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Chorionic Villus sampling

Chorionic villus sampling (CVS) is a test available to all pregnant women. It is particularly helpful to those with a family history of inherited disorders or who are over the age of 35. It is an alternative to amniocentesis, to test for serious foetal problems, and CVS has the advantage that it can be done earlier than amniocentesis, at about ten weeks after fertilisation. It takes around 20 minutes to perform.

At an early stage the embryo forms itself into two parts, one becoming the developing baby and the other developing into the placenta (afterbirth). The part that forms the placenta starts out as finger-like sections called chorionic villi, which burrow into the wall of the womb to come close to the mother’s blood vessels. These villi are formed by the division of the original fertilised egg and so they have exactly the same DNA (genetic codes) as the embryo does, including any possible genetic abnormality. Any defect in one will be present in the other.

CVS is not entirely without risk. In around 2% of cases the procedure results in miscarriage (spontaneous abortion). However, this can be weighed against the high natural risk of miscarriage during the first trimester: as many as 1 in 4 pregnancies.

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