Diagnostic tests in pregnancy

Diagnostic tests are offered to women whose screening tests show:

  • they have a higher chance of being a carrier for (or having) sickle cell or thalassaemia
  • a higher chance their baby may have either Down’s syndrome, Edwards’ syndrome or Patau’s syndrome

These tests can tell you for sure if your baby has any of these.

It’s very important you know that it’s your choice whether you have the diagnostic tests or not.

Your health professional will talk it through with you and answer any questions you have. They will support you to make decisions that feel right for you.

The tests

There are 2 types of diagnostic tests: chorionic villus sampling (CVS) and amniocentesis.

Chorionic villus sampling (CVS)

CVS can be done from 11 weeks of pregnancy. It’s usually only offered in a specialist centre.

With the help of an ultrasound scan, a specialist doctor (obstetrician) will guide a fine needle through your abdomen (tummy) and will take a small sample of tissue from the placenta (the organ linking your blood supply with your unborn baby’s).

Chromosomes from the placenta can be counted from the sample. CVS does not give a clear result in around two in every 100 samples. If this happens you may be offered a repeat test.

More about CVS


Amniocentesis (you might hear it shortened to ‘amnio’) can be carried out after 15 weeks of pregnancy. It usually takes about 10 minutes.

An ultrasound scan will check your baby’s position in the womb. The specialist doctor (obstetrician) will guide a fine needle through your abdomen (tummy) into your womb. The doctor can then take a sample of the fluid surrounding your baby (called amniotic fluid).

Your baby’s chromosomes can be counted from the sample. Amniocentesis does not give a clear result in around one in every 100 samples. If this happens, you may be offered a repeat test.

More about amniocentesis

How safe are diagnostic tests?

CVS and amniocentesis are not completely safe but they’re the only way to know for sure if your baby has a health condition or chromosomal condition. It’s your choice and health professionals will support you whatever you decide.

Diagnostic tests have some risks. Around 1 in every 200 (0.5%) women who have a diagnostic test will miscarry as a result of the test. The risk may be higher in twin pregnancies.

Are diagnostic tests painful?

Many women find the tests uncomfortable.

Some discomfort in your lower abdomen for a couple of days is usual, and you can take paracetamol for this.

You should take things easy and avoid hard exercise for a day or two afterwards.

If the discomfort carries on beyond this, or if you have any other worries, please contact your midwife.

Referral to the fetal medicine team

Your health professional may refer you to the fetal medicine team.

The team includes a specialist doctor, midwife and other health professionals.

The team, which could be based in another hospital, may offer you further tests and will give information and advice about any health conditions or chromosome conditions you or your baby might have. You’ll usually have an appointment within a few days.

Support for decisions

Results from diagnostic testing may affect whether you decide to continue or end your pregnancy, or you may wish this information to help you prepare for a baby who may need additional care and support.

Tell your midwife if at any point you’re not sure about the choices you’ve made or if you’d like more information

Your midwife will tell you which support organisations can give you more information about living with the condition your baby has, or is very likely to have.

If you need to choose what to do next, support organisations and health professionals can answer any questions you have and support you in reaching decisions that feel best for you and your baby.

Whether you choose to continue with your pregnancy or not, your choices will be respected and you’ll get the care and support you need.

Further information and support

If you need support following a diagnostic test or after receiving your test results contact:

Down’s Syndrome Scotland

Down’s Syndrome Scotland is the only charity in Scotland dedicated to supporting people with Down’s syndrome and their parents, carers and families.

Phone: 0300 030 2121


SOFT UK supports families affected by Patau’s syndrome, Edwards’ syndrome or related disorders.

Antenatal Results and Choices (ARC)

ARC offers non-directive individualised information and support to parents who are making decisions around antenatal testing and whether to continue pregnancy or end pregnancy.

Phone: 0845 077 2290 or 0207 713 7486 from a mobile.