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 toyou to decide whether you want it.

What conditions can CVS detect?

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

• Trisomy 21 aconditionthat typically causes some level of learning disability and a characteristic range of physical features
• Edward's syndrome and Patau's syndrome conditionsthat can result in miscarriage , stillbirth or(in babies that survive) severe physicalproblems and learningdisabilities
• cystic fibrosis a conditionin which the lungs and digestive system become clogged with thick, sticky mucus
• Duchenne muscular dystrophy acondition 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 detectedwith an ultrasound scan .

Deciding whether to have CVS

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

You mayalso 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 beborn 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 a1-2% chance you could have a miscarriage after the procedure. You may feel this risk outweighs the potential benefits of the test. You maychoose to have an alternative test called amniocentesis later in yourpregnancy instead, oryou might just want to find out when your baby is born.