If a screening test shows that there is a risk of problems, a diagnostic test can be carried out to give more exact information about the baby. These are quite common procedures, which are carried out for a number of reasons. In many cases they are used to look at the structure and number of chromosomes and so establish any genetic problems in the baby. Both CVS and amniocentesis are carried out under the guidance of ultrasound.
With any diagnostic test, it is important to understand the reasons for having it and the possible consequences. In some cases such tests may provide information about a pregnancy that was not expected. For example, a diagnostic test may be carried out to check for Down's syndrome but may reveal that the baby has a different chromosomal abnormality such as Klinefelter's syndrome or Turner syndrome.
Both CVS and amniocentesis carry a risk of damage to the baby and miscarriage. This risk is between 1% and 2%. For example, for every 100 women who chose to have a diagnostic test, one or two of them will miscarry as a result.
Although diagnostic tests are 99% accurate, they could very occasionally give incorrect results.
