Is chorionic villus sampling dangerous?

Gynaecologists sometimes suggest to pregnant women a procedure called chorionic villus sampling. The name itself sparks discomfort, fear, and concerns in many women. "Is my baby ok?" In many cases, lack of knowledge about such tests worsens the anxiety they feel. This is why we have gathered all the information for you in one place: what is the chorionic villus sampling, is it dangerous for a pregnant woman or her fetus, and when do doctors recommend it?

The placenta is the organ surrounding the developing fetus, providing oxygen and nutrients, and removing waste products. The chorionic villi are wispy projections of placental tissue with the same genetic makeup as the fetus. To analyse that genetic material, doctors take a sample of chorionic villus tissue.

The chorionic villus sampling is performed between weeks 11 and 13 of pregnancy, most often in week 12. Gynaecologists recommend it to women with an increased risk of their child having chromosomal abnormalities and/or monogenic diseases. This risk is usually higher in older pregnant women (after 37) as well as when other first-trimester screening tests (nuchal scan, double or quad marker scan) show an increased risk of a particular genetic abnormality. Chorionic villus sampling is also advised to couples with abnormal results of a non-invasive prenatal test (NIPT by GenePlanet), which detects the most common chromosomal abnormalities with 99% accuracy.

How is chorionic villus sampling performed?

The process involves taking a small sample of tissue from the developing placenta. With the help of an ultrasound, the doctor determines the position of the fetus and placenta and then penetrates the abdominal and uterine wall with a thin needle. He then removes a sample of the chorion villus tissue. This tissue is then sent to the lab, where they analyse the child’s DNA and determine if any of the tested genetic abnormalities are present.

Very reliable results on the one hand and the risk on the other

The primary purpose of the chorionic villus sampling is to detect Down syndrome and other chromosomal and genetic abnormalities. It detects three most common changes in the number of chromosomes (trisomy 21, 18, and 13), i.e. Down, Edwards, and Patau syndrome, as well as changes in chromosome structure (duplication, deletion, and translocation). The positive side of the chorionic villus sampling is its very high – more than 99% – diagnostic accuracy. But because of its invasiveness, it also has drawbacks: the test can lead to complications such as unwanted miscarriage, which happens in 1–2% of cases.

However, if a woman receives a high-risk result from a screening test, it should be confirmed with a diagnostic method, such as chorionic villus sampling or amniocentesis.