Chorionic villus sampling - Why it's offered 

Why chorionic villus sampling is offered 

Chorionic villus sampling (CVS) is offered to pregnant women at risk of having a baby with a serious genetic disorder. It will diagnose any problems at an early stage.

CVS isn't routinely offered to all women during pregnancy. It's offered if your test results or medical or family history suggest you have an increased chance of having a baby with a genetic disorder.

You don't have to have the test if it's offered – it's up to you to decide whether you want it.

What conditions can CVS detect?

CVS can be used to diagnose a number of serious genetic disorders, including:

• Down's syndrome – a condition that typically causes some level of learning disability and a characteristic range of physical features
• Edward's syndrome and Patau's syndrome – conditions that can result in miscarriage, stillbirth or (in babies that survive) severe physical problems and learning disabilities
• cystic fibrosis – a condition in which the lungs and digestive system become clogged with thick, sticky mucus
• Duchenne muscular dystrophy – a condition that causes progressive muscle weakness and disability
• thalassaemia – a condition that affects the red blood cells, which can cause anaemia, restricted growth and organ damage
• sickle-cell anaemia – where the red blood cells develop abnormally and are unable to carry oxygen around the body properly
• phenylketonuria – where your body cannot break down a substance called phenylalanine, which can build up to dangerous levels in the brain

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

Deciding whether to have CVS

If you're offered CVS, ask your doctor or midwife what the procedure involves and what the risks and benefits are before deciding whether to have it.

You may also find it helpful to contact a support group, such as Antenatal Results and Choices (ARC). ARC is a charity that offers information, advice and support on all issues related to screening during pregnancy.

Reasons to have CVS

The test will usually tell you whether your baby will be born with any of the genetic conditions that were tested for.

If no problem is found, it may be reassuring. A result showing that a genetic condition was detected will give you plenty of time to decide how you want to proceed with your pregnancy. Read about the results of CVS for more information.

Reasons not to have CVS

There is a 1-2% chance you could have a miscarriage after the procedure. You may feel this risk outweighs the potential benefits of the test. Read more about the risks of CVS.

Some women decide they don't want to know if there's a problem with their baby until later on. You may choose to have an alternative test called amniocentesis later in your pregnancy instead, or you might just want to find out when your baby is born.