Great care is taken to first locate the position of the foetus by ultrasound and then to guide the needle into the amniotic sac where the fluid can be sampled at a safe distance from the foetus.  NOTE:  The bladder must be full to ensure good abdominal ultrasound results, so plenty of water should be consumed prior to the test. 

During the procedure, the woman may feel a sharp localized pain both when the needle enters the skin and again when it passes into the uterus.

Hollow Needle

The risks of damage or infection in the foetus as a consequence of the procedure are significant and need to be discussed in detail between both parents and your medical practitioner. Having said that, this test is often only carried out if a high risk pregnancy has been identified by the 'Triple Test', so in these cases, some doctors believe that the potential results clearly outweigh the risks.

The estimates of the level of risk vary between locations, however it is generally quoted that a risk of 0.25% to 0.5% exists.  This may seem small but when one considers that this means that between 1 in 400 to 1 in 200 procedures result in infection, damage or miscarriage, then the numbers do not look so bright.

This test is normally taken between the beginning of the 15th week (13 weeks from conception) and end of the 17th week (15 weeks from conception). 

There are normally two main reasons for taking this test; either an abnormal triple test result has been returned or alternatively the parents have opted to have a chromosomal analysis performed using this technique (this may be for personal reasons or if a family history of problems exists). 

NOTE: In some countries, this may be the only invasive test available if CVS diagnosis is not generally available except under extreme circumstances due to the higher risks involved.  

NOTE: In Women with Rh-Negative blood that are carrying an Rh-Positive baby, this procedure can also help in deciding if early delivery is required or if a foetal blood transfusion will be needed.  See the article on RH Disease for a detailed explanation.

To perform the Chromosome Analysis, the cells in the extracted fluid are placed in a culture and stimulated to grow for about 10 days.  A cell extraction and staining process is then used to be able to see the chromosomes so that a process of identification, counting and matching into pairs can be done.  This can then be analysed for evidence of extra or missing chromosomes.

After the procedure, the mother should avoid any lifting for a few days and rest as much as possible to avoid any ruptures that may occur as a result of the slightly weakened uterus wall.  Some very light cramps are normal for the first day, but any prolonged or heavy cramping or fever as well as any discharge of fluid or blood from the vagina should be reported immediately to your practitioner.

What is the accuracy?

• 99% of all tested chromosome disorders

Introduction

1. The Triple Test - Overview

2. The Triple Test - Detail and Results

3. Amniocentesis

4. CVS