Chorionic villus sampling (CVS) allows specific genetic disorders to be diagnosed in the foetus at a very early stage.

If a condition is identified that cannot be treated, or if it causes severe disability in the child, the child’s parents may decide to have an abortion. If the parents choose to continue with the pregnancy, CVS provides early notice of the condition, giving them plenty of time to prepare for the challenges ahead.

Some of the foetal disorders that can be detected by CVS include:

• chromosomal conditions such as Down's syndrome, a disorder that affects a person’s physical appearance and their ability to develop mentally
• genetic disorders such as cystic fibrosis, which makes bodily secretions thick and sticky, hindering the function of certain organs
• disorders of the musculoskeletal system such as Duchenne muscular dystrophy, a genetic disorder that causes progressive muscle weakness and disability
• blood disorders such as thalassaemia, a condition that affects your body’s ability to create red blood cells, or sickle-cell anaemia, which affects how your red blood cells carry oxygen around your body 
• metabolic disorders such as antitrypsin deficiency, where your body cannot produce the protein alpha-1 antitrypsin, or phenylketonuria, where your body cannot produce the enzyme phenylalanine hydroxylase
• mental health conditions such as fragile X syndrome, which is a condition that can affect your appearance, intelligence and behaviour

As well as the above conditions, some other, less common conditions may also be diagnosed using CVS.

CVS cannot detect neural tube defects. These are birth defects that affect the brain and the spinal cord, such as spina bifida. These can usually be detected with an ultrasound scan.

If there is a possibility that your unborn baby may have a condition that CVS could detect, your GP or midwife will discuss this with you. You will be given advice about the risks of the procedure and information to help you cope with the results.

In some cases, you may be referred to a genetic counsellor, a healthcare professional who is trained in genetics, for further discussion.