Diagnostic tests in early pregnancy

What is involved in diagnostic test in early pregnancy and what does it involve?

•   Chorionic villus sampling
•   Amniocentesis
•   Testing twins

Chorionic villus sampling (CVS)

This is a diagnostic test which can tell you for certain whether your baby has Down’s syndrome or another genetic abnormality. The test can’t tell you whether your baby has spina bifida.

When is the test carried out?

Between 11 and 13 weeks of pregnancy.

You have to wait about 10 days for the results. This means that if your baby has Down’s and you want to terminate your pregnancy, you can do so well before you start to feel your baby kicking.

A fine needle is put through your abdomen and, using an ultrasound scan for guidance, the doctor removes a very small part of the placenta.

CVS is an early pregnancy test and the results don’t take long to come through. If you decide to terminate your pregnancy, it may be less traumatic than if you have to make the decision later on.

There’s a small risk of miscarriage, estimated to be between 0.5 and 2 per cent.

Your chances of miscarrying after the test will depend very much on where you have it carried out. Large hospitals which do more than 100 CVS tests a year are likely to have very low miscarriage rates. Smaller units where fewer CVS tests are performed may well have higher rates of miscarriage. It’s a question of whether the doctors have had plenty of opportunity to refine their skills. Ask the hospital you attend what its miscarriage rate is following CVS. If you feel it is too high (in some hospitals it is more than 2 per cent) then ask to be referred to a different hospital.

This is also a diagnostic test. It can tell you for certain whether your baby has Down’s syndrome or another genetic abnormality or spina bifida.

As early as 13 weeks of pregnancy but more usually, at about 18 weeks.

Some laboratories with very sophisticated equipment can get the results back to you in 10 days, but most take about three weeks. So you could find yourself having to make a decision about termination when you are more than half way through your pregnancy.

You need to have an empty bladder. Then, using ultrasound for guidance, the doctor will put a long needle through your abdomen and draw off about 20ml of the fluid which surrounds your baby (amniotic fluid). After the test, your baby’s heartbeat will be checked and you’ll be invited to rest for an hour at the hospital. You should then spend another two days very quietly at home to minimise the risk of miscarriage.

Advantages

The test checks your baby for a wide range of genetic abnormalities and for spina bifida as well.

Disadvantages

As with CVS, there’s a 0.5 to 2 per cent risk that you will miscarry after amniocentesis.

Waiting three weeks for the results can be very difficult.