Results of chorionic villus sampling

After chorionic villus sampling (CVS) has been carried out, the sample of cells will be sent to a laboratory to be tested.

The number of chromosomes (bundles of genes)in the cells can be counted, and the structure of the chromosomes can be checked for any abnormalities.

If CVS is being carried out to test for a specific genetic disorder, the cells in the sample can also be tested for this.

Getting the results

The first results should be available within three working days, and this will tell you whether a major chromosome problem such as Trisomy 21 has been found.

If rarer conditions are also being tested for, it can take two to three weeks or more for the results to come back.

You can usually choose whether to get the results over the phone or during a face-to-face meeting at the hospital or at home. You'll also receive written confirmation of the results.

How reliable are the results?

CVS is estimated to give adefinitive result inaround99% of cases. However, it cannot test for every birth defect and it's not always possible to get a conclusive result.

Ina very small number ofcases, the results of CVS cannot establish with certainty that the chromosomes in the baby are normal or not. This might be because the sample of cells removed was too small or there's a possibility the abnormality is just in the placenta and not the baby.

If this happens, it may be necessary to have amniocentesis (an alternative test, in which a sample of amniotic fluid is taken from the mother) a few weeks later to confirm a diagnosis.

What the results mean

For many women who have CVS, the results of the procedure will be "normal". This means that none of the genetic disorders that were tested for were found in the baby.

However, a normal result doesn't guarantee that your baby will be completely healthy, as the testonly checks for conditions caused by faulty genes, and it cannot exclude every possible genetic disorder.

If your test is "positive", your baby has one of the disorders it was tested for. In this instance, the implications will be fully discussed with you and you'll need to decide how to proceed.

What happens if a problem is found

If the test finds thatyour baby will be born with a genetic disorder, you'll speak to a number of specialists about what this means.

This may be your midwife, adoctor withexperience in childhood genetic conditions, a geneticist and/or a genetic counsellor.

They'll be able to give you detailed information about the condition including the problems your child may have,the treatment and support they might need,and whethertheir life expectancy will be affected to help you decide what to do.

There's no cure for most genetic conditions, so you'll need to consider your options carefully. Your main options are:

  • continue with your pregnancy while gathering information about the condition, so you're prepared for caring for your baby
  • have a termination( abortion ) read more about termination for foetal abnormalities

This can be a very difficult decision, but you don't have to make iton your own.

As well asdiscussing it withspecialist healthcare professionals, talk things over with your partner andspeak to close friends and family, if you think it might help.The charity Antenatal Results and Choices (ARC) can also offer support and impartial information.

Content supplied by the NHS Website

Medically Reviewed by a doctor on 28 Nov 2016