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 your choice whether you have the diagnostic tests or not.

Your healthcare professional will talk it through with you and answer any questions you have. They'll 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 placenta is inside your womb. It links your blood to your baby and provides nourishment.

Chromosomes from the placenta can be counted from the sample. CVS does not give a clear result in around 2 in every 100 samples. If this happens you may be offered a repeat test. Your obstetrician will help you understand what your results mean.

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 1 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 aren't completely safe. There are some risks but they’re the only way to know for sure if your baby has a condition. It’s your choice and healthcare professionals will support you whatever you decide.

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, sometimes painful.

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 afterward.

Urgent advice: Speak to your midwife if:

  • pain or discomfort lasts more than a day or two after a diagnostic test
  • you have any worries following a diagnostic test

Referral to the fetal medicine team

Your healthcare 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 chromosomal conditions you or your baby might have. You’ll usually have an appointment within a few days.

Support for decisions following diagnostic testing

If the diagnostic test shows your baby does have one of the conditions, your midwife or obstetrician will discuss your result with you and give you time to understand what it means.

Some parents may decide to continue with the pregnancy, while others will feel that ending the pregnancy is right for them. Only you can decide what is best for you and your family.

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 help provide information and emotional and practical support. This can include more information about living with the condition your baby has or is likely to have.

If you need to choose what to do next, support organisations and healthcare 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 supports expectant and new parents to make informed decisions by providing up-to-date, accurate and balanced information about people living with Down's syndrome.

Phone: 0300 030 2121


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

Phone: 0300 102 7638

Antenatal Results and Choices (ARC)

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

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

Last updated:
23 January 2023

Other languages and formats

British Sign Language (BSL)  |  Audio