Introduction

Chorionic villus sampling (CVS) is a test you may be offered during pregnancy to check if your baby hasagenetic or chromosomal condition, such as Downs, Edwards' or Patau's syndromes.

It involves removing and testing a small sample of cells from the placenta (the organ linking the mothers blood supply with her unborn babys).

When CVS is offered

CVS isn't routinely offered to all pregnant women. It's only offered if there's a high risk your baby could have a genetic or chromosomal condition.

This could be because:

• an earlier antenatal screening test has suggested there may be a problem, such as Trisomy 21 , Edward's syndrome or Patau's syndrome
• you've had a previous pregnancy with these problems
• you have a family history of a genetic condition, such as sickle cell disease , thalassaemia , cystic fibrosis or muscular dystrophy , andan abnormality is detected in your baby during a routine ultrasound scan

It's important to remember that you don't have to have CVS if it's offered. It's up to you to decide whether you want it.

Your midwife or doctor will speak to you about what the test involves, and let you know what the possible benefits and risks are, to help you make a decision.

The CVS procedure is usually described as being uncomfortable rather than painful, although you may experience some cramps that are similar to period pains for a day or two afterwards.

There's no cure for most of the conditions CVS finds, so you'll need to consider your options carefully.

You may choose to continue with your pregnancy, while gathering information about the condition so you're fully prepared, or you may consider having a termination ( abortion ).

This is estimated to occur in 0.5% to 1% of women who have CVS.

There are also some other risks, such as infection or needing to have the procedure again because it wasn't possible to accurately testthe first sample that was removed.

The risk of CVS causingcomplications is higher if it's carried out before the 10th week of pregnancy, which is why the test is only carried out after this point.

This is where a small sample of amniotic fluid (the fluid that surrounds the baby in the womb) is removed for testing.

It's usually carried out between the 15th and 18th week of pregnancy, although it can be performed later than this if necessary.

This test has a similar risk of causing a miscarriage, but your pregnancywill beat a more advanced stage before you can get the results, so you'll have a bit less time toconsider your options.

If you're offered tests to look for a genetic or chromosomal condition in your baby, a specialist involved in carrying out the test will be able to discuss the different options with you, and help you make a decision.