Couples at risk of having children with a serious genetic condition may seek genetic counselling before starting a family. Some may then decide to have a prenatal - 'before birth' - test. To obtain a sample from a fetus, doctors can carry out either chorionic villus sampling (CVS) at 10-12 weeks of pregnancy or amniocentesis at 14-15 weeks. Both techniques provide enough DNA for genetic testing. If the test results indicate that there is a high risk of the fetus being affected, the couple may decide to terminate the pregnancy.