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.
If CVS is being carried out to test for a specific genetic condition, the cells in the sample can also be tested for this.
Getting the results
The first results should be available within 3 working days.
If rarer conditions are also being tested for, it can take 2 to 3 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 a definitive result in 99 out of every 100 women having the test.
But it cannot test for every condition and it's not always possible to get a conclusive result.
In a very small number of cases, the results of CVS cannot establish with certainty if your baby will have the condition the test is looking for.
This might be because the sample of cells removed was too small.
Or there's a possibility there's a change in the structure of the chromosomes in the placenta and not in the baby.
If this happens, it may be necessary to have amniocentesis, an alternative test where a sample of amniotic fluid is taken from the womb.
This is done a few weeks later to confirm a diagnosis.
What the results mean
Many women who have CVS will have a "normal" result. This means that none of the conditions that were tested for were found in the baby.
But as the test only checks for conditions caused by certain genes, it cannot exclude any conditions not tested for.
If your test result is "positive", your baby has 1 of the conditions they were 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 condition is found
If your test results show that your baby will be born with a condition, you can speak to a number of specialists about what this means.
These could include a midwife, a doctor who specialises in children's health (consultant paediatrician), a geneticist and a genetic counsellor.
They'll be able to give you detailed information about the condition, including the possible symptoms your child may have, the treatment and support they might need, and whether their life expectancy will be affected, to help you decide what to do.
A baby born with 1 of these conditions will always have the condition, so you'll need to consider your options carefully.
Your options are to:
- continue with your pregnancy – it can help to find out as much as you can about the condition your baby may have
- end your pregnancy (have a termination)
This can be a very difficult decision, but you do not have to make it on your own.
As well as discussing it with specialist healthcare professionals, it can help to talk things over with your partner and speak to close friends and family.
You can also get support and more information from charities like: