell if the foetus suffers from chromosomal abnormalities such as Down syndrome or other genetic disorders such as sickle cell anaemia, Tay-Sachs disease or cystic fibrosis. The test indicates with diagnostic value whether the foetus has chromosomal and genetic abnormalities and also shows the sex of the foetus. Very rarely this test identifies a chromosomal abnormality that is not really there – in these cases we recommend other tests, such as amniocentesis.
How is the chorionic villus test performed?
The chorionic villus sampling (CVS) involves taking some tissue of the placenta. The doctor uses a small, thin tube with which he reaches the uterus through the vagina, or uses a thin needle that pierces the woman’s belly. The sample of placenta contains genetic information and will be subjected to medical analyses; it can accurately identify foetal abnormalities. If the tissue is obtained by piercing the woman’s belly, local anaesthesia is used. The procedure itself – trans-vaginal or trans-abdominal – is not painful, does not take long time, but the woman may feel some discomfort. In no more than 15-17 days, you will have a result.
After testing, it’s recommended to stay in bed, to rest all day and to make little effort for another 2-3 days; in case you have stomach cramps, you can take a dose of acetaminophen. You may have mild vaginal bleeding after the investigation – there is nothing out of the ordinary, but you should inform your doctor. If, however, vaginal bleeding is profuse, if you notice an abundant colourless vaginal discharge, uterine contractions or if you experience great abdominal pain, if you have fever or chills, call your doctor immediately.
Chorionic villus test is by no means a routine medical test during pregnancy. It is a special test recommended only in certain situations. It is important to know the risks of this test: the procedure may be followed by miscarriage – the risk is not too high, about 1 – 2%, but it exists and is higher than in the case of an amniocentesis. In addition, this test involves the risk of transmission of HIV infection from mother to foetus. Because of the risks involved after this test, your doctor may recommend a series of further tests to check the baby, to see if the baby was affected – usually an ultrasound. Because of the high risks involved, you should decide to make the chorionic villus test only together with your doctor and only after you balance the utility of the test and its risks. Amniocentesis is a medical investigation that has the same role and the same accuracy but, unfortunately, is not performed earlier than the 15th week of pregnancy; so if the existing risk of foetal abnormalities is increased, you cannot delay the investigation and therefore you will have the chorionic villus test. However, amniocentesis also presents the risk of spontaneous abortion, only that the risk is slightly lower – 0.5%. CVS is preferred because if a severe foetal anomaly is detected, it’s still early and the termination of pregnancy is possible. However, in case of a positive result, you should talk to a specialist and assess the situation.
When to perform the chorionic villus testing – chorionic villus sampling?
- When the future mother is over the age of 35-40 years old;
• When the result of first trimester screening is positive (this screening refers to a blood test and an ultrasound (nuchal translucency) that has no diagnostic value, but can show the existence of foetal anomalies – when getting positive results, subsequent testing is needed) ;
• When the future mother or the future father have in their personal history or in their family history cases of genetic disorders;
• When the woman had a previous pregnancy with such problems;