Chorionic villus sample. Doctor's hand holds a tube containing a red chorionic villus sample drawn from a pregnant woman. In the background are ultrasound screens used to visualise the womb of the pregnant woman. Ultrasound imaging enables a syringe needle to be directed into the woman's abdomen to chorionic villi tissue of the foetus which is found in the mother's placenta. Chorionic villi contain foetal blood vessels and is a way of obtaining foetal blood. Chorionic villus sampling (CVS) is usually conducted between 9-12 weeks of pregnancy to evaluate the chromosomal and DNA status of the foetus. CVS is a way of diagnosing abnormalities in a foetus in early pregnancy.