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Diagnostic tests during pregnancy

Diagnostic tests are sometimes done during pregnancy to check for chromosomal and genetic conditions in unborn babies.

These can include:

  • Down syndrome
  • Edwards’ syndrome
  • Patau’s syndrome

Your obstetrician or midwife will offer you a diagnostic test if:

  • your screening test or ultrasound scan suggests that your baby may be at risk of having 1 of these conditions
  • you have had a baby with a serious medical or genetic condition before

Making an informed choice

Diagnostic tests are usually the only way to be sure if your baby has certain health problems.

Depending on the result, they can:

  • reassure you that your baby is not at risk of having a specific condition
  • help you decide if you want to continue with your pregnancy
  • give you time to prepare for a baby with special needs
  • help you plan care for your baby after they are born

But diagnostic tests can:

  • be invasive
  • never be 100% accurate
  • increase the risk of miscarriage
  • increase your anxiety - especially if you feel you would continue with your pregnancy regardless of the results

Ask your obstetrician or midwife to explain the risks involved in diagnostic tests.

Types of diagnostic tests in pregnancy

The most common diagnostic tests done during pregnancy are:

  • chorionic villus sampling (CVS)
  • amniocentesis

These tests are uncomfortable. It's normal to get cramps like period pain for a few days afterwards.

Chorionic villus sampling (CVS)

A CVS is when a small sample of cells from the placenta (afterbirth) is removed. These cells can be used to test your baby for chromosomal and genetic conditions.

This is usually done between 11 and 12 weeks of pregnancy, but can sometimes be done up to 14 weeks.

There are 2 types of CVS:

  • a transabdominal CVS - inserting a needle into your tummy
  • a transcervical CVS - inserting a thin tube into your cervix (the neck of your womb)

The type of CVS you have will depend on the position of your placenta. Both types of CVS will be done during an ultrasound scan. This helps the healthcare professional guide the needle or tube into the right place.

Risks of CVS

1 or 2 in every 200 women who have a CVS will have a miscarriage. Symptoms of miscarriage usually start 2 to 3 days after the CVS.

1 to 2 in every 100 women who have a CVS, will have results that may not be a true reflection of their baby’s condition. This is called a false positive. It is when your results wrongly say that your baby has the condition that it was tested for. A false positive happens because of abnormalities in the cells of your placenta, not your baby. This is known as placental mosaicism.

Other risks can include infection or the need for a second test if the first does not give a clear result.


Amniocentesis involves inserting a needle into your tummy during an ultrasound scan. A small sample is taken of the amniotic fluid that surrounds your baby. This can be used to test your baby for chromosomal and genetic conditions.

The test is usually done after 15 weeks of pregnancy and is very accurate.

The needle does not touch your baby. Your baby’s heartbeat will be checked before and after the amniocentesis.

It can take up to 2 to 3 weeks to get the full results.

Your obstetrician or specialist midwife will talk to you about how you will get the results.

Risks of amniocentesis

1 in 300 women who have an amniocentesis will have a miscarriage.

Other risks include:

  • infection
  • bleeding or leaking of amniotic fluid from the vagina
  • tummy cramping
  • no clear result - if this happens it will need to be repeated

When to get medical help

Both tests are uncomfortable. It's normal to get cramps similar to period pains for a few days afterwards.

Non-urgent advice: You should contact the maternity hospital immediately if you have:

  • any fluid leaking from your vagina
  • severe tummy pain
  • any bleeding from your vagina
  • a general feeling of being unwell
  • a fever or temperature over 38 degrees Celsius

Abnormal results from a diagnostic test in pregnancy

Being told that there is something wrong with your baby is extremely difficult. If your test shows that your baby has a genetic or chromosomal abnormality, your healthcare team will discuss your options with you.

Sometimes it can be difficult to find out if your baby has a certain condition. This can mean it will take some time to give you a full diagnosis.

It's important you understand everything your doctor is telling you. If there is anything you don't understand, stop them and ask them to explain.

You can also ask your doctor:

  • as many questions as you need to
  • for an interpreter if English is not your first language
  • about the support available to you, including where you can get helpful and reliable information

You will usually have time to decide what you are going to do. Your midwife and obstetrician will support your decision.

Continuing your pregnancy

If you choose to continue your pregnancy, talk to your healthcare team and discuss what care your baby will need.

Ending your pregnancy

You may decide to end your pregnancy.

If you choose to end your pregnancy, your healthcare team will discuss your options with you, including:

  • the most suitable type of termination - medical (with tablets) or surgical (much less common)
  • where to have the procedure

There is no right or wrong way to feel in this situation. It is normal to grieve for your baby.

There is counselling and support available for free.

Deciding to have an abortion

More support

There are organisations that can offer you and your family more support.

Pregnancy and Infant Loss Ireland -

SOFT Ireland -

Down Syndrome Ireland -

Page last reviewed: 22 December 2023
Next review due: 22 December 2026