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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 involves removing a small sample of cells from the placenta. 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 ways of doing this, depending on the position of the placenta:

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

Both types of CVS will be done during an ultrasound scan, which will help to guide the needle or tube into the right place.

Risks of CVS

1 in 200 women who have a CVS will have a miscarriage. Symptoms of miscarriage usually happen 2 to 3 days after the CVS. Other risks can include infection or needing to have a second test if the first does not give a clear result.


Amniocentesis involves inserting a needle into your tummy during an ultrasound scan and taking a small sample of the fluid (“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 16 weeks of pregnancy and is highly accurate.

The needle doesn't touch your baby. Your baby’s heart beat will be checked before and after the amniocentesis.

Risks of amniocentesis

1 in 200 women who have an amniocentesis will have a miscarriage. However, in recent years research has suggested that the risk of miscarriage in this case may have gone down to 1 in 1,000.

Other risks include:

  • Infection.
  • 1 in 20 women may get bleeding from their vagina, tummy cramping or leaking of amniotic fluid from their vagina.
  • The test not giving a clear result - if this happens it would need to be repeated.


It usually takes 2 to 3 weeks to get the results. However, some maternity hospitals can get results after a few days.

Talk to your obstetrician or midwife about whether you want to get your results in person or by phone.

When to get medical help

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

You should contact your maternity hospital immediately if you have:

page last reviewed: 17/05/2019
next review due: 17/05/2022