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 chromosomal condition such as Down's syndrome, Edwards' syndrome or Patau's syndrome 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 a definitive result in around 99% of cases. However, it cannot test for every birth defect 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 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 conditions 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 test only checks for conditions caused by faulty genes, and it cannot exclude every possible condition.
If your test is "positive", your baby has one 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 the test finds that your baby will be born with a condition, you can speak to a number of specialists about what this means.
These could include your midwife, a consultant paediatrician, a geneticist and/or 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 one of these conditions will always have the condition, so you'll need to consider your options carefully. Your main options are:
This can be a very difficult decision, but you don't have to make it on your own.
As well as discussing it with specialist healthcare professionals, talk things over with your partner and speak to close friends and family, if you think it might help.
The charities Antenatal Results and Choices (ARC), Down's Syndrome Association, Sickle Cell Society and SOFT (Support Organisation for Trisomy 13 and 18) can also offer support and information.