Indications of performing Chorionic villus sampling, or Amniocentesis

• have had a high risk screening test for Down syndrome
• have had a previous pregnancy affected with a genetic disorder
• or your partner have one or more relatives affected with a genetic disorder, which means you are at greater risk of having a child with a genetic disorder, such as cystic fibrosis, thalassaemia or sickle cell disease
• have received a result from a scan which shows certain abnormal ultrasound features, such as fluid collection at the back of the baby's neck (nuchal translucency), or a congenital heart defect which indicates the baby may have a disorder such as Down syndrome. This may be suspected on a scan at 18-22 weeks
• want to know for certain whether your baby has a genetic disorder or not.

Chorionic Villus Sampling & Amniocentesis in Pregnancy

Chorionic Villus Sampling and amniocentesis are tests carried out during pregnancy, to check your baby for disorders such as Down syndrome and, where appropriate, rarer specific inherited disorders. Amniocentesis is also occasionally done to test for other disorders in pregnancy such as fetal infection.

In CVS a small sample of the placenta (afterbirth) is taken for testing, whereas in amniocentesis a small amount of amniotic fluid - the water around your baby inside your uterus (womb) - is taken for testing.

CVS is performed most commonly between 11 and 13 weeks. Amniocentesis is performed after 15 weeks.