The earliest test which a woman can choose to have is chorionic villus sampling. For most women, the main attraction of this test is the fact that, should the result be abnormal, the pregnancy can be brought to an end at an early stage.

As with every aspect of the care she receives during pregnancy, in labour and after the birth of her baby, how the woman copes with antenatal testing depends to a very large extent on the support she receives.

Fully understanding what is happening makes the procedure itself much more bearable.

Research shows that chorionic villus sampling is associated with more miscarriages than amniocentesis. Some women who are old enough to be at increased risk of having a Down's baby decide against the chorionic villus sampling test for this reason.

There have been some reports that having chorionic villus sampling very early in pregnancy, before 11 weeks, may result in the baby's being born with abnormal arms and legs. Although chorionic villus sampling is now performed later than it used to be, some couples remain anxious that there may still be a risk of their baby being hurt by the test.

What is clear from the different reasons which motivate women either to have or not to have chorionic villus sampling is that the decision is ultimately a very personal one. There are no absolute rights or wrongs about antenatal testing; the decision to have a test can only be based on what each individual woman sees as its advantages and disadvantages.