Invasive (Amniocentesis / CVS) Prenatal Testing

These tests may be necessary in pregnant women who:

  • Have received a high-risk screening result from a screening test ( FTS / Quadruple /Triple Test) for Down syndrome or similar problems.
  • Advanced Maternal Age
  • Have had a family or previous pregnancy history of a genetic disorder like Thalassemia
  • Where a Fetal Structural Abnormality is found

The Test

Amniocentesis is a procedure in which a small amount of the amniotic fluid surrounding the baby in the womb is removed by passing a fine needle through the mother’s abdomen. Amniocentesis is performed after 15 weeks of pregnancy.

CVS is a procedure in which a small amount of fetal tissues from the placenta in the womb is removed by passing a fine needle through the mother’s abdomen. CVS is performed at 11-13 weeks of pregnancy.

The Risks

Most women say that having amniocentesis / CVS is uncomfortable rather than painful, a bit like a period pain. Women describe a sharp stinging feeling when the needle goes in and a feeling of pressure when the needle comes out.

You may notice some cramping for a few hours afterwards. This is normal.

If you experience any unusual symptoms after the test, such as feeling shivery (as if you have flu), fluid loss, bleeding or contractions you should seek advice immediately.

Every pregnancy carries a risk of miscarriage. Amniocentesis / CVS involves putting a needle through the wall of the womb. It may sometimes cause a miscarriage due to injury or infection in the womb. The additional overall risk of miscarriage is approximately 1%.

The Interpretation

For most women the laboratory test will give a definite ‘yes’ or ‘no’ answer. The result will let you know, one way or the other, whether the baby has the disorder the test was looking for.

  • Many women who have amniocentesis /CVS will have a ‘normal’ result. In other words, their baby will be born without the disorder(s) the test was looking for.
  • Some women will be informed that the baby has the disorder that the test was looking for. If the results are abnormal, these will be discussed fully with you. For the majority of disorders, there is no treatment or cure. You will need to consider what is best for you and the baby. This might be to:
    1. Terminate this pregnancy – If you decide to end the pregnancy, you will be given full information about what this involves. It will depend upon how many weeks pregnant you are when you make the decision.
    2. Or continue with the pregnancy and use the information you have gained to help prepare for the birth and aftercare of your baby.

The Procedure

Both Amniocentesis and CVS are outpatient procedures and will not need admission. In Amniocentesis, using an ultrasound probe for accurate guidance and to ensure a safe distance from the baby, a fine needle is pushed into skin, through abdomen and womb, under a local anaesthetic.

A small sample (15-20 mls) of the fluid surrounding the baby is removed using a syringe. This fluid is amber/yellow colour but may sometimes be stained with blood. The needle is then taken out and the baby’s heartbeat is checked on ultrasound. The amniotic fluid, which contains some of the baby’s cells, is sent to the laboratory for testing.

In CVS, a small amount of placental sample (Chorionic Villi) is removed using a syringe more or less in the same way.

For a very small group women having Amniocentesis/CVS, not enough fluid/ chorionic tissues can be taken and the needle may need to be re-inserted.

If your blood group is Rh negative, you will be advised to have an injection of anti-D immunoglobulin after the procedure to prevent you from developing antibodies against the baby’s blood cells.

After the procedure you should rest in the clinic for at least half an hour before going home . You should take it easy the rest of the day. You could resume your normal life from the very next day.